Journal articles: 'Lignocellulosic inhibitor'

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Sjulander, Nikki, and Timo Kikas. "Origin, Impact and Control of Lignocellulosic Inhibitors in Bioethanol Production—A Review." Energies 13, no. 18 (September 11, 2020): 4751. http://dx.doi.org/10.3390/en13184751.

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Bioethanol production from lignocellulosic biomass is still struggling with many obstacles. One of them is lignocellulosic inhibitors. The aim of this review is to discuss the most known inhibitors. Additionally, the review addresses different detoxification methods to degrade or to remove inhibitors from lignocellulosic hydrolysates. Inhibitors are formed during the pretreatment of biomass. They derive from the structural polymers-cellulose, hemicellulose and lignin. The formation of inhibitors depends on the pretreatment conditions. Inhibitors can have a negative influence on both the enzymatic hydrolysis and fermentation of lignocellulosic hydrolysates. The inhibition mechanisms can be, for example, deactivation of enzymes or impairment of vital cell structures. The toxicity of each inhibitor depends on its chemical and physical properties. To decrease the negative effects of inhibitors, different detoxification methods have been researched. Those methods focus on the chemical modification of inhibitors into less toxic forms or on the separation of inhibitors from lignocellulosic hydrolysates. Each detoxification method has its limitations on the removal of certain inhibitors. To choose a suitable detoxification method, a deep molecular understanding of the inhibition mechanism and the inhibitor formation is necessary.

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Vanmarcke, Gert, Quinten Deparis, Ward Vanthienen, Arne Peetermans, Maria R. Foulquié-Moreno, and Johan M. Thevelein. "A novel AST2 mutation generated upon whole-genome transformation of Saccharomyces cerevisiae confers high tolerance to 5-Hydroxymethylfurfural (HMF) and other inhibitors." PLOS Genetics 17, no. 10 (October 8, 2021): e1009826. http://dx.doi.org/10.1371/journal.pgen.1009826.

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Development of cell factories for conversion of lignocellulosic biomass hydrolysates into biofuels or bio-based chemicals faces major challenges, including the presence of inhibitory chemicals derived from biomass hydrolysis or pretreatment. Extensive screening of 2526 Saccharomyces cerevisiae strains and 17 non-conventional yeast species identified a Candida glabrata strain as the most 5-hydroxymethylfurfural (HMF) tolerant. Whole-genome (WG) transformation of the second-generation industrial S. cerevisiae strain MD4 with genomic DNA from C. glabrata, but not from non-tolerant strains, allowed selection of stable transformants in the presence of HMF. Transformant GVM0 showed the highest HMF tolerance for growth on plates and in small-scale fermentations. Comparison of the WG sequence of MD4 and GVM1, a diploid segregant of GVM0 with similarly high HMF tolerance, surprisingly revealed only nine non-synonymous SNPs, of which none were present in the C. glabrata genome. Reciprocal hemizygosity analysis in diploid strain GVM1 revealed AST2N406I as the only causative mutation. This novel SNP improved tolerance to HMF, furfural and other inhibitors, when introduced in different yeast genetic backgrounds and both in synthetic media and lignocellulose hydrolysates. It stimulated disappearance of HMF and furfural from the medium and enhanced in vitro furfural NADH-dependent reducing activity. The corresponding mutation present in AST1 (i.e. AST1D405I) the paralog gene of AST2, also improved inhibitor tolerance but only in combination with AST2N406I and in presence of high inhibitor concentrations. Our work provides a powerful genetic tool to improve yeast inhibitor tolerance in lignocellulosic biomass hydrolysates and other inhibitor-rich industrial media, and it has revealed for the first time a clear function for Ast2 and Ast1 in inhibitor tolerance.

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Piva, Victor de Freitas, Vanessa Souza Reis Melo, Bruna Vieira Cabral, and Diego Andrade Lemos. "Extraction of furfural inhibitor from biomass hydrolysate of rice husk." Ciência e Natura 44 (April 18, 2022): e15. http://dx.doi.org/10.5902/2179460x68832.

