Teses / dissertações: "Yeast strains"

1

Reynolds, Nicola C. "Genetic manipulation of yeast strains". Thesis, University of Greenwich, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276133.

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Govender, Patrick. "Industrial yeast strains engineered for controlled flocculation". Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1450.

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Thesis (PhD (Viticulture and Oenology. Wine Biotechnology))--University of Stellenbosch, 2009.
In many industrial fermentation processes, Saccharomyces cerevisiae yeast should ideally meet two partially conflicting demands. During fermentation a high suspended yeast count is of paramount importance to maintain a rapid fermentation rate, whilst efficient flocculation should ideally be initiated only on completion of the primary alcoholic fermentation, so as to enhance product clarification and recovery. Most commercial wine yeast strains are non-flocculent, probably because this trait was counter-selected to avoid fermentation problems. In this study, we assessed molecular strategies to optimise the flocculation behaviour of non-flocculent laboratory and wine yeast strains. For this purpose, the chromosomal copies of three dominant flocculation genes, FLO1, FLO5 and FLO11, of a non-flocculent S. cerevisiae laboratory strain (FY23) and two commercial wine yeast strains (BM45 and VIN13) were placed under the transcriptional control of the stationary phase-inducible promoters of the S. cerevisiae ADH2 or HSP30 genes. Under standard laboratory media and culture conditions, all six promoter-gene combinations resulted in specific flocculation behaviours in terms of timing and intensity. The data show that the strategy resulted in the expected and stable expression patterns of these genes in both laboratory and industrial wine yeast strains. Most importantly, the data confirm that inducible expression of the native FLO1 and FLO5 open reading frames, albeit to varying degrees, are responsible for a quantifiable cell-cell adhesion phenotype that can be characterized as a Flo1 flocculation phenotype. On the other hand, we found that inducible expression of the native FLO11 ORF under these conditions resulted in flor/biofilm formation and invasive growth phenotypes. However, the specific impact of the expression of individual dominant FLO genes with regard to characteristics such as flocculation efficiency, cell wall hydrophobicity, biofilm formation and substrate adhesion properties showed significant differences between the commercial strains as well as between commercial and laboratory strains. These adhesion phenotype differences may at least in part be attributed to wine yeast FLO gene open reading frames containing significantly smaller intragenic repeat regions than laboratory strains. The data show that the ADH2 regulatory sequences employed in this study were unsuitable for the purpose of driving FLO gene expression under wine-making conditions. However, HSP30p-based FLO1 and FLO5 wine yeast transformants displayed similar flocculent phenotypes under both synthetic and authentic red wine-making conditions, and the intensities of these phenotypes were closely aligned to those observed under nutrient-rich YEPD conditions. The fermentation activities of HSP30p-based transgenic yeast strains were indistinguishable from that of their parental host wine yeast strains. The chemical composition of wines obtained using transgenic yeast strains were similar to those produced by parental strains. The BM45-derived HSP30p-FLO5 transformant in particular was capable of generating compacted or ‘caked’ lees fractions, thereby providing a distinct separation of the fermented wine product and lees fractions. Furthermore, in this study we report a novel FLO11 induced flocculation phenotype that seems to exclusively develop under authentic red wine-making conditions. This strong FLO11 flocculation phenotype was not wine yeast strain dependant, possessed both Ca2+-dependant and Ca2+-independent flocculation characteristics and was insensitive to inhibition by both glucose and mannose. A distinct advantage of this unique FLO11 phenotype was highlighted in its ability to dramatically promote faster lees settling rates. Moreover, wines produced by HSP30p-FLO11 wine yeast transformants were significantly less turbid than those produced by their wild type parental strains. The benefit of this attractive property is it facilitates simpler and faster recovery of wines and also promotes greater volume recovery of the wine product.

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Nayyar, Ashima. "Yeast flocculation : understanding cell surface structure-function relationships in industrial yeast strains". Thesis, Abertay University, 2015. https://rke.abertay.ac.uk/en/studentTheses/cec13693-e667-4426-ba6c-6873e5c2b642.

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Adhesion properties of microorganisms are crucial for many essential biological processes such as sexual reproduction, tissue or substrate invasion, biofilm formation and cell-cell aggregation. One of such controlled forms of cellular adhesion in yeast that occurs preferentially in the liquid environments is a process of asexual aggregation of cells which is also referred to as flocculation. The timing during growth and the causes of onset of yeast flocculation are of commercial interest to the brewing industry, as flocculation can determine the degree of attenuation of the wort. Early or premature flocculation is one common causes of ‘hung’ or ‘stuck’ fermentations giving rise to sweeter beer whereas a lack or delay in flocculation can cause filtration difficulties and some problems in obtaining a bright sparkling beer; in addition, the presence of excess yeast in beer during ageing can cause off flavours due to yeast autolysis. Despite this commercial interest, limited information is available about the onset of flocculation and the various factors that may be responsible in the process. In particular, what are the signals that trigger flocculation? Adhesion properties applicable in improving yeast biotechnology are dependent directly or indirectly on characteristics of cellular surfaces, usually the outer layer of the cell wall. Change in the structure and or composition of the cell wall leads to changes in the microbial adhesion properties. Exploring more into the cell wall and studying the nanoscale structure of the yeast cell wall would thus be beneficial to augment our understanding of flocculation.

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4

Rossouw, Debra. "Comparative 'omic' profiling of industrial wine yeast strains". Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1454.

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Thesis (PhD(Agric) Viticulture and Oenology. Wine Biotechnology))--University of Stellenbosch, 2009.
The main goal of this project was to elucidate the underlying genetic factors responsible for the different fermentation phenotypes and physiological adaptations of industrial wine yeast strains. To address this problem an ‘omic’ approach was pursued: Five industrial wine yeast strains, namely VIN13, EC1118, BM45, 285 and DV10, were subjected to transcriptional, proteomic and exometabolomic profiling during alcoholic fermentation in simulated wine-making conditions. The aim was to evaluate and integrate the various layers of data in order to obtain a clearer picture of the genetic regulation and metabolism of wine yeast strains under anaerobic fermentative conditions. The five strains were also characterized in terms of their adhesion/flocculation phenotypes, tolerance to various stresses and survival under conditions of nutrient starvation. Transcriptional profiles for the entire yeast genome were obtained for three crucial stages during fermentation, namely the exponential growth phase (day 2), early stationary phase (day 5) and late stationary phase (day 14). Analysis of changes in gene expression profiles during the course of fermentation provided valuable insights into the genetic changes that occur as the yeast adapt to changing conditions during fermentation. Comparison of differentially expressed transcripts between strains also enabled the identification of genetic factors responsible for differences in the metabolism of these strains, and paved the way for genetic engineering of strains with directed modifications in key areas. In particular, the integration of exo-metabolite profiles and gene expression data for the strains enabled the construction of statistical models with a strong predictive capability which was validated experimentally. Proteomic analysis enabled correlations to be made between relative transcript abundance and protein levels for approximately 450 gene and protein pairs per analysis. The alignment of transcriptome and proteome data was very accurate for interstrain comparisons. For intrastrain comparisons, there was almost no correlation between trends in protein and transcript levels, except in certain functional categories such as metabolism. The data also provide interesting insights into molecular evolutionary mechanisms that underlie the phenotypic diversity of wine yeast strains. Overall, the systems biology approach to the study of yeast metabolism during alcoholic fermentation opened up new avenues for hypothesis-driven research and targeted engineering strategies for the genetic enhancement/ modification of wine yeast for commercial applications.

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Louw, Campbell (Campbell Trout). "The development of polysaccharide degrading wine yeast strains". Thesis, Stellenbosch : University of Stellenbosch, 2004. http://hdl.handle.net/10019.1/16382.

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Thesis (MSc)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: The polysaccharides that are present in wine originate from the grapes, the fungi that grow on the grapes and from other microorganisms that come into contact with the must during winemaking. The grape-derived polysaccharides of most concern in winemaking are pectin, glucan and xylan that can be enzymatically degraded by pectinases, glucanases and xylanases, respectively. These are the main structural polysaccharides of the cell wall of the grape cell. Degradation of the cell walls will result in the separation and rupture of the grape cells, and cell wall-bound compounds will be released into the must. Treating the must with pectinase and macerating enzyme preparations can result in an increase in free-flow juice, an improvement in must clarification and filtration, and an increased extraction of phenols and tannins. The tannins that are extracted polymerise with anthocyanins in red wine during ageing, resulting in increased colour intensity and stability. Wine aroma is also influenced by enzyme treatment. The degradation of the cell wall contributes to the release of glycosidically-bound terpene or alcohol precursors from the berries. The hydrolysis of these precursors during fermentation can result in an improvement in aroma. It can thus be seen that it is possible to improve wine quality and processing by supplementing the endogenous enzymes that are present in the fermentation with commercial enzyme preparations. Commercial enzymes are typically crude fungal preparations. The majority of commercial pectinase and glucanase preparations are derived from Aspergillus and Trichoderma, respectively. Since the endogenous polysaccharase activity of Saccharomyces cerevisiae is very limited, the heterologous expression of specific polysaccharase genes in an industrial yeast strain can improve the winemaking process, resulting in a higher quality wine without the addition of expensive commercial enzyme preparations. Since only the desired enzymes are secreted by the recombinant strain, there will be no undesired sideactivities, which can be detrimental to wine quality. Several pectinase-, glucanaseand xylanase-encoding genes, cloned from a variety of organisms, have been expressed successfully in laboratory strains of S. cerevisiae. Attempts have also been made to construct industrial wine yeast strains that express these polysaccharase genes and secrete the encoded enzymes. Fermentation with some of these strains resulted in a decrease in total phenolics and turbidity, an increase in juice extraction, and alterations in the colour and aromatic profile of the resulting wines. In this study, four polysaccharide-degrading, recombinant wine yeast strains were constructed. The endo-β-1,4-xylanase gene, XYN2, and the endo-β-1,4-glucanase gene, end1, were previously cloned from the soft rot fungus Trichoderma reesei and the rumen bacterium Butyrivibrio fibrisolvens, respectively. These genes were subcloned into different expression cassettes which were used to construct the four integration plasmids. The recombinant plasmids contained the following gene cassettes: TEF1P-XYN2-ADH2T (plasmid pDLG29) ADH1P- MFα1S -end1-TRP5T (plasmid pDLG30) ADH1P-MFα1S-end1-TRP5T and ADH2P-XYN2-ADH2T (plasmid pDLG33), ADH1P-MFα1S-end1-TRP5T and YG100PXYN2- ADH2T (plasmid pDLG39). These four plasmids were then separately integrated into the ILV2 locus of the commercial wine yeast strain S. cerevisiae VIN13. Wine was made with the four strains constructed in this study, a pectolytic strain, VIN13[pPPK], a glucanase- and xylanase-secreting strain, VIN13[pEX], an untransformed VIN13 strain, and an untransformed strain with the addition of the commercial enzyme preparation Rapidase EX Colour. Microvinification experiments were carried out on Pinot noir, Ruby Cabernet and Muscat d’Alexandria wines. Fermentation with the polysaccharide-degrading strains resulted in significant improvements in juice extraction, colour intensity and stability, and in alterations in the aromatic profiles of the wines produced. Subject to the approval by the regulatory authorities and eventual consumer acceptance of the use of genetically modified organisms (GMOs) in fermented foods and beverages, it might be required that the GM status of the yeast that is used appears on the label. Currently, there is no robust technique available with which the use of GM yeast can be revealed in a finished wine because the yeast cells and their DNA are removed from or denatured in the wine during filtration and processing. One way with which the undeclared use of a GM yeast in winemaking could be exposed would be to compare the chemical profile of a suspect wine with that of non-GM wine. In order to explore this concept further, a secondary aim of this study was to investigate whether Fourier Transformation Infra Red (FT-IR) spectroscopy coupled with multivariate data analysis could distinguish between wines fermented with transgenic and non-transgenic yeast strains, or between wines fermented with different transgenic strains. The results showed that this method could be used to classify wines fermented with different yeast strains if fermentation with the strain resulted in a unique chemical profile in the resulting wine. This was a preliminary study and these findings were summarised as an addendum to the thesis.
AFRIKAANSE OPSOMMING: Die polisakkariede wat in wyn teenwoordig is, is afkomstig van die druiwe, die swamme wat op die druiwe groei en vanaf ander mikroörganismes wat tydens die wynmaakproses met die mos in aanraking kom. Die belangrikste druifpolisakkariede in wynbereiding is pektien, glukaan en xilaan, wat onderskeidelik deur pektinases, glukanases en xilanases afgebreek kan word. Hierdie is die vernaamste strukturele polisakkariede van ‘n druifsel se selwand. Die afbreking van die selwande veroorsaak dat die druifselle skei en skeur, met die gevolg dat die selwandgebonde verbindings in die mos vrygelaat word. Die behandeling van die mos met pektinase en versappingsensiempreparate kan tot ŉ toename in vry-afloopsap lei, sowel as ŉ verbetering in mosverheldering en -filtrasie en ŉ verhoogde ekstraksie van fenole en tanniene. Die tanniene wat geëkstraheer word, polimeriseer in rooiwyn tydens veroudering, en dit lei tot verhoogde kleurintensiteit en -stabiliteit. Wynaroma word ook deur ensiembehandeling beïnvloed. Die afbreking van die druifselwand dra by tot die vrylating van glikosidiesgebonde terpeen- en alkoholvoorlopers uit die korrels. Die hidrolise van hierdie voorlopers tydens gisting kan lei tot ŉ verbetering van die aroma. Dit is dus duidelik dat dit moontlik is om wynkwaliteit en wynbereiding te verbeter deur die endogene ensieme wat in die gisting teenwoordig is met kommersiële ensiempreparate te supplementeer. Kommersiële ensiempreparate is tipies ongesuiwerde swampreparate. Die meerderheid kommersiële pektinase- en glukanasepreparate word onderskeidelik vanaf Aspergillus en Trichoderma verkry. Aangesien die endogene polisakkaraseaktiwiteit van Saccharomyces cerevisiae baie beperk is, kan die heteroloë uitdrukking van spesifieke polisakkarase-gene in ŉ industriële gisras die wynbereidingsproses verbeter en lei tot ŉ hoër kwaliteit wyn sonder die byvoeging van duur kommersiële ensiempreparate. Omdat die verkose ensieme deur die rekombinante ras uitgeskei word, sal daar geen ongewenste newe-effekte teenwoordig wees wat ŉ nadelige effek op wynkwaliteit kan hê nie. Verskeie mikrobiese gene wat vir pektinases, glukanases en xilanases kodeer, is reeds voorheen uit ‘n wye verskeidenheid van organismes gekloneer en suksesvol in laboratoriumrasse van S. cerevisiae uitgedruk. Pogings is ook aangewend om industriële wyngisrasse te konstrueer wat hierdie polisakkarasegene uitdruk en hul enkodeerde ensieme uitskei. Gisting met sommige van hierdie rekombinante gisrasse het gelei tot ŉ afname in totale fenoliese verbindings en troebelheid, ŉ verhoging in sapekstraksie, en veranderings in die kleur en aromatiese profiel van die gevolglike wyne. In hierdie studie is vier polisakkaried-afbrekende, rekombinante wyngisrasse gekonstrueer. Die endo-β-1,4-xilanasegeen, XYN2, en die endo-β-1,4- glukanasegeen, end1, is voorheen reeds onderskeidelik vanaf die sagte vrotswam, Trichoderma reesei, en die rumenbakterium, Butyrivibrio fibrisolvens, gekloneer. Hierdie gene is in vier integrasieplasmiede in verskillende ekspressiekassette gesubkloneer. Die plasmiede het die volgende geenkassette bevat: TEF1P-XYN2- ADH2T (plasmied pDLG29) ADH1P- MFα1S -end1-TRP5T (plasmied pDLG30) ADH1PMFα1S- end1-TRP5T and ADH2P-XYN2-ADH2T (plasmied pDLG33), ADH1P-MFα1S end1-TRP5T and YG100P-XYN2-ADH2T (plasmied pDLG39). Hierdie vier plasmiede is toe afsonderlik in die ILV2-lokus van die kommersiële wyngisras, S. cerevisiae VIN 13, geïntegreer. Wyn is met hierdie vier gekonstrueerde gisrasse gemaak, die pektolitiese gisras, VIN13[pPPK], die glukanase- en xilanase-afskeidende gisras, VIN13[pEX], die ongetransformeerde VIN13-ras, en met ŉ ongetransformeerde VIN13 gis waarby die kommersiële ensiempreparaat, Rapidase EX Colour, bygevoeg is. Mikro-wynbereidingseksperimente is op Pinot noir-, Ruby Cabernet- en Muscat D’Alexandria wyne uitgevoer. Gisting met die polisakkaried-afbrekende gisrasse het gelei tot ŉ noemenswaardige verbetering in sapekstraksie, kleurintensiteit en kleurstabiliteit, asook in veranderinge in die aromatiese profiele van die geproduseerde wyne. Indien die gebruik van geneties gemodifiseerde organismes (GMOs) in gefermenteerde voedsel en drank deur die reguleringsowerhede goedgekeur en uiteindelik deur die verbruiker aanvaar sou word, sou dit vereis kon word dat die GMstatus van die wyngisgis op die etiket van die wynbottel aangebring word. Verpligte etikettering van GM-wyn sal metodes vereis waarmee die ‘nalentskap’ van GMgisselle in die finale produk geïdentifiseer en gemoniteer kan word. Tans is daar geen robuuste tegnieke beskikbaar waarmee die gebruik van GM-giste openbaar kan word nie, aangesien die gisselle en hul DNA tydens filtrasie en prosessering verwyder word. Een wyse waarop die onverklaarde gebruik van ‘n GM-gis in wynbereiding blootgestel sou kno word, is om die chemiese profiel van die verdagte wyn met dié van ‘n nie-GM-wyn te vergelyk. Ten einde hierdie konsep verder te ondersoek was ‘n sekondêre doelwit van hierdie studie om te bepaal of FT-IR (Fourier-transformasie-infrarooi) spektroskopie tesame met meervariante dataanalise gebruik kan word om te onderskei tussen wyne wat met transgeniese en nietransgeniese gisrasse gegis is, of tussen wyne wat met verskillende transgeniese rasse gegis is. Die resultate het aangedui dat hierdie metode gebruik kan word om wyne wat met verskillende gisrasse gegis is, te klassifiseer indien die betrokke gisras ŉ unieke chemiese profiel in die uiteindelike wyn veroorsaak het. Dit was egter ŉ voorlopige ondersoek en is as ŉ byvoegsel tot die tesis geskryf.

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6

Hemmati, Naghmeh. "Engineering yeast strains to enhance bioethanol production efficiency /". Available to subscribers only, 2008. http://proquest.umi.com/pqdweb?did=1674956301&sid=4&Fmt=2&clientId=1509&RQT=309&VName=PQD.

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7

Mocke, Bernard A. "The breeding of yeast strains for novel oenological outcomes". Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/1117.

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8

Zelena, L., S. Nevmyvaka e I. Hretskyi. "Effect of co-culturing yeast strains on cell density". Thesis, Київський національний університет технологій та дизайну, 2020. https://er.knutd.edu.ua/handle/123456789/15572.

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9

Trollope, Kim. "Investigation of resveratrol production by genetically engineered Saccharomyces cervisiae strains /". Link to the online version, 2006. http://hdl.handle.net/10019/1247.

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10

Boeira, Lucia Schuch. "Effects of fusariotoxins on the performance of brewing yeast strains". Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/560.

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11

Ndlovu, Thulile. "Mannoprotein production and wine haze reduction by wine yeast strains". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71938.

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Thesis (PhD)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: Wine protein haze formation is a major challenge for wine makers, and several wine clarifying agents such as bentonite are used in the industry to protect wine from this occurrence. However, clarifying agents may have an undesirable impact on wine quality. Yeast mannoproteins have been shown to possess haze-protective properties, while also positively impacting on the sensorial properties of the product. However, while such mannoproteins are released into the wine during the wine making process, the amounts are low and therefore of limited oenological significance. However, and although commercial wine yeast strains display significant genotypic and phenotypic diversity, no broader assessment of haze protective activity and of mannoproteins release by different wine yeast strains has been undertaken. In this study, several yeast strains were screened for their impact on wine haze formation in Chardonnay must and in a grape juice model system. The data show that strains of the species Saccharomyces paradoxus possess better haze protective properties than the common Saccharomyces cerevisiae wine yeast strains. Differences in the nature of the proteins released by these two species were investigated, and indicated that several mannoproteins were released at significantly higher levels by S. paradoxus, and that some of these proteins might indeed contribute to the haze-protective activity. A further exploration of yeast cell wall properties indicated that the cell walls of haze-protective S. paradoxus strains contained higher levels of chitin than non-haze protective strains. Grape chitinases are likely to be primarily responsible for wine haze formation, and the data clearly demonstrate that these enzymes are able to bind to the yeast cell walls, and that strains with higher amounts of chitin in the cell wall will bind more chitinases. This finding suggests that the haze-protective nature of the strains is at least in part linked to the chitin levels of the strains. Furthermore, the impact of some genetic modifications in two wine strains (namely S. cerevisiae VIN13 and S. paradoxus RO88) suggests that several proteins contribute to wine haze protection. However, none of the mannoprotein-encoding flocculation genes, FLO1, FLO5, and FLO11 showed any impact on this property. Further studies are required to assess the full impact of the S. paradoxus strains on haze protection. In particular, the possible use of such strains as starter cultures or the use of S. paradoxus yeast hulls as clarifying agent needs to be further explored.
AFRIKAANSE OPSOMMING: Wyn proteïen-waas vorming is 'n groot uitdaging vir wynmakers en verskeie wyn verhelderings agente soos bentoniet word in die wynbedryf gebruik om wyn te beskerm teen die vorming van waas. Hierdie verheldering agente het egter 'n ongewenste impak op wynkwaliteit. Gis mannoproteïene is uitgewys as proteïene met moontlike waas-beskermende eienskappe wat ook 'n positiewe uitwerking op die sensoriese eienskappe van die produk het. Al word hierdie mannoproteïene egter vrygestel in die wyn tydens die wynmaak proses, is die hoeveelhede oor die algemeen te laag om van wynkundige belang te wees. Verder, ten spyte van die beduidende genotipiese en fenotipiese diversiteit van kommersiële wyngisrasse is daar nog geen breër assessering van die waas beskermende aktiwiteit van mannoproteïene, vrygestel deur verskillende rasse, tot dusver onderneem nie. In hierdie studie is verskeie gisrasse gekeur vir hul impak op wyn waas-vorming in Chardonnay mos en ook in 'n model druiwesap. Die data wys dat rasse van die spesie Saccharomyces paradoxus besit beter waas beskermende eienskappe as die algemene Saccharomyces cerevisiae wyngisrasse. Verskille in die aard van die proteïene wat vrygestel is deur hierdie twee spesies is ondersoek, en dit is aangedui aangedui dat verskeie mannoproteins vrygestel aan aansienlik hoër vlakke deur S. Paradoxus. Dit is ook aangedui dat sommige van hierdie proteïene wel bydra tot die waas-beskermende aktiwiteit. 'n Verdere verkenning van gis selwand eienskappe het aangedui dat die selwande van waas-beskermende rasse van S. paradoxus hoër vlakke chitien as nie-waas beskermende stamme bevat. Druiwe chitinases is waarskynlik hoofsaaklik verantwoordelik vir wyn waas vorming, en die data toon duidelik dat hierdie ensieme in staat is om te bind aan die gis selwande, en dat die stamme met hoër vlakke chitien in die selwand meer chitinases sal bind. Hierdie bevinding dui daarop dat die waas-beskermende aard van die stamme ten minste gedeeltelik gekoppel is aan die chitien vlakke van die stamme. Die impak van sekere genetiese modifikasies in twee verskillende gisrasse, naamlik die S. cerevisiae ras VIN13 en die S. paradoxus ras RO88, dui verder daarop dat verskeie proteïene dra by tot die beskerming teen wyn waas. Geeneen van die mannoprotein-koderende flokkulasie gene, FLO1, FLO5 en FLO11 het egter 'n impak op hierdie eienskap nie. Verdere studies is nodig om die volle impak van die S. paradoxus rasse op waas beskerming te assesseer. In die besonder, die moontlike gebruik van sulke rasse as 'n inkolasie kultuur of die gebruik van S. paradoxus gis doppe as verheldering agent moet verder ondersoek word.

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Hall, Nichola. "The influence of zinc on the physiology of industrial strains of Saccharomyces cerevisiae". Thesis, Abertay University, 2001. https://rke.abertay.ac.uk/en/studentTheses/f84e16c0-c175-46aa-ad63-474107be7130.

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The yeast, Saccharomyces cerevisiae requires certain elements for the growth and development of healthy cultures. The divalent cation, zinc is of paramount importance to this yeast, as zinc is a structurally and functionally essential metal that cannot be replaced by any other element. Zinc accumulation by S. cerevisiae is a biphasic response, consisting of a rapid metabolism independent and a metabolism dependent phase. Metabolism-independent metal ion accumulation is a physical process, whereby the ions are associated with the cell wall. This stage of uptake is often referred to as biosorption and zinc uptake is influenced by temperature, pH, biomass concentration and the presence of competing ions. The second phase of zinc uptake (metabolism-dependent metal ion accumulation) concerns the intracellular accumulation of the ions. This biological accumulation, often abbreviated to bioaccumulation, is slower than biosorption as the zinc ions are transported into the cell, via the plasma membrane by the energy consuming process, active transport. The presence and type of metabolisable energy source, metabolic inhibitors, as well as the factors that affect biosorption also affect bioaccumulation. The genetics governing zinc accumulation by S. cerevisiae has recently been unravelled (Zhao and Eide, 1996a & b). Research has shown that a high (ZRT1) and a low (ZRT2) affinity transporter proteins exists, which act in zinc limiting and zinc replete conditions, respectively. Once the transporters aid zinc uptake into the cell, this important divalent cation is either utilised immediately or compartmentalised in the vacuole until required. Zinc accumulation is influenced by yeast cell physiology. Upon examination of zinc uptake with respect to cell growth, in various metabolisable energy sources, the results demonstrate that zinc is influential in the growth of industrial relevant strains of S. cerevisiae, and that zinc accumulation is affected by the presence and type of metabolisable energy source e.g. glucose, fructose, maltose and sucrose. Optimal growth was achieved when the lager yeast and wine yeast was grown in a minimal media containing sucrose as the metabolisable energy source after a 24 hour period with distillers yeast and bakers yeast growth was maximum when grown for 24 hours in a fructose supplemented media. The industrial strains of yeast studied appeared to sequester maximum zinc when the YPDM was supplemented with monosaccharides, as opposed to disaccharide, after a 24 hour examination period. The accumulation of zinc by S. cerevisiae lager yeast is a cyclical event with uptake occurring during lag and early exponential phase of growth, with zinc appearing to convey a protective effect on cells which have been subjected to a chemical (15% ethanol) and a physical (heat shock- 45°C) stress. The influence of zinc accumulation on yeast cell physiology was studied with respect to specific enzyme (Alcohol Dehydrogenase) and metabolite (ethanol) production. The results demonstrate a general trend, with more ADH produced when the cells have sequestered more zinc, this in turn had a positive effect on the overall ethanol production of a strain of lager yeast.