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The production of second generation ethanol (E2G) has proven to be an alternative to non-renewable fuels, through transforming lignocellulosic waste into renewable fuel. In turn, rice husk has great potential due to its availability and composition. The conversion of lignocellulosic biomass to biofuel comprises a fundamental pre-treatment step, however, at this stage, the formation of degradation products (inhibitory compounds) occurs, among them, furfural, which cause negative effects on the viability of fermentative cells, making the production of E2G unfeasible. Given the above, the objective of this work was to remove the furfural inhibitor present in the lignocellulosic broth after the pre-treatment process, using oleic acid, through liquid-liquid extraction. The quantification of total reducing sugars in the hydrolyzate did not show significant variation between the pre and post extraction stages. Regarding the furfural inhibitor, in tests performed with a solution made in the laboratory, removal of up to 62.30% was obtained when the initial concentration was 5.00 g.L-1. With respect to the tests with the hydrolyzate from the rice husk pre-treatment, the maximum removal observed was 10.40%, but the initial concentration of furfural was 1.64 g.L-1. The results obtained indicate the possibility of using oleic acid as an extracting agent of the furfural inhibitor from lignocellulosic hydrolysates.

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Elgharbawy, Amal A. M., Md Zahangir Alam, Muhammad Moniruzzaman, and Hamzah Mohd Salleh. "Hydrolysis Kinetics of Oil Palm Empty Fruit Bunch in Ionic Liquids and Cellulase Integrated System." International Journal of Chemistry 11, no. 2 (July 26, 2019): 95. http://dx.doi.org/10.5539/ijc.v11n2p95.

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Ionic liquids (ILs) are developing as potential solvents in lignocellulose solvation, which enables cellulase accessibility into the substrate. Nevertheless, ILs could result in enzyme deactivation because of the high polarity. Therefore, developing a system of ILs-compatible cellulase (IL-E) to promote lignocellulose conversion into sugars is a challenge in ILs applications. This study used an IL-E to attain high conversion yield of sugars from oil palm empty fruit bunch (EFB). Cellulase (Tr-Cel) from Trichoderma reesei was stable in the ILs, 1-ethyl-3-methyl imidazolium diethyl phosphate [EMIM]DEP and choline acetate [Cho]OAc. The inhibition and deactivation of cellulase were evaluated using the model substrate, carboxymethyl cellulose (CMC) and EFB as a lignocellulosic material to assess the hydrolytic activity. The enzyme kinetics revealed that [Cho]OAc acted as a noncompetitive inhibitor. Additionally, [EMIM]DEP may not be considered as an inhibitor as it increases the Vmax and does not significantly affect the KM. In both cases, the study proved that IL did not result in a severe loss of cellulase activity, which is a promising outcome for one-pot hydrolysis of lignocellulosic materials.

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Westman, Johan O., Valeria Mapelli, Mohammad J. Taherzadeh, and Carl Johan Franzén. "Flocculation Causes Inhibitor Tolerance in Saccharomyces cerevisiae for Second-Generation Bioethanol Production." Applied and Environmental Microbiology 80, no. 22 (August 29, 2014): 6908–18. http://dx.doi.org/10.1128/aem.01906-14.

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ABSTRACTYeast has long been considered the microorganism of choice for second-generation bioethanol production due to its fermentative capacity and ethanol tolerance. However, tolerance toward inhibitors derived from lignocellulosic materials is still an issue. Flocculating yeast strains often perform relatively well in inhibitory media, but inhibitor tolerance has never been clearly linked to the actual flocculation abilityper se. In this study, variants of the flocculation geneFLO1were transformed into the genome of the nonflocculating laboratory yeast strainSaccharomyces cerevisiaeCEN.PK 113-7D. Three mutants with distinct differences in flocculation properties were isolated and characterized. The degree of flocculation and hydrophobicity of the cells were correlated to the length of the gene variant. The effect of different strength of flocculation on the fermentation performance of the strains was studied in defined medium with or without fermentation inhibitors, as well as in media based on dilute acid spruce hydrolysate. Strong flocculation aided against the readily convertible inhibitor furfural but not against less convertible inhibitors such as carboxylic acids. During fermentation of dilute acid spruce hydrolysate, the most strongly flocculating mutant with dense cell flocs showed significantly faster sugar consumption. The modified strain with the weakest flocculation showed a hexose consumption profile similar to the untransformed strain. These findings may explain why flocculation has evolved as a stress response and can find application in fermentation-based biorefinery processes on lignocellulosic raw materials.