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Nair, Pradeep. "Analysis of mating defective yeast strains isolated from a novel screen". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0021/NQ51907.pdf.

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14

Morgenroth, Olaf. "Evaluating ethanol yields of wine yeast strains under various fermentative conditions". Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86379.

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Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: The market for high quality lower alcohol wines is growing globally. Several factors are responsible for this trend, with socio-economic and health concerns being considered as being the most relevant. It is therefore no surprise that in the past three decades many systems have been developed to reduce wine ethanol levels, each with its own strengths and weaknesses. However, current systems are not always cost effective and frequently result in unwanted side-effects. Microbiological methods primarily based on redirecting carbon flux in existing, or novel Saccharomyces and non-Saccharomyces yeast strains, might have the potential to eliminate or reduce such shortcomings. However, little base-line information regarding differences in ethanol yields of existing wine yeast strains, and on the impact of fermentation conditions on such yields is currently available. In this study the ethanol yield of 15 wine yeast strains was investigated in synthetic wine must under varied wine fermentative conditions including changes in yeast assimilable nitrogen, sugar concentration, pH and fermenting temperatures to identify strains that produce lower ethanol yields and conditions that would favour such an outcome. Most strains and conditions resulted in very similar ethanol yields, however in some cases interesting differences were observed. Some of the strains showed significant differences between high and low nitrogen containing must. Results from synthetic must were confirmed in grape must (Sauvignon Blanc, Chardonnay, Shiraz and Cabernet Sauvignon), but no consistent response could be observed. Interestingly the Shiraz fermentations always showed a higher ethanol yield for all strains investigated. This may be due to a parameter (or combination thereof) which was not included as an experimental factor in our study. Glycerol yield was also studied in the grape must experiments and was found to be more significantly condition dependent than ethanol yield. Temperature and glycerol seemed to be directly proportional confirming the results of previous studies. While temperature did increase glycerol production, it was concluded that the redirection of carbon towards glycerol was not substantial enough to have measurable effect on the final ethanol concentration. The most notable differences which were observed were very specific to a particular yeast strain and condition pairing, thus no generally applicable treatment to achieve lower ethanol yields could be established.
AFRIKAANSE OPSOMMING: Deesdae is daar ‘n groeiende mark vir lae alkohol wyne van hoë gehalte. Verskeie faktore is verantwoordelik vir hierdie verskynsel, met sosio-ekonomiese en gesondheidskwessies as die hoof rolspelers. Vir hierdie rede is daar gedurende die laaste drie dekades baie stelsels ontwikkel om wyn etanol vlakke te verlaag, elkeen met voor- en nadele. Meeste van die huidige stelsels is nie koste effektief nie en lei gewoonlik tot ongewenste newe effekte. Mikrobiologiese metodes wat gebaseer is op koolstof vloei veranderinge in wyn gisrasse mag die potensiaal bied om hierdie tekortkominge te verminder of te oorbrug. ‘n Alternatief is om nuwe Saccharomyces en nie-Saccharomyces gisrasse te identifiseer wat laer etanol opbrengste lewer. In hierdie studie is die etanol opbrengste van 15 wyn gisrasse ondersoek in ‘n sintetiese mos in verskeie toestande, bv. veranderde stikstof vlakke, suiker vlakke, pH en temperatuur, om die rasse te identifiseer wat laer etanol opbrengste lewer (asook die toestande wat laer etanol opbrengste bevorder). Meeste rasse en toestande het soortgelyke etanol opbrengste getoon, alhoewel daar in sekere gevalle interessante verskille was rakende sekere rasse wat verskillende resultate lewer in mos met verskillende stikstof vlakke. Die resultate van die sintetiese mos eksperimente was bevestig in druiwe mos van vier kultivars (Sauvignon Blanc, Chardonnay, Shiraz en Cabernet Sauvignon), maar geen algemene tendens kon afgelei word nie. Wat interessant was is die feit dat die Shiraz fermentasies altyd hoër etanol opbrengste gelewer het vir al vier gisrasse wat gebruik is vir hierdie eksperimente. Dit mag wees weens ‘n eksperimentele faktor wat nie bestudeer was in die raamwerk van hierdie projek nie. Die opbrengs van gliserol was ook bepaal in die verskeie eksperimente en daar was gevind dat gliserol opbrengs baie meer kondisie-afhanklik is in vergelyking met etanol. Temperatuur en gliserol het ‘n direkte verbandskap met mekaar getoon, wat die bevindinge van vorige studies bevestig. Alhoewel verhogings in temperatuur wel gliserol produksie vermeerder het, was die effek nie genoeg om ‘n meetbare impak op die finale etanol konsentrasie te hê nie. Verskillende giste in verskeie verskillende fermentasie toestande het soortgelyke etanol opbrengste gelewer. Die mees merkbare verskille wat bevind is was spesifiek tot individuele gisras en kondisie kombinasies, maar geen algemene afleiding kon gemaak word rakende behandelings wat etanol opbrengste kan verlaag nie.

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15

Groß, Annett. "Genetically Tailored Yeast Strains for Cell-based Biosensors in White Biotechnology". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-83341.

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This work was performed in the framework of two application-oriented research projects that focus on the generation and evaluation of fluorescent Saccharomyces (S.) cerevisiae-based sensor and reporter cells for white biotechnology as well as the extension of the conventional single-cell/single-construct principle of ordinary yeast biosensor approaches. Numerous products are currently generated by biotechnological processes which require continuous and precise process control and monitoring. These demands are only partially met by physical or physiochemical sensors since they measure parameters off-line or use surrogate parameters that consequently provide only indirect information about the actual process performance. Biosensors, in particular whole cell-based biosensors, have the unique potential to near-line and long-term monitor parameters such as nutrient availability during fermentation processes. Moreover, they allow for the assessment of an analyte’s biological relevance. Prototype yeast sensor and reporter strains derived from common laboratory strains were transformed with multicopy expression plasmids that mediate constitutive or inducible expression of a fluorescence reporter gene. Performance of these cells was examined by various qualitative and quantitative detection methods – representative of putative transducer technologies. Analyses were performed on the population level by microplate reader-based fluorometry and Western blot as well as on the single-cell level by fluorescence microscopy and flow cytometry. ‘Signature’ promoters that are activated or repressed during particular nutrient-limited growth conditions were selected in order to generate yeast nutrient sensor strains for monitoring the biological availability of nitrogen, phosphorus or sulphur. For each category, at least one promoter mediating at least threefold changed green fluorescence levels between sensor cells in non-limited and nutrient-limited conditions was identified. Sensor strains were evaluated in detail regarding sensitivity, analyte selectivity and the ability to restore basic fluorescence after shift from nutrient-limited to non-limited conditions (regeneration). The applicability for bioprocess monitoring purposes was tested by growth of yeast nutrient sensor cells in microalgae media and supernatants. Despite successful proof of principle, numerous challenges still need to be solved to realise prospective implementation in this field of white biotechnology. The major drawback of plasmid-borne detection constructs is a high fluorescence variance between individual cells. By generation of a nitrogen sensor strain with a genome-integrated detection construct, uniform expression on the single-cell level and simultaneous maintenance of basic properties (ability of fluorescence induction/regeneration and lack of cross-reactivity) was achieved. However, due to the singular detection construct per cell, significantly weaker overall fluorescence was observed. The traditional single-cell/single-construct approach was expanded upon in two ways. Firstly, a practical dual-colour sensor strain was created by simultaneous, constitutive expression of a red fluorescence reporter gene in green fluorescent nitrogen sensor cells. Secondly, an innovative cellular communication and signal amplification system inspired by the natural S. cerevisiae pheromone system and mating response was established successfully. It features the yeast pheromone alpha-factor as a trigger and alpha-factor-responsive reporter cells which express a fluorescence reporter gene from the pheromone-inducible FIG1 promoter as an output signal. The system was functional both with synthetic and cell-secreted alpha-factor, provided that recombinant cells were deleted for the alpha-factor protease Bar1p. Integration of amplifier cells which secrete alpha-factor in response to stimulation with the pheromone itself could increase the system\'s sensitivity further. Signal amplification was demonstrated for phosphorus sensor cells as a proof of concept. Therefore, the alpha-factor-based cellular communication and signal amplification system might be useful in applications that suffer from poor signal yield. Due to its modular design, the system could be applied in basically any cell-based biosensor or sensor-actor system. Immobilisation of the generated sensor and reporter cells in transparent natural polymers can be beneficial considering biosensor fabrication. Functionality of sensor and reporter cells in calcium-alginate beads or nano-printed arrays was successfully demonstrated. For the latter setup, fluorescence scanning and software-assisted fluorescence quantification was applied as a new detection method. In an experiment using an agarose-based two-compartment setup proposed by Jahn, 2011, properties of the alpha-factor-based cellular communication and signal amplification system after immobilisation were tested. These studies provide an initial experimental basis for an appropriate geometry of miniaturised immobilisation matrices with fluorescent yeast sensor and reporter cells in prospective biosensor designs.

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16

Osborne, Charles D. "Discriminating wine yeast strains and their fermented wines : an integrated approach". Thesis, Link to the online version, 2007. http://hdl.handle.net/10019/699.

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17

Yip, Hopi, of Western Sydney Hawkesbury University e Faculty of Science and Technology. "Genetic manipulation of baker's yeast for improved maltose utilisation". THESIS_FSTA_SFS_Yip_H.xml, 1999. http://handle.uws.edu.au:8081/1959.7/223.

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Two yeast/E.coli shuttle vector plasmids were studied in 1994, termed pIBIDB and pBP33. According to this study, each plasmid should contain at least one ADH2UAS (upstream activation sequence in the alcohol dehydrogenase 2 gene) insert. In the present study, the constructed plasmids were analysed and transformed into laboratory strain yeast. The aim of this project was to identify the orientation, quantity and quality of the insert in the selected plasmids. Methods such as restriction analysis, polymerase chained reaction (PCR), sequencing, plate assays and enzyme assays were used to identify and evaluate the novel inserts. The data presented in this thesis suggest the inserted ADH2UAS fragment did enhance the production of maltose permease and maltase when the transformants were cultivated in maltose and ethanol-glycerol medium. The results suggested that transformants containing two inserts of ADH2UAS had a greater influence on the transformants than a single insert. But the inserts within the vectors and in transformed laboratory stain yeast appeared unstable. This could be due to the method used for plasmid construction and the storage condition of the transformants
Master of Science (Hons)

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18

Bowen, Suzanne. "Stress and stationary phase characteristics in cell wall defective strains of Saccharomyces cerevisiae". Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341199.

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19

Trollope, Kim. "Investigation of resveratrol production by genetically engineered Saccharomyces cerevisiae strains". Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/2230.

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Thesis (MSc (Wine Biotechnology))--University of Stellenbosch, 2006.
Resveratrol is a phytoalexin that is produced in the leaves and skins of grape berries in response to biotic and abiotic factors. Substitution and polymerisation of resveratrol units produce an array of compounds which form part of the active disease defence mechanism in grapevine. Wine is one of the major sources of resveratrol in the human diet. Resveratrol is one of the phenolic compounds present in wine that mediates protective effects on human health. It has been shown to prevent the development of cardiovascular disease, cancer and pathogenesis related to inflammation. Red wines contain higher levels of resveratrol than white wines owing to extended maceration times during fermentation on the skins. During white wine vinification skin contact is limited as skins are removed prior to fermentation. Thus, the extraction of resveratrol into white wines is minimal. The principal focus of our research is the development of a wine yeast strain capable of resveratrol production during grape must fermentation. It is proposed that red and white wines produced with such a resveratrol-producing yeast will contain elevated levels of resveratrol, and that added health benefits may be derived from their consumption. Initial work done in our laboratory established that expressing multiple copies of the genes encoding coenzyme A ligase (4CL216) and resveratrol synthase (vst1) in laboratory yeast enabled the yeast to produce resveratrol, conditional to the supplementation of the growth medium with p-coumaric acid. This study focused on the optimisation of resveratrol production in Saccharomyces cerevisiae. It involved the integration and constitutive expression of 4CL216 from hybrid poplar and vst1 from grapevine. Integration and expression of these genes in three laboratory strains was confirmed by Southern and Northern blot analyses. The evaluation of resveratrol production by yeast required the initial optimisation of the analytical techniques. We optimised the method for sample preparation from the intracellular fraction of yeast and devised a procedure for the assay of the extracellular fractions. The LCMSMS method was further developed to encompass detection and quantification of other compounds related to resveratrol production in yeast. Comparison of resveratrol production in three different yeast genetic backgrounds indicated that the onset of production and the resveratrol yield is yeast strain dependent. Precursor feeding studies indicated that p-coumaric acid availability was a factor limiting maximal resveratrol production. Early indications were obtained that endogenously-produced resveratrol may have an impact on yeast viability during extended culture periods. This study has broadened our understanding of the resveratrol production dynamics in S. cerevisiae and provided important indications as to where further optimisation would be beneficial in order to optimally engineer a wine yeast for maximal resveratrol production.

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20

Zou, Wen. "STUDIES ON THE NEW FUNCTIONAL YEAST STRAINS CONSTRUCTED AND SCREENED BY CELL SURFACE ENGINEERING". 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150264.

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21

Chlup, Paul H. "Biological and hydrodynamic stress influences on brewing yeast strains' physiological status during beer production". Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2195.

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Biological hydrodynamic stress influences on yeast and the resulting consequences on beer stability have been investigated. Yeast cells subjected to stress during beer production have a negative effect on its physiological status. Cell wall and membrane constituents determine the cells capacity to adapt to stress. A relationship has been established that yeast cell wall mannan, an unfilterable haze constituent, as a function of hydrodynamic stress exposure, is released from the cell wall while concurrently, particle size in the supernatant, and beer haze increased. In high gravity wort (20 °Plato), compared to lower gravity wort (12 °Plato), there is an increase in the number of damaged cells and lower intracellular glycogen and trehalose levels, indicating stressed cells. Cell viability and intracellular pH decreased due to processing conditions encountered during yeast cropping with a centrifuge. Furthermore, yeast intracellular glycogen and trehalose levels were depleted as a result of centrifugation. A comprehensive evaluation of yeast fermentation predictors such as viability, damaged cells, intracellular pH (PHi), intracellular glycogen and trehalose is of vital importance. The flow cytometer is able to rapidly reform numerous accurate yeast physiology analyses, providing information that will optimize yeast management circuits, improve fermentation efficiency resulting in enhanced beer quality.

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22

Jolly, N. P. (Neil Paul). "Characterisation, evaluation and use of non-Saccharomyces yeast strains isolated from vineyards and must". Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/49877.

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Dissertation (PhD)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Wine is the product of a complex biological and biochemical interaction between grapes and different microorganisms (fungi, yeasts, lactic acid bacteria and acetic acid bacteria, as well as the mycoviruses and bacteriophages affecting them) in which yeasts play the most important role regarding the alcoholic (primary) fermentation. These wine-associated yeasts can be divided into Saccharomyces and non-Saccharomyces yeasts. During fermentation, there is a sequence of dominance by the various non-Saccharomyces yeasts, followed by Saccharomyces cerevisiae, which then completes the fermentation. This is especially evident in spontaneously fermenting must, which has a low initial S. cerevisiae concentration. Some non- Saccharomyces yeasts can also be found throughout the fermentation. The non- Saccharomyces presence in the fermentation can affect wine quality, either positively or negatively. A positive contribution could be especially useful to improve wines produced from grape varieties with a neutral flavour profile due to non-optimal climatic conditions and/or soil types. As part of a comprehensive South African research programme, the specific objectives of this study were: the isolation of indigenous non-Saccharomyces yeasts from vineyards and musts; the identification of these isolates; the characterisation and evaluation of predominant species under winemaking conditions; and the development of a protocol for their use in enhancing wine quality. Initially, 720 isolates representing 24 different species, were isolated from grape (vineyard) and must samples taken over three vintages from four distinctly different wine producing regions. The isolates were characterised and grouped utilising biochemical profiles and DNA karyotyping, whereupon representative isolates were identified. The yeast species that had the highest incidence of predominance in the vineyard was Kloeckera apiculafa. However, some vineyard samples were characterised by low numbers or absence of this yeast, which is not according to generally accepted norms. Other species that also predominated in a few of the vineyard samples were Candida pulcherrima, Kluyveromyces thermofolerans, Rhodotorula sp. and Zygosaccharomyces bailii. Generally, there was a greater diversity of yeasts in the processed must than from the vineyard samples. Furthermore, while each sample showed a different yeast population, no pattern linking species to climatic zone was observed. Four species i.e. Candida collieulosa, Candida pulcherrima, Candida stel/ata and Kloeckera apiculata, were found to predominate in grape must samples. Representative strains consequently received further attention during laboratory and small-scale winemaking trials. A protocol was developed whereby individual species could be used in co-inoculated fermentations with S. cerevisiae in the small-scale production of wine. An improvement in wine quality was achieved and it was found that there was a link between specific species and grape cultivar. The ability of C. pulcherrima to improve Chenin blanc wine quality was investigated further. Results over three vintages showed that the wine produced by the co-inoculated fermentation was superior to that of a reference wine (produced by S. cerevisiae only). The improvement in wine quality was not linked to increased ester content nor were the standard chemical analyses adversely affected. The effects of pH and wine production parameters i.e. 802, fermentation temperature and use of di-ammonium phosphate (DAP), on this yeast followed the same pattern as that known for S. cerevisiae. This study was successfully completed and the developed protocol can be used for the improvement of Chenin blanc wine where additional aroma and quality is needed.
AFRIKAANSE OPSOMMING: Wyn is die produk van 'n komplekse biologiese en biochemiese interaksie tussen druiwe en mikroorganismes (swamme, giste, melksuurbakterieë, asynsuurbakterieë, asook die mikovirusse en bakteriofage wat hul beïnvloed) waar gis die belangrikste rol speel ten opsigte van die alkoholiese (primêre) fermentasie. Die betrokke giste kan in Saccharomyces- en nie-Saccharomyces-giste verdeel word. Tydens gisting vind daar 'n opeenvolging van dominansie deur die verskillende nie-Saccharomyces giste plaas, gevolg deur Saccharomyces cerevisiae, wat dan die gisting voltooi. Dit is veral in spontaan fermenterende mos, waarin aanvanklik lae konsentrasies S. cerevisiae-gisselle voorkom, waarneembaar. Sekere nie-Saccharomyces-giste kan ook regdeur die verloop van fermentasie gevind word. Die teenwoordigheid van nie-Saccharomyces-giste kan 'n bydrae maak tot wynkwaliteit, hetsy positief of negatief. 'n Positiewe bydrae kan veral nuttig wees vir die verbetering van wyn geproduseer van druifsoorte met neutrale geurprofiele as gevolg van nie-optimale klimaatstoestande en/of grondtipes. As deel van 'n uitgebreide Suid-Afrikaanse navorsingsprogram, was die doelwitte van hierdie studie soos volg: die isolasie van inheemse nie-Saccharomyces-giste vanuit wingerde en mos; die identifikasie van hierdie isolate; die karakterisering en evaluering van spesies wat tydens wynbereiding oorheers; en die ontwikkeling van 'n protokol waarin geselekteerde nie- Saccharomyces-giste gebruik kan word vir die verbetering van wynkwaliteit. Druif- en mosmonsters is oor drie oestye vanuit vier duidelik onderskeibare wynproduserende gebiede geneem en 720 isolate, verteenwoordigend van 24 verskillende spesies, is hieruit geïsoleer. Hierdie isolate is volgens biochemiese profiele en DNA-kariotipering gekarakteriseer en gegroepeer waarna verteenwoordigende isolate geïdentifiseer is. Die gisspesie wat die meeste in wingerde voorgekom het, was Kloeckera apiculata. Sommige wingerde is egter deur lae getalle of afwesigheid van dié gis gekenmerk, In feit wat afwyk van die algemeen aanvaarde norm. Ander spesies, nl. Candida pulcherrima, Kluyveromyces thermotolerans, Rhodotorula sp. en Zygosaccharomyces bailii, het ook in enkele gevalle in die wingerdmonsters oorheers. Oor die algemeen was daar 'n groter diversiteit van giste in die geprosesseerde mos as in die wingerdmonsters. Verder is elke monster gekenmerk deur verskillende gispopulasies, maar geen verband tussen gisspesie en klimaatsone is waargeneem nie. Vier spesies, nl. Candida collieulosa, Candida pulcherrima, Candida stel/ata en Kloeckera apiculata, het in hoë getalle in die druiwemosmonsters oorheers en verteenwoordigende rasse het verdere aandag tydens laboratorium- en kleinskaalse wynmaakproewe geniet. 'n Protokol, waar hierdie rasse individueel gebruik is in gesamentlike geïnokuleerde fermentasies met S. cerevisiae vir die kleinskaalse produksie van wyn, is ontwikkel. 'n Verbetering in wynkwaliteit is verkry en daar is 'n verband tussen spesifieke gisspesies en druifvariëteit gevind. Gevolglik is die vermoë van C. pulcherrima om die gehalte van Chenin blanc wyn te verbeter, verder ondersoek. Resultate oor drie oesjare het gewys dat die wyn wat met die C. pulcherrima / S. cerevisiae kombinasie geproduseer is, beter was as 'n verwysingswyn (deur slegs S. cerevisiae geproduseer). Die waargenome verbetering in wynkwaliteit was egter nie aan 'n verhoging in esterinhoud te danke nie en die standaard chemiese analises het geen negatiewe afwyking uitgewys nie. Verder is gevind dat die effek van pH en wynproduksieparameters, nl. die gebruik van S02, fermentasietemperatuur en die gebruik van di-ammoniumfosfaat (DAP), dieselfde patroon as die bekend vir S. cerevisiae gevolg het. Die ontwikkelde protokol kan nou aangewend word waar verhoogde Chen in blanc wynaroma en kwaliteit verlang word.

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23

Horsch, Heidi K. "Evaluation of evolutionary engineering strategies for the generation of novel wine yeast strains with improved metabolic characteristics". Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/1537.

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24

Yip, Hopi. "Genetic manipulation of baker's yeast for improved maltose utilisation". Thesis, [Richmond, N.S.W.] : Centre for Biostructural and Biomolecular Resarch, Faculty of Science and Technolocy, University of Western Sydney, Hawkesbury, 1999. http://handle.uws.edu.au:8081/1959.7/223.

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Two yeast/E.coli shuttle vector plasmids were studied in 1994, termed pIBIDB and pBP33. According to this study, each plasmid should contain at least one ADH2UAS (upstream activation sequence in the alcohol dehydrogenase 2 gene) insert. In the present study, the constructed plasmids were analysed and transformed into laboratory strain yeast. The aim of this project was to identify the orientation, quantity and quality of the insert in the selected plasmids. Methods such as restriction analysis, polymerase chained reaction (PCR), sequencing, plate assays and enzyme assays were used to identify and evaluate the novel inserts. The data presented in this thesis suggest the inserted ADH2UAS fragment did enhance the production of maltose permease and maltase when the transformants were cultivated in maltose and ethanol-glycerol medium. The results suggested that transformants containing two inserts of ADH2UAS had a greater influence on the transformants than a single insert. But the inserts within the vectors and in transformed laboratory stain yeast appeared unstable. This could be due to the method used for plasmid construction and the storage condition of the transformants

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25

Jarnuczak, Andrew. "Mass spectrometry-based quantitative proteomics applied to the analysis of Saccharomyces cerevisiae heat stress response and chaperone deletion strains". Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/mass-spectrometrybased-quantitative-proteomics-applied-to-the-analysis-of-saccharomyces-cerevisiae-heat-stress-response-and-chaperone-deletion-strains(c653915b-70fa-44d7-9bb7-6e7965349ff0).html.

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In the last decade omics technologies enabled detailed and system-wide analysis of complex biological samples. Genomics, transcriptomics and metabolomics all benefited tremendously from technological advances in their respective fields. Proteomics was revolutionised by mass spectrometry, which allowed simultaneous identification of thousands of proteins in cells, tissues and organisms. And this mainly qualitative revolution, quickly turned quantitative. This work had two main objectives. Firstly, to apply the state of the art instrumentation, data analysis and bioinformatics methods to better our understanding of basic cell biology in a model organism Saccharomyces cerevisiae. Specifically, to quantitatively describe the effects of perturbations, such as adverse environmental conditions or chaperone gene deletions, on protein abundances in the cell. Additionally, it was aimed to demonstrate and evaluate the ability of a new timeof-flight mass spectrometer to perform large-scale absolute quantification. First, it was found that yeast cells are remarkably robust to deletions of major chaperone hub proteins (Ssa1p or Ssb1p deletions). This ability was attributed to network structure and redistribution of folding workload among other related chaperones rather than simple functional redundancy. Second, to build on the first set of results, a detailed time resolved description of yeast proteome dynamics in response to heat stress was provided for the wild type and Ssb1p chaperone mutant strains. In this study, for the first time in the literature, temporal expression patterns of many hallmark heat shock proteins were elucidated. Globally, a slow and sustained proteome remodelling or 'buffering' was revealed in both strains. However, it was also shown that the cells knocked out for the Ssb1p chaperone respond to heat in a distinctly different manner to the wild type strain. Finally, consistent and reproducible absolute quantification of multiple yeast proteomes was demonstrated using a new commercial time-of-flight mass spectrometer with ion mobility separation capabilities. The data obtained revealed global differences in cellular protein content between various chaperone prefoldin mutants as well as differential expression of a set of proteins promising to be interesting targets for further investigations.

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26

Graham, Kevin Campbell. "Production of two S. cerevisiae strains designed to enhance utilization of the yeast two-hybrid system". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/MQ32118.pdf.

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27

Chetty, Bronwyn Jean. "Improvement of cell-surface adhered cellulase activities in recombinant strains of Saccharomyces cerevisiae engineered for consolidated bioprocessing". University of Western Cape, 2021. http://hdl.handle.net/11394/8357.

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>Magister Scientiae - MSc
Consolidated bioprocessing (CBP), in which a single organism in a single reactor is responsible for the conversion of pretreated lignocellulosic biomass to bioethanol, remains an attractive option for production of commodity products if an organism fit for this process can be engineered. The yeast Saccharomyces cerevisiae requires engineered cellulolytic activity to enable its use in CBP production of second generation bioethanol. Current recombinant yeast strains engineered for this purpose must overcome the drawback of generally low secretion titres. A promising strategy for directly converting lignocellulose to ethanol is by displaying heterologous cellulolytic enzymes on the cell surface by means of the glycosylphosphatidylinositol (GPI) or similar anchoring systems. Recently, a strain producing cell-adhered enzymes in a ratio-optimized manner was created that showed significant crystalline cellulose hydrolysis.

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28

Christians, Lucinda Jo-Anne. "Proteomic characterisation of wine yeast strains for the expression of arginases involved in urea formation during fermentation". University of the Western Cape, 2018. http://hdl.handle.net/11394/6194.