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Roscini, Luca, Lorenzo Favaro, Laura Corte, Lorenzo Cagnin, Claudia Colabella, Marina Basaglia, Gianluigi Cardinali, and Sergio Casella. "A yeast metabolome-based model for an ecotoxicological approach in the management of lignocellulosic ethanol stillage." Royal Society Open Science 6, no. 1 (January 2019): 180718. http://dx.doi.org/10.1098/rsos.180718.

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Lignocellulosic bioethanol production results in huge amounts of stillage, a potentially polluting by-product. Stillage, rich in heavy metals and, mainly, inhibitors, requires specific toxicity studies to be adequately managed. To this purpose, we applied an FTIR ecotoxicological bioassay to evaluate the toxicity of lignocellulosic stillage. Two weak acids and furans, most frequently found in lignocellulosic stillage, have been tested in different mixtures against three Saccharomyces cerevisiae strains. The metabolomic reaction of the test microbes and the mortality induced at various levels of inhibitor concentration showed that the strains are representative of three different types of response. Furthermore, the relationship between concentrations and FTIR synthetic stress indexes has been studied, with the aim of defining a model able to predict the concentrations of inhibitors in stillage, resulting in an optimized predictive model for all the strains. This approach represents a promising tool to support the ecotoxicological management of lignocellulosic stillage.

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Padmapriya, G., V. Dhivya, M. Vishal, Y. A. J. Roshni, T. Akila, and S. Ramalingam. "Development of tolerance to aldehyde-based inhibitors of pretreated lignocellulosic biomass sugars in E. coli MG1655 by sequential batch adaptive evolution." Journal of Environmental Biology 42, no. 5 (September 27, 2021): 1239–48. http://dx.doi.org/10.22438/jeb/42/5/mrn-1812.

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Aim: The current study involved carrying out adaptive evolution to inculcate tolerance to hydrolysate-derived aldehyde-based inhibitors, furfural, vanillin, syringaldehyde and 4-hydroxybenzaldehyde (4-HB) for the valorization of pretreated lignocellulosic biomass. Methodology: The growth-inhibitory effects of the aforementioned inhibitors on E. coli MG1655 were investigated. The percentage of inhibition was calculated from the initial growth, followed by extrapolating the IC50 values for each inhibitor. Based on these findings, adaptation experiments were conducted for individual inhibitors at a concentration lesser than or closer to IC50. Results: The specific growth rate of cells was lowered by 2.2-, 3-, 1.3- and 5- fold when grown in the presence of furfural, vanillin, syringaldehyde and 4- hydroxybenzaldehyde (4-HB), respectively. The adapted strains which were grown in the presence of furfural (9mM), vanillin (9mM), syringaldehyde (8mM) and 4- HB (6mM) individually showed around 1.5 -2.5- fold increase in the specific growth rate as compared to the wild-type with decreased lag phases and increased final cell densities. Interpretation: The strains, subjected to adaptive evolution, resulted in increased tolerance to single inhibitors and these will further be sequentially adapted to other three inhibitors for their utilization in the valorization of pretreated lignocellulosic biomass.

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Chanda, Kakoli, Atifa Begum Mozumder, Ringhoilal Chorei, Ridip Kumar Gogoi, and Himanshu Kishore Prasad. "A Lignocellulolytic Colletotrichum sp. OH with Broad-Spectrum Tolerance to Lignocellulosic Pretreatment Compounds and Derivatives and the Efficiency to Produce Hydrogen Peroxide and 5-Hydroxymethylfurfural Tolerant Cellulases." Journal of Fungi 7, no. 10 (September 22, 2021): 785. http://dx.doi.org/10.3390/jof7100785.