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Magister Scientiae - MSc (Biotechnology)
Wine is a fermented beverage widely consumed all over the world as a recreational drink, but is known for its health benefits to humans. However, wine contain urea, a by-product of arginine hydrolysis by arginases expressed during fermentation by the wine yeast Saccharomyces cerevisiae, which reacts spontaneously with ethanol to form ethyl carbamate (EC). Ethyl carbamate was implicated in toxicity and carcinogenicity. Subsequently, small scale (18 L) Sauvignon Blanc and Cabernet Sauvignon winemaking trials using commercial wine yeasts were initialised during the 2014 and 2015 vintages to measure urea in final wines. The overall aim of this study was to investigate wine yeast protein expression during alcoholic fermentation and establish a possible correlation between urea formation by wine yeast and up/down regulated yeast proteins. Ion-exchange chromatography in conjunction with spectrophotometry was used to measure urea levels in bottled wines. The yeast strain, Prise de Mousse (PdM) was shown to be the lowest urea producer in both Sauvignon Blanc and Cabernet Sauvignon wines.

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29

AGARBATI, ALICE. "Evaluation of Microbiome, Selection and Improvement of Indigenous Yeast Strains of Typical Grape Varieties of Marche Region". Doctoral thesis, Università Politecnica delle Marche, 2019. http://hdl.handle.net/11566/263641.

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Le fermentazioni spontanee hanno suscitato grande interesse negli ultimi anni, come strategia per ottenere vini con un’elevata complessità aromatica, dovuta al pool di lieviti indigeni che intervengono nel processo fermentativo. Questi lieviti possono causare anche rallentamenti di fermentazione e produrre aromi sgradevoli; motivi per i quali l’industria enologica utilizza ceppi di lievito selezionati che garantiscano una corretta fermentazione e vini privi di difetti. Ceppi nativi di Saccharomyces cerevisiae con specifica impronta aromatica, potrebbero essere usati per produrre vini riconoscibili e che riflettano l’area di vinificazione. I lieviti nativi spesso non possiedono tutte le caratteristiche per un efficiente processo fermentativo, ma potrebbero rappresentare un punto di partenza per ottenere lieviti enologici migliorati. Nella prima parte di ricerca, la popolazione lievitiforme di uva Verdicchio e Montepulciano (biologica, convenzionale e non trattata), e la sua evoluzione durante la fermentazione spontanea è stata analizzata attraverso metodi coltura-dipendente e Next Generation Sequencing (NGS). I risultati hanno evidenziato l’influenza, della varietà di vitigno e dei trattamenti agronomici, sulla comunità lievitiforme della superficie dell’uva e del mosto che potrebbero contribuire alla fermentazione ed alle proprietà organolettiche dei vini. Inoltre, l’approccio NGS ha permesso di rilevare una maggiore biodiversità rispetto ai metodi colturali. Quest’ultimi però risultano fondamentali nel valutare la reale influenza dei lieviti sul processo fermentativo in quanto l’NGS non è in grado di distinguere i microorganismi vivi da quelli morti. Nella seconda parte del lavoro, attraverso micro-vinificazioni, sono state studiate le proprietà enologiche di due ceppi nativi di S. cerevisiae isolati da uve Verdicchio e Pecorino. I risultati hanno mostrato, per i due ceppi in studio, una cinetica fermentativa paragonabile a quella di ceppi commerciali di controllo e la capacità di conferire una complessità aromatica ceppo specifica al prodotto finale. Nella terza parte di ricerca, sfruttando la tecnica di ibridazione, sono stati ottenuti ceppi migliorati di S. cerevisiae indigeni. Lo scopo del miglioramento è stato quello di ottenere ceppi basso, o non produttori, di idrogeno solforato, anidride solforosa ed acetaldeide; caratteristiche particolarmente importanti nella produzione di vino biologico. In conclusione, è possibile agire su diversi aspetti riguardanti l’intero processo di vinificazione, che insieme contribuiscono a migliorare la qualità finale del vino e soddisfare le esigenze di mercato e dei consumatori.
In recent years, the attention of winemakers was focused on the spontaneous fermentations for the high aromatic complexity of final wines, due to the pool of indigenous yeasts involved in the fermentation process. These yeasts can also cause fermentation slowdowns and produce unpleasant aroma compounds. For these reasons winemakers uses selected yeast strains to obtain an efficient fermentation process and wines without defects. Native Saccharomyces cerevisiae strains with specific aromatic imprint could be used to produce recognizable wines that reflect the geographical area of vinification. However, these yeasts often do not have all the characteristics to led an efficient fermentation process, but they could be studied to improve their oenological traits. In the first part of the research, the fungal population of Verdicchio and Montepulciano grapes subjected to organic, conventional and not-treated farming system, and its evolution during spontaneous fermentation was analyzed through culture-dependent methods and Next Generation Sequencing (NGS). The results highlighted the influence of the vine variety and agronomic treatments on the yeasts community associated to the grape surface and the must. These yeasts probably contribute to the fermentation and the organoleptic properties of the resulting wines. Moreover, the NGS approach allowed to detect a greater biodiversity compared to cultural methods. However, the latter methods are fundamental to evaluate the real influence of yeasts on the fermentation process, since NGS is not able to distinguish live microorganisms from dead ones. In the second part of the research, through micro-vinification trials, the oenological properties of two native S. cerevisiae strains isolated from Verdicchio and Pecorino grapes were studied. The results showed that the two native strains exhibited a fermentation kinetics comparable to that of commercial control strains and the ability to confer a strain-specific aromatic complexity to the final product. In the third part of the research, using the hybridization technique, improved strains of indigenous S. cerevisiae were obtained, which possess the desired characteristics. The aim of the improvement was to obtain strains characterized by low production, or no-production, of hydrogen sulfide, sulfur dioxide and acetaldehyde; aspects particularly required in the organic wine production. In conclusion, it is possible to act on different aspects concerning the whole winemaking process, which together contribute to improve the wine quality and to satisfy the market and consumers demand.

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Volschenk, Heinrich. "Characterisation of L-malic acid metabolism in strains of Saccharomyces and the development of a commercial wine yeast strain with an efficient malo-ethanolic pathway". Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52728.

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Dissertation (PhD)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: L-Malic and tartaric acid are the most prominent organic acids in wine and playa crucial role in winemaking processes and wine quality, including the organoleptic quality and the physical, biochemical and microbial stability of wine. The production of premium wines depends on the oenologist's skill to accurately adjust wine acidity to obtain the optimum balance with other wine components to produce wine with optimum colour and flavour. Strains of Saccharomyces, in general, rarely degrade L-malic acid completely in grape must during alcoholic fermentation, with relatively minor modifications in total acidity during vinification. The degree of L-malic acid degradation, however, varies from strain to strain. Some strains of Saccharomyces are known to be able to degrade a higher percentage of L-malic acid, but the underlying reason for this phenomenon is unknown. The underlying mechanisms of this phenomenon have been partially revealed during preliminary transcriptional regulation research during this study. In contrast, S. pombe cells can effectively degrade up to 29 gil L-malic acid via the malo-ethanolic pathway that converts L-malic acid to pyruvate and CO2, and ultimately to ethanol under fermentative conditions. A number of reasons for the weak degradation of L-malic acid in Saccharomyces cerevisiae have been postulated. Firstly, S. cerevisiae lacks the machinery for the active transport of L-malic acid found in S. pombe and relies on rate-limiting simple diffusion for the uptake of extracellular L-malic acid. Secondly, the malic enzyme of S. cerevisiae has a significantly lower substrate affinity for L-malic acid (Km = 50 mM) than that of S. pombe (Km = 3.2 mM), which contributes to the weaker degradation of L-malic acid in S. cerevisiae. Lastly, the mitochondrial location of the malic enzyme of S. cerevisiae, in contrast to the cytosolic S. pombe malic enzyme, suggests that the S. cerevisiae malic enzyme is inherently subject to the regulatory effects of fermentative metabolism. The malate permease gene tmael) and the malic enzyme gene (mae2) of S. pombe was therefore cloned and co-expressed in single or multi-copy under regulation of the constitutive S. cerevisiae 3-phosphoglycerate kinase (PGK1) promoter and terminator sequences in a laboratory strain of S. cerevisiae. This introduced a strong malo-ethanolic phenotype in S. cerevisiae where L-malic acid was rapidly and efficiently degraded in synthetic and Chardonnay grape must with the concurrent production of higher levels of ethanol. Functional expression of the malo-ethanolic pathway genes of S. pombe in a laboratory strain of S. cerevisiae paved the way for the genetic modification of industrial wine yeast strains of Saccharomyces for commercial winemaking. A prerequisite for becoming an inherited component of yeast is the stable integration of the malo-ethanolic genes into the genome of industrial wine yeast strains. Genetic engineering of wine yeasts strains of Saccharomyces is, however, complicated by the homothallic, multiple ploidy and prototrophic nature of industrial strains of Saccharomyces. Transformation and integration of heterologous genes into industrial strains of Saccharomyces require the use of dominant selectable markers, i.e. antibiotic or toxic compound resistance markers. Integration of these markers into the yeast genome is, however, not acceptable for commercial application due to the absence of long-term risk assessment and consumer resistance. A unique strategy for the integration of the S. pombe mae} and mae2 expression cassettes without the incorporation of any non-yeast derived DNA sequences was. The malo-ethanolic cassette, containing the S. cerevisiae PGK} promoter and terminator regions together with the S. pombe mae] and mae2 open reading frames, was integrated into the VRA3 locus of an industrial strain of Saccharomyces bayanus EC 1118 during co-transformation with a phleomycin-resistance plasmid, pUT332. After initial screening for phleomycin resistance, S. bayanus EC1118 transformants were cured of the phleomycin-resistance plasmid, resulting in the loss of non-yeast derived DNA sequences. After correct integration of the mae] and mae2 expression cassettes was verified, small-scale vinification in synthetic and Chardonnay grape must with stable transformants resulted in rapid and complete degradation of L-malic acid during the early stages of alcoholic fermentation. Integration and expression of the malo-ethanolic genes in S. bayanus ECll18 had no adverse effect on the fermentation ability of the yeast, while sensory evaluation and chemical analysis of the Chardonnay wines indicated an improvement in wine flavour compared to the control wines, without the production of any off-flavours.
AFRIKAANSE OPSOMMING: L-Appelsuur en wynsteensuur is die mees prominente organiese sure in wyn en speel 'n kritiese rol in die wynbereidingsproses en organoleptiese wynkwaliteit, insluitende die fisiese, biochemiese en mikrobiese stabiliteit van wyn. Die produksie van hoë-kwaliteit wyne berus op die vermoë van 'n wynmaker om die suurinhoud korrek aan te pas om sodoende 'n gebalanseerde produk met optimale geur en kleur te produseer. Saccharomyces rasse kan gewoonlik nie appelsuur volledig tydens alkoholiese gisting benut nie en dra dus nie noemenswaardig tot 'n verlaging van die totale suurinhoud van wyn by nie. Die mate van appelsuur afbraak deur Saccharomyces wissel egter van ras tot ras. Sekere Saccharomyces rasse kan 'n groter persentasie appelsuur afbreek, maar die onderliggende rede vir hierdie verskynsel is onbekend. Die onderliggende meganismes vir hierdie verskynsel is gedurende hierdie studie uitgelig na afloop van voorlopige transkripsionele regulerings studies op die malaatensiemgeen. In teenstelling hiermee kan S. pombe tot 29 gIl appelsuur via die malo-alkoholiese padweg afbreek waartydens appelsuur na pirodruiwesuur en CO2, en uiteindelik na alkoholonder fermentatiewe toestande omgeskakel word. Verskeie redes vir die swak afbraak van appelsuur deur Saccharomyces cerevisiae is voorgestel. Eerstens beskik S. cerevisiae nie oor 'n meganisme vir die aktiewe transport van appelsuur, soos in die geval van S. pombe nie, en is aangewese op die stadige opname van appelsuur deur eenvoudige diffusie. Tweedens het die S. cerevisiae malaatensiem 'n baie laer substraataffiniteit vir appelsuur (Km = 50 mM) in vergelyking met die van S. pombe (Km = 3.2 mM), wat verder bydra tot die swak afbraak van appelsuur in S. cerevisiae. Laastens dra die mitochondriale ligging van die S. cerevisiae malaatensiem in teenstelling met die sitoplasmiese ligging van die S. pombe malaatensiem, verder by tot die swak afbraak van appelsuur, aangesien die mitochondria onder fermentatiewe toestande negatief gereguleer word. Die malaatpermease geen (maely en malaatensiem geen (mae2) van S. pombe is gevolglik gekloneer en heteroloog in 'n laboratoriumras van S. cerevisiae onder die beheer van die konstitutiewe 3-fosfogliseraat kinase (PGKI) promoter- en termineerdervolgordes uitgedruk. 'n Sterk malo-alkoholiese fenotipe was duidelik tydens fermentasies met die rekombinante gis in sintetiese en Chardonnay druiwemos, met 'n gepaardgaande verhoging in alkoholvlakke. Funksionele uitdrukking van die malo-alkoholiese gene van S. pombe in 'n S. cerevisiae laboratoriumras het die weg vir die genetiese modifisering van industriële wynrasse van S. cerevisiae vir kommersiële wynfermentasie gebaan. Om 'n integrale deel van die gis te word, moet die malo-alkoholiese gene stabiel in die genoom van industriële wynrasse geïntegreer word. Genetiese manipulering van industriële wynrasse word egter bemoeilik deur die homotalliese, multi-ploïediese en prototrofiese aard van industriële Saccharomyces rasse. Transformasie en integrasie van heteroloë gene in industriële Saccharomyces rasse vereis die gebruik van dominante merkers, bv. weerstandbiedendheid teen antibiotika of ander gifstowwe. Integrasie van hierdie merkers in die gisgenoom is egter nie vir kommersiële toepassing aanvaarbaar nie weens die afwesigheid van langtermyn risikobepalings en verbruikersweerstand. Tydens hierdie studie is daar dus gepoog om industriële wynrasse met 'n unieke strategie geneties te verbeter sodat slegs gis-DNA tydens die integrasie van die S. pombe mae1 en mae2 uitdrukkingskassette in die gisgenoom opgeneem word. Die Malo-alkoholiese integrasiekasset wat slegs die S. pombe mae1, mae2 oopleesrame en die S. cerevisiae PGK1 promoter en termineerdervolgordes bevat, is in die URA3 lokus van Saccharomyces bayanus ECll18 geïntegreer tydens parallelle transformasie met 'n 'phleomycin' weerstandbiedendheidsplasmied. Na seleksie van transformante op 'phleomycin' -bevattende media, is die S. bayanus EC 1118 transformante in nieselektiewe kondisies opgegroei sodat verlies van die 'phleomycin' plasmied kon plaasvind. Integrasie van die mae1 en mae2 uitdrukkingskassette is bevestig en kleinskaalse fermentasies in sintetiese en druiwemos het 'n vinnige en doeltreffende afbraak van appelsuur in die vroeë fases van die alkoholiese fermentasie getoon. Integrasie en uitdrukking van die malo-alkoholiese gene in S. bayanus ECl118 het geen nadelige effek op die fermentasievermoë van die gis getoon nie, terwyl sensoriese en chemiese ontleding van die Chardonnay wyne 'n verbetering in aroma relatief tot die kontrole wyne getoon het, met die afwesigheid van enige afgeure.

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Dahabieh, Matthew Solomon. "Metabolic engineering of industrial yeast strains to minimize the production of ethyl carbamate in grape and Sake wine". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/790.

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During alcoholic fermentation Saccharomyces cerevisiae metabolizes L-arginine to ornithine and urea. S. cerevisiae can metabolize urea through the action of urea amidolyase, encoded by the DUR1,2 gene; however, DUR1,2 is subject to nitrogen catabolite repression (NCR) in the presence of high quality nitrogen sources during fermentation. Being cytotoxic at high concentrations, urea is exported into wine where it spontaneously reacts with ethanol, and forms the carcinogen ethyl carbamate (EC). Urea degrading yeast strains were created by integrating a linear cassette containing the DUR1,2 gene under the control of the S. cerevisiae PGK1 promoter and terminator signals into the URA3 locus of the Sake yeast strains K7 and K9. The ‘self-cloned’ strains K7EC- and K9EC- produced Sake wine with 68% less EC. The Sake strains K7EC- and K9EC- did not efficiently reduce EC in Chardonnay wine due to the evolutionary adaptation of said strains to the unique nutrients of rice mash; therefore, the functionality of engineered yeasts must be tested in their niche environments as to correctly characterize new strains. S. cerevisiae possesses an NCR controlled high affinity urea permease (DUR3). Urea importing yeast strains were created by integrating a linear cassette containing the DUR3 gene under the control of the PGK1 promoter and terminator signals into the TRP1 locus of the yeast strains K7 (Sake) and 522 (wine). In Chardonnay wine, the urea importing strains K7D3 and 522D3 reduced EC by 7% and 81%, respectively; reduction by these strains was equal to reduction by the urea degrading strains K7EC- and 522EC-. In Sake wine, the urea degrading strains K7EC- and 522EC- reduced EC by 87% and 84% respectively, while the urea importing strains K7D3 and 522D3 were significantly less capable of reducing EC (15% and 12% respectively). In Chardonnay and Sake wine, engineered strains that constitutively co-expressed DUR1,2 and DUR3 did not reduce EC more effectively than strains in which either gene was expressed solely. Uptake of 14C-urea under non-inducing conditions was enhanced in urea importing strains; parental strains failed to incorporate any 14C-urea thus confirming the functionality of the urea permease derived from the integrated DUR3 cassette.

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Mubazangi, Munyaradzi. "Optimization of the conversion of lignocellulosic agricultural by-products to bioethanol using different enzyme cocktails and recombinant yeast strains". Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/6891.

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Thesis (MSc)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: The need to mitigate the twin crises of peak oil and climate change has driven a headlong rush to biofuels. This study was aimed at the development of a process to efficiently convert steam explosion pretreated (STEX) sugarcane bagasse into ethanol by using combinations of commercial enzyme cocktails and recombinant Saccharomyces cerevisiae strains. Though enzymatic saccharification is promising in obtaining sugars from lignocellulosics, the low enzymatic accessibility of the cellulose and hemicellulose is a key impediment thus necessitating development of an effective pretreatment scheme and optimized enzyme mixtures with essential accessory activities. In this context, the effect of uncatalysed and SO2 catalysed STEX pretreatment of sugarcane bagasse on the composition of pretreated material, digestibility of the water insoluble solids (WIS) fraction and overall sugar recovery was investigated. STEX pretreatment with water impregnation was found to result in a higher glucose recovery (28.1 g/ 100 bagasse) and produced WIS with a higher enzymatic digestibility, thus was used in the optimization of saccharification and fermentation. Response surface methodology (RSM) based on the 33 factorial design was used to optimize the composition of the saccharolytic enzyme mixture so as to maximize glucose and xylose production from steam exploded bagasse. It was established that a combination of 20 FPU cellulase/ g WIS and 30 IU -glucosidases/ g WIS produced the highest desirability for glucose yield. Subsequently the optimal enzyme mixture was used to supplement enzyme activities of recombinant yeast strains co-expressing several cellulases and xylanases in simultaneous saccharification and fermentations SSFs. In the SSFs, ethanol yield was found to be inversely proportional to substrate concentration with the lowest ethanol yield of 70% being achieved in the SSF at a WIS concentration of 10% (w/v). The ultimate process would however be a one-step “consolidated” bio-processing (CBP) of lignocellulose to ethanol, where hydrolysis and fermentation of polysaccharides would be mediated by a single microorganism or microbial consortium without added saccharolytic enzymes. The cellulolytic yeast strains were able to autonomously multiply on sugarcane bagasse and concomitantly produce ethanol, though at very low titres (0.4 g/L). This study therefore confirms that saccharolytic enzymes exhibit synergism and that bagasse is a potential substrate for bioethanol production. Furthermore the concept of CBP was proven to be feasible.
AFRIKAANSE OPSOMMING: Die behoefte om die twee krisisse van piek-olie en klimaatsverandering te versag, het veroorsaak dat mense na biobrandstof as alternatiewe energiebron begin kyk het. Hierdie studie is gemik op die ontwikkeling van 'n proses om stoomontplofde voorafbehandelde (STEX) suikerriet bagasse doeltreffend te omskep in etanol deur die gebruik van kombinasies van kommersiële ensiem mengsels en rekombinante Saccharomyces cerevisiae stamme. Alhoewel ensiematiese versuikering belowend is vir die verkryging van suikers vanaf lignosellulose, skep die lae ensiematiese toeganklikheid van die sellulose en hemisellulose 'n hindernis en dus is die ontwikkeling van' n effektiewe behandelingskema en optimiseerde ensiemmengsels met essensiële bykomstige aktiwiteite noodsaaklik. In hierdie konteks, was die effek van ongekataliseerde en SO2 gekataliseerde stoomontploffing voorafbehandeling van suikerriet bagasse op die samestelling van voorafbehandelde materiaal, die verteerbaarheid van die (WIS) breuk van onoplosbare vastestowwe in water (WIS), en die algehele suikerherstel ondersoek. Daar was bevind dat stoomontploffing behandeling (STEX) met water versadiging lei tot 'n hoër suikerherstel (21.8 g/ 100g bagasse) en dit het WIS met ‘n hoër ensimatiese verteerbaarheid vervaardig en was dus gebruik in die optimalisering van versuikering en fermentasie. Reaksie oppervlak metodologie (RSM), gebasseer op die 33 faktoriële ontwerp, was gebruik om die samestelling van die ‘saccharolytic’ ensiemmengsel te optimaliseer om sodoende die maksimering van glukose en ‘xylose’ produksie van stoomontplofde bagasse te optimaliseer. Daar was bevestig dat ‘n kombinasie van 20 FPU sellulase/ g WIS en 30 IU ‘ -glucosidases/ g’ WIS die hoogste wenslikheid vir glukose-opbrengs produseer het. Daarna was die optimale ensiemmengsel gebruik om ensiemaktiwiteit van rekombinante gisstamme aan te vul, wat gelei het tot die medeuitdrukking van verskillende ‘cellulases’ en ‘xylanases’ in gelyktydige versuikering en fermentasie SSFs. In die SSFs was daar bevind dat die etanol-produksie omgekeerd proporsioneel is tot substraat konsentrasie, met die laagste etanolopbrengs van 70% wat bereik was in die SSF by ‘n WIS konsentrasie van 10% (w/v). Die uiteindelike proses sal egter 'n eenmalige "gekonsolideerde" bioprosessering (CBP) van lignosellulose na etanol behels, waar die hidrolise en fermentasie van polisakkariede deur' n enkele mikroorganisme of mikrobiese konsortium sonder bygevoegde ‘saccharolytic’ ensieme bemiddel sal word. Die ‘cellulolytic’ gisstamme was in staat om vanself te vermeerder op suikerriet bagasse en gelyktydig alkohol te produseer, al was dit by baie lae titres (0.4 g/L). Hierdie studie bevestig dus dat ‘saccharolytic’ ensieme sinergisme vertoon en dat bagasse 'n potensiële substraat is vir bio-etanol produksie. Daar was ook onder meer bewys dat die konsep van CBP uitvoerbaar is.
The National Research Foundation (NRF) for financial support

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33

Von, Mollendorff Anke. "The impact of wine yeast strains on the aromatic profiles of Sauvignon blanc wines derived from characterized viticultural treatments". Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80181.

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Thesis (MScAgric)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Grape must is a complex medium, and during wine production numerous biochemical pathways and metabolic reactions are taking place simultaneously to produce a specific taste and aroma. Microorganisms, specifically yeast, play a key role in the formation of metabolites formed during alcoholic fermentation. Sauvignon blanc, a well studied grape cultivar, is known to have a versatile range of aroma profiles ranging from “green” to “tropical”. It has been broadly stated that a “green” Sauvignon blanc can be created in the vineyard and a “tropical” Sauvignon blanc can be created by selecting a specific yeast strain, and that the balance between “green” and “tropical” characters is essential for the final aroma profile. Except for grape-derived varietal aromatic compounds such as methoxypyrazines (green), volatile thiols (tropical) and monoterpenes (floral), yeast derived volatile compounds including esters, higher alcohols, fatty acids and carbonyl compounds will also contribute to the final wine aroma. The main aim of this study was to assess how viticultural treatment-derived differences in grape must, can impact on aroma production when this grape must is fermented with different commercial wine yeast strains. The viticulture treatment focused on light intensity modulated through canopy treatment. Volatile aroma differences were compared for canopy and yeast treatments, specifically focusing on the fermentation derived bouquet (esters, higher alcohols, volatile fatty acids, carbonyl compounds and monoterpenes). Results showed significant differences between initial must compositions, including titratable acidity, malic acid and yeast assimilable nitrogen. The volatile aroma compounds were also significantly impacted although no noticeable effect on the overall fermentation kinetics was observed. Depending on the yeast strain differences in volatile compounds varied. A clear vintage effect is noticeable between volatile compounds affected by the treatments. Data generated in 2012 shows clear differences between ethyl- and acetate esters and could clearly be grouped according to yeast strain through multivariate analysis. Sensory evaluation results could clearly be distinguished according to canopy treatment and to a lesser degree according to yeast strain used. This indicates that although yeast has a more prominent impact on the fermentative bouquet that develops during alcoholic fermentation the overriding aroma is primarily derived from grape-derived metabolites which can be manipulated by canopy treatments. None the less the difference in fermentation bouquet does add to the complexity of the wine especially in the case of fermentation derived “tropical” aromas including guava and passion fruit. In some cases where shaded grapes had higher ester concentrations, the resultant wine also had higher aroma quality. This study has contributed to a better understanding of the complex relationships between canopy manipulation and yeast selection on aroma formation. The analysis of volatile aroma alone however is not enough to understand the final perception of wine taste and further indepth studies of the viticultural and oenological factors is needed. In particular, this project has focused on a single vineyard over only two vintages. The general validity of the conclusions derived from this study therefore will require additional data sets.
AFRIKAANSE OPSOMMING: Druiwemos is ‘n komplekse medium en tydens wynbereiding is daar verskeie biochemiese weë en metaboliese reaksies wat gelyktydig plaasvind om ‘n spesifieke smaak en aroma te produseer. Mikro-organismes, veral gis, speel ‘n sleutelrol in die vorming van metaboliete tydens alkoholiese gisting. Sauvignon blanc, ‘n goed bestudeerde druifkultivar, besit ‘n veelsydige reeks aromaprofiele wat wissel van “groen” tot “tropies”. Oor die algemeen word dit voorgehou dat ‘n “groen” Sauvignon blanc in die wingerd geskep word, terwyl ‘n “tropiese” Sauvignon blanc geskep kan word deur ‘n spesifieke gisras te selekteer, en die balans tussen “groen” en “tropiese” karakters is noodsaaklik vir die finale aromaprofiel. Behalwe vir druifafgeleide kultivarafhanklike aromatiese verbindings soos metoksipirasiene (groen), vlugtige tiole (tropies) en monoterpene (blomagtig), sal gisafgeleide vlugtige komponente, waaronder esters, hoër alkohole, vetsure en karbonielverbindings, ook tot die finale wynaroma bydra. Die hoofdoelwit van hierdie studie was om te bepaal hoe verskille in druiwemos wat afkomstig is van wynkundige behandeling ‘n impak op aromaproduksie kan hê wanneer hierdie druiwemos met verskillende kommersiële wyngisrasse gegis word. Die wynkundige behandeling het gefokus op ligintensiteit wat deur lowerbehandeling gereguleer is. Vlugtige aromaverskille is op grond van lower- en gisbehandelings vergelyk, met ‘n spesifieke fokus op die gistingsafgeleide boeket (esters, hoër alkohole, vlugtige vetsure, karbonielverbindings en monoterpene). Die resultate het beduidende verskille getoon tussen aanvanklike mossamestellings, waaronder titreerbare suurheid, appelsuur en gis-assimileerbare stikstof. Daar was ook ‘n noemenswaardige impak op die vlugtige aromaverbindings, hoewel geen merkbare effek op die algehele gistingskinetika waargeneem kon word nie. Die verskille in vlugtige verbindings het gewissel op grond van die gisras. ‘n Duidelike oesjaareffek was merkbaar tussen vlugtige verbindings wat deur die behandelings geaffekteer is. Data wat in 2012 gegenereer is, toon duidelike verskille tussen etiel- en asetaatesters en kon duidelik m.b.v. meervariantanalise volgens gisras gegroepeer word. Die resultate van die sensoriese evaluering kon duidelik volgens lowerbehandeling onderskei word, en tot ‘n mindere mate volgens die gisras wat gebruik is. Dít dui daarop dat hoewel gis ‘n meer prominente impak het op die gistingsboeket wat tydens alkoholiese gisting ontwikkel, is die oorheersende aroma hoofsaaklik afgelei van druifafgeleide metaboliete wat deur lowerbehandelings gemanipuleer kan word. Nietemin dra die verskil in gistingsboeket by tot die kompleksiteit van die wyn, veral in die geval van gistingsafgeleide “tropiese” aromas, insluitend koejawel en grenadella. In sommige gevalle waar beskadude druiwe hoër esterkonsentrasies gehad het, het die gevolglike wyn ook ‘n hoër aromakwaliteit gehad. Hierdie studie dra by tot ‘n beter begrip van die effek van die komplekse verhoudings tussen lowermanipulasie en gisseleksie op aromavorming. ‘n Analise van vlugtige aroma alleen is egter nie voldoende om die finale persepsie van wynsmaak te begryp nie en bykomende diepgaande studies van die wingerdkundige en wynkundige faktore word benodig. Hierdie projek het in die besonder gefokus op ‘n enkele wingerd oor slegs twee oesjare. Die algemene geldigheid van die afleidings wat van hierdie studie gemaak word, sal dus bykomende datastelle vereis.
The National Research Foundation and Postgraduate Merit Bursary for financial support