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Fungal endophytes are an emerging source of novel traits and biomolecules suitable for lignocellulosic biomass treatment. This work documents the toxicity tolerance of Colletotrichum sp. OH toward various lignocellulosic pretreatment-derived inhibitors. The effects of aldehydes (vanillin, p-hydroxybenzaldehyde, furfural, 5-hydroxymethylfurfural; HMF), acids (gallic, formic, levulinic, and p-hydroxybenzoic acid), phenolics (hydroquinone, p-coumaric acid), and two pretreatment chemicals (hydrogen peroxide and ionic liquid), on the mycelium growth, biomass accumulation, and lignocellulolytic enzyme activities, were tested. The reported Colletotrichum sp. OH was naturally tolerant to high concentrations of single inhibitors like HMF (IC50; 17.5 mM), levulinic acid (IC50; 29.7 mM), hydroquinone (IC50; 10.76 mM), and H2O2 (IC50; 50 mM). The lignocellulolytic enzymes displayed a wide range of single and mixed inhibitor tolerance profiles. The enzymes β-glucosidase and endoglucanase showed H2O2- and HMF-dependent activity enhancements. The enzyme β-glucosidase activity was 34% higher in 75 mM and retained 20% activity in 125 mM H2O2. Further, β-glucosidase activity increased to 24 and 32% in the presence of 17.76 and 8.8 mM HMF. This research suggests that the Colletotrichum sp. OH, or its enzymes, can be used to pretreat plant biomass, hydrolyze it, and remove inhibitory by-products.

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Greetham, Darren, Abdelrahman Saleh Zaky, and Chenyu Du. "Exploring the tolerance of marine yeast to inhibitory compounds for improving bioethanol production." Sustainable Energy & Fuels 3, no. 6 (2019): 1545–53. http://dx.doi.org/10.1039/c9se00029a.

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Lam, Felix H., Burcu Turanlı-Yıldız, Dany Liu, Michael G. Resch, Gerald R. Fink, and Gregory Stephanopoulos. "Engineered yeast tolerance enables efficient production from toxified lignocellulosic feedstocks." Science Advances 7, no. 26 (June 2021): eabf7613. http://dx.doi.org/10.1126/sciadv.abf7613.

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Lignocellulosic biomass remains unharnessed for the production of renewable fuels and chemicals due to challenges in deconstruction and the toxicity its hydrolysates pose to fermentation microorganisms. Here, we show in Saccharomyces cerevisiae that engineered aldehyde reduction and elevated extracellular potassium and pH are sufficient to enable near-parity production between inhibitor-laden and inhibitor-free feedstocks. By specifically targeting the universal hydrolysate inhibitors, a single strain is enhanced to tolerate a broad diversity of highly toxified genuine feedstocks and consistently achieve industrial-scale titers (cellulosic ethanol of >100 grams per liter when toxified). Furthermore, a functionally orthogonal, lightweight design enables seamless transferability to existing metabolically engineered chassis strains: We endow full, multifeedstock tolerance on a xylose-consuming strain and one producing the biodegradable plastics precursor lactic acid. The demonstration of “drop-in” hydrolysate competence enables the potential of cost-effective, at-scale biomass utilization for cellulosic fuel and nonfuel products alike.

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Ma, Kedong, Mingxiong He, Huiyan You, Liwei Pan, Guoquan Hu, Yubo Cui, and Toshinari Maeda. "Enhanced fuel ethanol production from rice straw hydrolysate by an inhibitor-tolerant mutant strain of Scheffersomyces stipitis." RSC Advances 7, no. 50 (2017): 31180–88. http://dx.doi.org/10.1039/c7ra04049k.

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Bertini, Alessandro, Mattia Gelosia, Gianluca Cavalaglio, Marco Barbanera, Tommaso Giannoni, Giorgia Tasselli, Andrea Nicolini, and Franco Cotana. "Production of Carbohydrates from Cardoon Pre-Treated by Acid-Catalyzed Steam Explosion and Enzymatic Hydrolysis." Energies 12, no. 22 (November 11, 2019): 4288. http://dx.doi.org/10.3390/en12224288.