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Groß, Annett [Verfasser], Gerhard [Akademischer Betreuer] [Gutachter] Rödel e Günter [Gutachter] Vollmer. "Genetically Tailored Yeast Strains for Cell-based Biosensors in White Biotechnology / Annett Groß ; Gutachter: Gerhard Rödel, Günter Vollmer ; Betreuer: Gerhard Rödel". Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1126921866/34.

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Groß, Annett [Verfasser], Gerhard [Akademischer Betreuer] Rödel e Günter [Gutachter] Vollmer. "Genetically Tailored Yeast Strains for Cell-based Biosensors in White Biotechnology / Annett Groß ; Gutachter: Gerhard Rödel, Günter Vollmer ; Betreuer: Gerhard Rödel". Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1126921866/34.

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Coi, Anna Lisa. "A genome based approach to characterize genes involved in yeast adaptation to Sherry-like wines’ biological ageing". Thesis, Montpellier, SupAgro, 2014. http://www.theses.fr/2014NSAM0005/document.

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La fermentation œnologique et le vieillissement oxydatif des vins sous voile représentent des modes de vie très contrastés qui sont effectués par deux lignées différentes de souches de levures de l'espèce Saccharomyces cerevisiae. Dans cette thèse, nous avons comparé le génome de souches de levures de voile à celui de levures de vin afin de détecter leurs spécificités. Nous tout d'abord sélectionné 16 souches (8 levures de vin et 8 levures de voile) isolées en France, Hongrie, Italie et Espagne, pour séquencer leur génome sur une plateforme Illumina (HiSeq2000). Nous avons également développé un ensemble de souches de vin et de voile haploïdes pour l'évaluation moléculaire de différentes cibles. Nous avons également mis au point un milieu synthétique mimant le vin à cette fin. A partir de la comparaison des séquences du génome nous avons établi une phylogénie qui montre que les levures de voile représentent un groupe spécifique de levure, différentes des levures de vin, puis à partir de différentes méthodes (analyse en composantes principale, diversité nucléotidique et D de Tajima) nous avons identifié des régions divergentes. Ces régions variantes comprennent des gènes remplissant plusieurs fonctions clé associées à la croissance en voile. En particulier, des variations alléliques ont été rencontrées chez les levures de voile pour plusieurs gènes impliqués dans la régulation de l'expression de FLO11 tels que les voies MAP kinase, ou des voies Ras/cAMP/PKA, ainsi que pour plusieurs gènes impliqués dans l'homéostasie des cations divalents de métaux de transition tels que le zinc, le cuivre ou le fer. La comparaison des transcriptomes d'une levure de voile et d'une levure de vin sur notre milieu synthétique a révélé des différences d'expression pour les floculines (FLO1, 5, 8, 11) ainsi que pour le transport des hexoses, mais a également suggéré que la levure de voile P3-D5 était en situation de carence en zinc et en inositol par rapport à la levure de vin, tandis que la levure de vin K1 exprimait certains gènes suggérant des défauts mitochondriaux. L'impact de la variation allélique de plusieurs gènes a été évalué dans le phénotype de voile: le transporteur de zinc à haute affinité Zrt1 ainsi que la pyruvate décarboxylase majeure Pdc1
Wine fermentation and flor ageing are performed by two groups of the yeast Saccharomyces cerevisiae, with very different lifestyles. In this thesis we have studied the genome of flor yeast in comparison to wine yeast in order to unravel their specificities. We have first selected 16 strains (8 wine and 8 flor) from France, Hungary, Italy and Spain in order to sequence their genome sequence on an Illumina HiSeq2000 platform. Three flor strains and two wine strains were haploidized in order to obtain a set of haploid flor strains for the molecular evaluation of different targets. We developed as well a synthetic media mimicking wine for that purpose. From the genome sequence we have drawn a phylogeny that showed that flor yeasts represent a specific lineage of yeast, different from the wine strains lineage, and identified divergent regions. These regions contain genes involved in key functions and several associated with velum growth. Remarkably, many genes involved in FLO11 regulation such as MAP kinase, or Ras/PKA pathways were mutated among flor strains and many variations were encountered in genes involved in metal homeostasis such as zinc and divalent metal transporters. A transcriptome analysis comparing one flor and one wine yeast on our wine synthetic media revealed expression differences associated to floculins and hexose transport, but also suggested that flor yeast P3-D5 face a zinc and inositol deficiency, whereas wine yeast K1 presented mitochondrial defects. The impact of allelic variation of several genes coding for the high affinity zinc transporter (ZRT1), and the major pyruvate decarboxylase (PDC1) has been evaluated in order to assess their role in the flor phenotype

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Meier-Dörnberg, Tim [Verfasser], Friedrich [Akademischer Betreuer] Jacob, Dirk [Gutachter] Weuster-Botz, Friedrich [Gutachter] Jacob e Rudi F. [Gutachter] Vogel. "Comparative characterization of selected Saccharomyces yeast strains as beer fermentation starter cultures / Tim Meier-Dörnberg ; Gutachter: Dirk Weuster-Botz, Friedrich Jacob, Rudi F. Vogel ; Betreuer: Friedrich Jacob". München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1175091790/34.

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Kulkarni, Priyanka Prashant. "Use of non Saccharomyces yeast strains coupled with ultrasound treatments as a novel technique to accelerate aging over lees of red wines and its repercussion in sensorial parameters". Master's thesis, ISA/UL, 2014. http://hdl.handle.net/10400.5/8636.

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Mestrado Vinifera EuroMaster - Instituto Superior de Agronomia
Ageing over lees has long been considered to benefit the overall quality of wine, enhancing the body and mouthful as well as sensorial complexity, color stability. Despite of all the positive attributes conferred by this technique, it is a complex process which could last up to years and is affected by several variables of different nature and complexities. This process has several economic impacts representing large investments for all producers to store the wines in cellars as well as the wine maker has to bear the potential risk associated with the organoleptic and microbiological alterations in the wines. Thus, it is important for the winemakers to optimize the time of ageing on lees. Further more in today’s fiercely competitive market it is reasonable to develop new strategies and techniques to accelerate the ageing over lees process, shorten the storage time and achieve better quality. In this study two novel techniques: use of non Saccharomyces strains coupled with ultrasound treatment were tested to see their efficiency for accelerating aging over lees. The combined effects of the techniques were tested to see their impacts on the polysaccharide release and on the organoleptic properties of red wine. Release of polysaccharides was analyzed by HPLC-RI. Anthocyanins and aroma compounds were analyzed by using HPLC-PDAD/ESI-MS, GC-FID respectively. Also Color and Total Phenolic Index were recorded periodically along the experiment. Results showed that ultrasound treatment is a reliable technique for shortening the ageing on lees process by strongly increasing the concentration of polysaccharides released into the wine after only two weeks treatment and without adversely affecting the sensorial quality of the wine. Additions of sand as an abrasives agent increased the polysaccharide release. Furthermore the non Saccharomyces strains of Schizosaccharomyces pombe, Saccharomyces ludwigii and Brettanomyces showed better results with regards to the amount of polysaccharide release compared to the control Saccharomyces strains. Interesting results with Brettanomyces were observed, as the use of this particular strain did not impart any off flavors to the wine. This can be explained by the use of lyophilized strains used in this study which were dosed in the wine to carry out the aging over lees. Ultrasonic treatment coupled with aging over lees resulted in reduction of anthocyanin content of the wine and also effected the aroma compounds.In conclusion this study illustrated the use of Ultrasounds and Non Saccharomyces strains as novel techniques for aging over lees, however more research in this field is required to study the clear effects on ultrasounds on the chemical composition of wine before replicating the application on a large scale production

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Mogotsi, Lerato Bonolo. "An assessment of the lipopolysaccharide toxicity of rough and smooth escherichia coli strains cultivated in the presence of zygosaccharomyces bailli". Thesis, Bloemfontein : Central University of Technology, Free State, 2011. http://hdl.handle.net/11462/151.

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Thesis (M. Tech. Environmental health) -- Central University of technology, Free State, 2011
In nature microorganisms do not exist alone, but in association with one another. These kinds of associations can also be found in food industries, where cells of the same or different species can attach to pipes (biofilm formation) and a variety of surfaces in food processing environments and in food product such as yoghurt which can contain both yeast and bacteria originating from the starter culture as well as fruit. To control food spoilage organisms and food-borne pathogens preventative measures such as good manufacturing processes, the use of sanitizers and preservatives as well as hazard analysis critical control points (HACCP) are crucial in food industries. Sanitation of the working surface, floors, pipes, containers and equipment is a stepwise application of a detergent, acid or alkali rinse, a disinfectant treatment followed by final rinsing. If rinsing of the sanitizer is not done properly it may end up in the product in sub-lethal doses. In this study the influence of Liquid Hypochlorite (LH) and Liquid Iodophore (LI) sanitizers on organism growth and toxicity was evaluated. The organisms investigated included Escherichia coli 0113, Escherichia coli 026 and Zygosaccharomyces bailii Y-1535 in yeast malt broth, which was supplemented with LH and LI at sub-lethal concentrations 0.05% LH, 0.2% LH and 0.075% LI. Subsequently, bacterial and yeast growth responses as pure cultures and in combination (E. coli + Z. bailii) were measured as colony forming units and optical density values. Incorporation of the sanitizers in the growth media resulted in different levels of growth inhibition. Z. bailii proved more robust and the growth rate was not influence significantly by the addition of sanitizers or communal growth with either E. coli strains. The growth rate of both E. coli strains decreased where grown in combination with Z. bailii as well as in the presence of sanitizers, with the most influence exerted by LH. Changes in endotoxicity following the growth of the test samples (stressed cells) and the control (unstressed) were measured by the limulus amoebocyte lysate (LAL) and porcine IL-6 ELISA methods. Where E. coli strains were cultured together with Z. bailii the toxicity of tire mixture showed a decrease over time when measured with the limulus amoebocyte assay method. Interestingly the communal growth of the E. coli strains and Z bailii produced different toxicity profiles when the IL-6 porcine method was used, hi both cases, where E. coli strains were cultured together with Z. bailii the toxicity of the mixture showed an increase over tune when measured by this assay. Other than a similar toxicity profile for E. coli 0113 grown in pure culture, the comparison between results obtained using the LAL or porcine IL-6 methods yielded no correlation in determined toxicity. It was established that LH and LI sanitizers as well as communal growth had an influence in the toxicity of LPS/EPS and the method used to determine such toxicity should be carefully considered.

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Vogelmann, Stephanie Anke [Verfasser], e Christian [Akademischer Betreuer] Hertel. "Impact of process parameters on the sourdough microbiota, selection of suitable starter strains, and description of the novel yeast Cryptococcus thermophilus sp. nov. / Stephanie Anke Vogelmann. Betreuer: Christian Hertel". Hohenheim : Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim, 2013. http://d-nb.info/1044975032/34.

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Vogelmann, Stephanie [Verfasser], e Christian [Akademischer Betreuer] Hertel. "Impact of process parameters on the sourdough microbiota, selection of suitable starter strains, and description of the novel yeast Cryptococcus thermophilus sp. nov. / Stephanie Anke Vogelmann. Betreuer: Christian Hertel". Hohenheim : Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:100-opus-8888.

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Schiavone, Marion. "Combination of biochemical, molecular and biophysical approaches to investigate the impact of strain background and production process on the yeast cell wall composition and molecular architecture". Thesis, Toulouse, INSA, 2014. http://www.theses.fr/2014ISAT0043.

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L’intérêt pour la paroi de la levure s’est accru récemment par l’explosion des activités de bioraffineries augmentant la production de biomasse, et par le besoin de valoriser cette biomasse dans d’autres débouchés comme en nutrition animale et en œnologie pour leurs propriétés probiotiques et de sorption. Le but de cette thèse était de combiner des approches biochimiques, biophysiques et les puces à ADN afin d'étudier les relations entre ces paramètres ainsi que de mettre en évidence l'impact des souches, des conditions de croissance et des procédés sur la composition et les propriétés biophysiques de la paroi cellulaire. Une méthode acido-enzymatique a été développée pour quantifier spécifiquement chacun des quatre composants de la paroi cellulaire de la levure, à savoir les mannanes, la chitine, les β-1,3-glucanes et les β-1,6-glucanes. Cette méthode a été validée sur des souches mutantes et a permis d’évaluer les effets de divers stress. Ultérieurement, l'utilisation de la microscopie à force atomique (AFM) a permis l'étude des mêmes souches et de quatre souches utilisées dans la fermentation industrielle. Ils ont démontré des propriétés nanomécaniques et adhésives distinctes, en raison de différences dans la composition et la structure de la paroi cellulaire. Dans la dernière partie, les effets du procédé d’autolyse et du séchage à lit fluidisé sont présentés. Ce procédé industriel ne modifie pas la composition de la paroi cellulaire, mais induit une modification de la topographie et des propriétés de surface de la cellule. En outre, en utilisant l'AFM nous avons imagés sur S. cerevisiae des patchs hautement adhésifs formant des nanodomaines à la surface de la cellule
Due to increasing yeast biomass production resulting from the expansion of the Biorefinery as an alternative to petrol-based energy, the yeast cell wall is receiving an increasing interest as an added value product targeting agro-nutrition markets, such as in animal nutrition and in wine for its probiotic and sorption properties. The purpose of this thesis was therefore to combine DNA microarrays, biochemical and biophysical approaches in order to investigate the relationships between these parameters as well as to highlight the impact of strains, growth conditions and processes on the cell wall composition and biophysical properties. To achieve this objective, an acido-enzymatic method was developed to specifically quantify each of the four components of the yeast cell wall, namely mannan, chitin, β-1,3-glucan and β-1,6-glucan. This method was validated on mutant strains and allowed highlighten various stresses effects. Then, the use of atomic force microscopy (AFM) has allowed investigating the same strains and four strains used in industrial fermentation. They demonstrated distinct nanomechanical and adhesive properties, due to differences in their cell wall structure and composition. In the last part, the effects of the autolysis and fluid-bed drying processes are presented. This industrial process does not change the composition of the cell wall but induces a modification in topography and surface properties of the cell. Moreover, using AFM we imaged on S. cerevisiae cell surface highly adhesive patches forming nanodomains

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Toyama, Brandon Hiroyuki. "The structural basis of yeast prion strain variants". Diss., Search in ProQuest Dissertations & Theses. UC Only, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3378511.

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Daubenspeck, Robert Louis. "Construction and analysis of a starch-degrading strain of distillers' yeast". Thesis, Heriot-Watt University, 1994. http://hdl.handle.net/10399/1414.

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De, Klerk Daniel. "Co-expression of aroma liberating enzymes in a wine yeast strain". Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1888.

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Thesis (Msc (Viticulture and Oenology. Institute for Wine Biotechnology))--University of Stellenbosch, 2009.
Monoterpenes are important aroma compounds in certain grape varieties such as Muscat, Gewürztraminer and Riesling and are present as either odourless, glycosidically bound complexes or as free aromatic monoterpenes. These complexes occur as monoglucosides or, when present as diglycosides, most commonly as 6-O-α-L-arabinofuranosyl-β-D-glucopyranosides of mainly linalool, geraniol, nerol and citronellol. The release of monoterpenes from non-volatile glycosidically bound precursors occurs either by acid hydrolysis or enzymatic hydrolysis. High temperature acid hydrolysis causes a rearrangement of the monoterpene aglycones and a decrease in the aroma and changes in the aromatic characteristics of monoterpenes and is therefore not suitable. Enzymatic hydrolysis does not modify the monoterpene aglycones and can be an efficent method to release potentially volatile monoterpenes. α-L-arabinofuranosidase and β-glucosidase are important enzymes responsible for the liberation of monoterpene alcohols from their glycosides. Glycosidases from Vitis vinifera and Saccharomyces cerevisiae are severely inhibited by winemaking conditions and this leads to unutilized aroma potential, while commercial preparations of aroma liberating enzymes are crude extracts that often have unwanted and unpredictable side effects. It is therefore of interest to investigate alternative measures to release glycosidically bound monoterpenes to increase the floral aroma of wine without side activities that impact negatively on wine. Heterologous α-L-arabinofuranosidases and β-glucosidases have previously been expressed in S. cerevisiae and these studies have evaluated and found increased glycosidic activities against both natural and synthetic substrates. In this study, we expressed the Aspergillus awamori α-L-arabinofuranosidase (AwAbfB) in combination with either the β-glucosidases Bgl2 from Saccharomycopsis fibuligera or the BglA from Aspergillus kawachii in the industrial yeast strain S. cerevisiae VIN13 to facilitate the sequential enzymatic hydrolysis of monoterpene diglycosides. Enzyme assays and GC-FID (Gas Chromatography with a Flame Ionization Detector) results show a significant increase in the amount of free monoterpene concentrations under winemaking conditions in the strain co-expressing the AwAbfB and the Bgl2. The increases in free monoterpene levels obtained were similar to those obtained with a commercial enzyme preparation, LAFAZYM AROM. Sensorial evaluation confirmed the improvement in the wine aroma profile, particularly the floral character. This yeast strain permits a single culture fermentation which improves the sensorial quality and complexity of wine. Further investigations on the factors influencing the stability and reactivity of monoterpenes during alcoholic fermentation are needed.

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Doyle, Timothy Charles. "A fructose-intolerant yeast strain to select for sucrose fructosyl-transferase activity". Thesis, University of Oxford, 1993. http://ora.ox.ac.uk/objects/uuid:02236278-183d-4463-9732-f9e5f5e610b1.

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A selection system for yeast cells expressing mutated invertase (EC 3.2.1.26, SUC2) with altered fructotransferase activity was developed based on the survival of a fructose-intolerant strain in the presence of suitable acceptor substrates and sucrose. Cells of such a strain expressing a wild-type hydrolase activity will not grow due to the release of free fructose from sucrose. Cells expressing an inactive invertase mutant will not grow since they cannot cleave the sucrose, the sole carbon source. Only cells expressing sucrose fructosyl-transferase activity will thrive, growing on the released glucose, the fructosyl moiety not being released. A strain of Saccharomyces cerevisiae was engineered to be intolerant of the presence of fructose in its growth media. This was achieved by inducing a condition in yeast similar to liver cells of humans suffering from hereditary fructose intolerance (MIM 22960). This disorder results from a deficiency of aldolase B (EC 4.1.2.13), and phosphorylation of fructose by ketohexokinase (EC 2.7.1.3) results in an accumulation of fructose 1-phosphate, with a consequent depletion of cytoplasmic phosphate and ATP. Thus, cells in which ketohexokinase phosphorylates fructose, but which lack aldolase B, are intolerant of fructose. Yeast possess neither of these enzymes, and so expression of ketohexokinase in yeast would result in fructose-intolerance. A strain of yeast, for ketohexokinase expression, was initially bred to be unable to metabolize sucrose or fructose, yet remain capable of utilizing glucose, as well as lacking non-specific phosphatases, to prevent remobilization of sequestered fructose 1-phosphate. Rat liver ketohexokinase was purified to heterogeneity, and the partial amino acid sequence subsequently generated exploited to amplify a region of the ketohexokinase cDNA by PCR. This was used to probe a cDNA library, yielding clones encoding the entire ketohexokinase coding region. This was cloned into pMA91, and subsequent expression in yeast resulted in a strain intolerant of fructose in its growth medium, although still capable of growing on glucose. In order to produce a stable fructose-intolerant selection strain, a vector (pIADl) was constructed that allowed multiple integration of an expression cassette containing ketohexokinase cDNA into the rDNA locus of yeast chromosome XII. Expression of wild type invertase from the episomal plasmid pIAD3 in this strain resulted in sucrose-intolerance. A preliminary programme of mutagenesis of the SUC2 gene yielded eight libraries of about one hundred clones each. None of these contained any mutants showing solely sucrose fructosyl-transferase activity, although this system would clearly provide an ideal selection for such mutants from a much larger library.

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Gerebring, Linnéa. "Yeast Saccharomyces cerevisiae strain isolated from lager beer shows tolerance to isobutanol". Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-129066.

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The development of biofuels has received much attention due to the global warming and limited resources associated with fossil fuels. Butanol has been identified as a potential option due to its advantages over ethanol, for example higher energy density, compatibility with current infrastructure and its possibility to be blended with gasoline at any ratio. Yeast Saccharomyces cerevisiae can be used as a producer of butanol. However, butanol toxicity to the host limits the yield produced. In this study, four strains of yeast isolated from the habitats of lager beer, ale, wine and baker ́s yeast were grown in YPD media containing isobutanol concentrations of 1.5 %, 2 %, 3 % and 4 %. Growth was measured to determine the most tolerant strain. Gene expression for the genes RPN4, RTG1 and ILV2 was also measured, to determine its involvement in butanol stress. The genes have in previous studies seen to be involved in butanol tolerance or production, and the hypothesis was that they all should be upregulated in response to butanol exposure. It was found that the yeast strain isolated from lager beer was most tolerant to isobutanol concentrations of 2 % and 3 %. It was also found that the gene RPN4 was upregulated in response to isobutanol stress. There was no upregulation of RTG1 or ILV2, which was unexpected. The yeast strain isolated from lager beer and the gene RPN4 is proposed to be investigated further, to be able to engineer a suitable producer of the biofuel butanol.

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48

Swana, Jeffrey Ross. "Construction and Analysis of a Modified Yeast Strain for Next Generation Biofuel Production". Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-theses/52.

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Current research efforts are focused on 'second generation biofuels', which includes biofuels produced from lignocellulosic material. Lignocellulosic material is primarily composed of cellulose, a glucose polymer, xylose rich hemicellulose and non-fermentable lignin. Saccharomyces cerevisiae is widely used on an industrial scale for the production of ethanol from glucose; however, native S. cerevisiae does not contain the genes required for fermentation of xylose into ethanol. Others have sequentially expressed trans-genes from xylose fermenting organisms to engineer strains of S. cerevisiae capable of fermenting this pentose. The goal of this thesis was to generate a single cassette of 9 genes which have been shown to ferment xylose and arabinose. The 17 kb DNA fragment harboring all the genes necessary was introduced into the yeast genome using one-step homologous recombination based transformation. Expression of this cassette was verified by demonstrating that the first and last genes on this cassette were transcribed. The modified strain exhibited xylose utilization under microaerobic fermentation conditions. Further genetic and process engineering methods may be employed to improve the yield. The experiments described here demonstrate that generating a functional cassette of pentose fermenting genes is still achievable.

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49

Butler, Barbara L. "Separation of a brewing yeast strain of Saccharomyces cerevisiae based on cellular age". Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=78334.

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In yeast, aging appears to be marked by a progressive impairment in cellular mechanisms, resulting in irreversible changes in physiology and morphology. To date, very little has been reported about the biochemical changes that occur in yeast as a function of individual cell aging. To investigate this further, six generations of a brewing yeast strain of Saccharomyces cerevisiae (NCYC 1239) were separated according to cellular age using continuous phased culturing and biotin-streptavidin magnetic cell sorting.
To obtain cells with no bud scars (virgin cells), a concentrated yeast slurry was layered onto sucrose density gradients and centrifuged. The uppermost band from the gradients was collected and cells were biotinylated with biotinamidocaproate- N-hydroxysuccinimide ester, that covalently binds to lysine residues on the yeast cell wall. For continuous phased culturing, biotinylated cells were added to a carbon-limited nutrient medium and growth was synchronized using the doubling time of the cells. Harvested cells were incubated with streptavidin superparamagnetic beads and sorted with a strong permanent magnet. In total, approximately 75% of the biotinylated cells were recovered. Viability testing was conducted using vital staining and plate counts, with >98% viability reported with the vital stain and 37% viability with the agar plates.
In conclusion, continuous phased culture, together with magnetic cell sorting has the potential to become a powerful tool for the study of age-related biochemical changes in yeast. Further studies will focus on ensuring the reproducibility of the method and using the recovered cells to study biochemical changes occurring during yeasts' replicative lifespan.

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50

Gough, Suzanne. "Production of ethanol from molasses using the thermotolerant yeast strain Kluyveromyces marxianus IMB3". Thesis, University of Ulster, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284833.

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