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Cardoon (Cynara cardunculus) is a promising crop from which to obtain oilseeds and lignocellulosic biomass. Acid-catalyzed steam explosion is a thermochemical process that can efficiently pre-treat lignocellulosic biomass. The drawback is the production of a high number of carbohydrate degradation products in the liquid fraction that could inhibit microbial growth. In this work, the lignocellulosic biomass of cardoon, gathered from a dedicated field, were used as the raw material for the production of fermentable monosaccharides by employing acid-catalyzed steam explosion. The raw material was pre-soaked with a dilute 1% (w/w) sulfuric acid solution and then subjected to steam explosion under three different severity conditions. The recovered slurry was separated into solid and liquid fractions, which were individually characterized to determine total carbohydrate and inhibitor concentrations. The slurry and the washed solid fraction underwent enzymatic hydrolysis to release glucose and pentose monosaccharides. By conducting the pre-treatment at 175 °C for 35 min and hydrolyzing the obtained slurry, a yield of 33.17 g of monosaccharides/100 g of cardoon was achieved. At the same conditions, 4.39 g of inhibitors/100 g of cardoon were produced.

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Bhatt, Sheelendra M., and Shilpa. "Lignocellulosic feedstock conversion, inhibitor detoxification and cellulosic hydrolysis – a review." Biofuels 5, no. 6 (November 2, 2014): 633–49. http://dx.doi.org/10.1080/17597269.2014.1003702.

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Liu, Zonglin Lewis, Jaewoong Moon, and Mingzhou Joe Song. "Genomic mechanisms of inhibitor-detoxification for low-cost lignocellulosic bioethanol conversion." Journal of Biotechnology 136 (October 2008): S218. http://dx.doi.org/10.1016/j.jbiotec.2008.07.460.

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Thontowi, Ahmad. "Evaluation of Non-Saccharomyces Cerevisiae Strains Isolated from Sea Water Against Inhibitory Compounds for Ethanol Production." Squalen Bulletin of Marine and Fisheries Postharvest and Biotechnology 12, no. 2 (August 5, 2017): 57. http://dx.doi.org/10.15578/squalen.v12i2.284.

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An important parameter in industrial bioethanol fermentation is the resistance of yeast to osmotic pressure and inhibitor compounds. Aureobasidium pullulans LBF-3-0074 and Schwanniomyces etchellsii LBF-3-0034 are reported capable to produce ethanol. LBF-3-0034 and LBF-3-0074 are yeast strains isolated from Bali and Lombok sea water. This study aimed to evaluate characteristics of both LBF-3-0034 and LBF-3-0074 strains under the effects of glucose and inhibitor compounds. Both strains were allowed to consume glucose up to 120 mM. Then, these strains were grown with the present of several inhibitors, i.e. 5-hydroxymethyl-2-furaldehyde (5-HMF), furfural, acetic acid, formic acid, and levulinic acid. Results showed that the two yeast strains studied could grow and ferment the sugars under both osmotic and inhibitor stress conditions. As conclusion, Schwanniomyces etchellsii LBF-3-0034 and Aureobasidium pullulans LBF-3-0074 are potential for direct fermentation of lignocellulosic hydrolysate to ethanol.

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Riyanti, Eny Ida, and Edy Listanto. "INHIBITION OF THE GROWTH OF TOLERANT YEAST Saccharomyces cerevisiae STRAIN I136 BY A MIXTURE OF SYNTHETIC INHIBITORS." Indonesian Journal of Agricultural Science 18, no. 1 (September 14, 2017): 17. http://dx.doi.org/10.21082/ijas.v18n1.2017.p17-24.

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<p>Biomass from lignocellulosic wastes is a potential source for biobased products. However, one of the constraints in utilization of biomass hydrolysate is the presence of inhibitors. Therefore, the use of inhibitor-tolerant microorganisms in the fermentation is required. The study aimed to investigate the effect of a mixture of inhibitors on the growth of Saccharomyces cerevisiae strain I136 grown in medium containing synthetic inhibitors (acetic acid, formic acid, furfural, 5-hydroxymethyl furfural/5-HMF, and levulinic acid) in four different concentrations with a mixture of carbon sources, glucose (50 g.l-1) and xylose (50 g.l-1) at 30oC. The parameters related to growth and fermentation products were observed. Results showed that the strain was able to grow in media containing natural inhibitors (BSL medium) with µmax of 0.020/h. Higher level of synthetic inhibitors prolonged the lag phase, decreased the cell biomass and ethanol production, and specific growth rate. The strain could detoxify furfural and 5-HMF and produced the highest ethanol (Y(p/s) of 0.32 g.g-1) when grown in BSL. Glucose was utilized as its level decreased in a result of increase in cell biomass, in contrast to xylose which was not consumed. The highest cell biomass was produced in YNB with Y (x/s) value of 0.25 g.g-1. The strain produced acetic acid as a dominant side product and could convert furfural into a less toxic compound, hydroxyl furfural. This robust tolerant strain provides basic information on resistance mechanism and would be useful for bio-based cell factory using lignocellulosic materials. </p>

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Tesfaw, Asmamaw, and Fassil Assefa. "Current Trends in Bioethanol Production by Saccharomyces cerevisiae: Substrate, Inhibitor Reduction, Growth Variables, Coculture, and Immobilization." International Scholarly Research Notices 2014 (December 8, 2014): 1–11. http://dx.doi.org/10.1155/2014/532852.

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Bioethanol is one of the most commonly used biofuels in transportation sector to reduce greenhouse gases. S. cerevisiae is the most employed yeast for ethanol production at industrial level though ethanol is produced by an array of other yeasts, bacteria, and fungi. This paper reviews the current and nonmolecular trends in ethanol production using S. cerevisiae. Ethanol has been produced from wide range of substrates such as molasses, starch based substrate, sweet sorghum cane extract, lignocellulose, and other wastes. The inhibitors in lignocellulosic hydrolysates can be reduced by repeated sequential fermentation, treatment with reducing agents and activated charcoal, overliming, anion exchanger, evaporation, enzymatic treatment with peroxidase and laccase, in situ detoxification by fermenting microbes, and different extraction methods. Coculturing S. cerevisiae with other yeasts or microbes is targeted to optimize ethanol production, shorten fermentation time, and reduce process cost. Immobilization of yeast cells has been considered as potential alternative for enhancing ethanol productivity, because immobilizing yeasts reduce risk of contamination, make the separation of cell mass from the bulk liquid easy, retain stability of cell activities, minimize production costs, enable biocatalyst recycling, reduce fermentation time, and protect the cells from inhibitors. The effects of growth variables of the yeast and supplementation of external nitrogen sources on ethanol optimization are also reviewed.

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Tu, Wei-Lin, Tien-Yang Ma, Chung-Mao Ou, Gia-Luen Guo, and Yu Chao. "Simultaneous saccharification and co-fermentation with a thermotolerant Saccharomyces cerevisiae to produce ethanol from sugarcane bagasse under high temperature conditions." BioResources 16, no. 1 (January 5, 2021): 1358–72. http://dx.doi.org/10.15376/biores.16.1.1358-1372.

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Lignocellulosic ethanol production at high temperature offers advantages such as the decrease of contamination risk and cooling cost. Recombinant xylose-fermenting Saccharomyces cerevisiae has been considered a promising strain for ethanol production from lignocellulose for its high inhibitor tolerance and superior capability to ferment glucose and xylose into ethanol. To improve the ethanolic fermentation by xylose at high temperature, the strain YY5A was subjected to the ethyl methanesulfonate (EMS) mutagenesis. A mutant strain T5 was selected from the EMS-treated cultures to produce ethanol. However, the xylose uptake by T5 was severely inhibited by the high ethanol concentration during the co-fermentation in defined YPDX medium at 40 °C. In this study, the simultaneous saccharification and co-fermentation (SSCF) and the separate hydrolysis and co-fermentation (SHCF) processes of sugarcane bagasse were assessed to solve this problem. The xylose utilization by T5 was remarkably improved using the SSCF process compared to the SHCF process. For the SHCF and SSCF processes, 48% and 99% of the xylose in the hydrolysate was consumed at 40 °C, respectively. The ethanol yield was enhanced by the SSCF process. The ethanol production can reach to 36.0 g/L using this process under high-temperature conditions.

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Teixeira, Vanessa S., Suéllen P. H. Azambuja, Priscila H. Carvalho, Fátima A. A. Costa, Patricia R. Kitaka, Claudia Stekelgerb, Silvio R. Andrietta, Maria G. S. Andrietta, and Rosana Goldbeck. "Robustness and Ethanol Production of Industrial Strains of Saccharomyces cerevisiae Using Different Sugarcane Bagasse Hydrolysates." Journal of Applied Biotechnology 7, no. 1 (May 7, 2019): 23. http://dx.doi.org/10.5296/jab.v7i1.14599.

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Sugarcane bagasse is one of the main lignocellulosic raw materials used for the production of second-generation ethanol. Technological studies on fermentation processes have focused on the search for and development of more robust microorganisms that are able to produce bioethanol efficiently and are resistant to the main fermentation inhibitors. The purpose of this study was to evaluate the robustness and ethanol production of industrial strains of Saccharomyces cerevisiae using acid, alkaline, and enzymatic sugarcane bagasse hydrolysates. Hydrolysis was carried out to release fermentable sugars from sugarcane bagasse. Fermentations were performed in shake flasks containing sugarcane hydrolysates supplemented with 150 g L−1 glucose to evaluate the kinetic parameters of the reaction. Inhibitor tolerance was evaluated by incubating cells with different concentrations of inhibitors in 96-well plates. The biomass yield on substrate, ethanol yield on substrate, and ethanol productivity of the six strains were higher in 0.5% acid, 0.5% alkaline, and enzymatic hydrolysates (i.e., under milder conditions). The SA-1 (Santa Adélia-1) strain had a better performance in comparison with the other strains for its ability to produce ethanol in a very severe condition (7% acid hydrolysis) and for its robustness in growing at several inhibitor concentrations.

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Yan, Xiongying, Xia Wang, Yongfu Yang, Zhen Wang, Haoyu Zhang, Yang Li, Qiaoning He, Mian Li, and Shihui Yang. "Cysteine supplementation enhanced inhibitor tolerance of Zymomonas mobilis for economic lignocellulosic bioethanol production." Bioresource Technology 349 (April 2022): 126878. http://dx.doi.org/10.1016/j.biortech.2022.126878.

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Wongsurakul, Peerawat, Mutsee Termtanun, Worapon Kiatkittipong, Jun Wei Lim, Kunlanan Kiatkittipong, Prasert Pavasant, Izumi Kumakiri, and Suttichai Assabumrungrat. "Comprehensive Review on Potential Contamination in Fuel Ethanol Production with Proposed Specific Guideline Criteria." Energies 15, no. 9 (April 20, 2022): 2986. http://dx.doi.org/10.3390/en15092986.

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Ethanol is a promising biofuel that can replace fossil fuel, mitigate greenhouse gas (GHG) emissions, and represent a renewable building block for biochemical production. Ethanol can be produced from various feedstocks. First-generation ethanol is mainly produced from sugar- and starch-containing feedstocks. For second-generation ethanol, lignocellulosic biomass is used as a feedstock. Typically, ethanol production contains four major steps, including the conversion of feedstock, fermentation, ethanol recovery, and ethanol storage. Each feedstock requires different procedures for its conversion to fermentable sugar. Lignocellulosic biomass requires extra pretreatment compared to sugar and starch feedstocks to disrupt the structure and improve enzymatic hydrolysis efficiency. Many pretreatment methods are available such as physical, chemical, physicochemical, and biological methods. However, the greatest concern regarding the pretreatment process is inhibitor formation, which might retard enzymatic hydrolysis and fermentation. The main inhibitors are furan derivatives, aromatic compounds, and organic acids. Actions to minimize the effects of inhibitors, detoxification, changing fermentation strategies, and metabolic engineering can subsequently be conducted. In addition to the inhibitors from pretreatment, chemicals used during the pretreatment and fermentation of byproducts may remain in the final product if they are not removed by ethanol distillation and dehydration. Maintaining the quality of ethanol during storage is another concerning issue. Initial impurities of ethanol being stored and its nature, including hygroscopic, high oxygen and carbon dioxide solubility, influence chemical reactions during the storage period and change ethanol’s characteristics (e.g., water content, ethanol content, acidity, pH, and electrical conductivity). During ethanol storage periods, nitrogen blanketing and corrosion inhibitors can be applied to reduce the quality degradation rate, the selection of which depends on several factors, such as cost and storage duration. This review article sheds light on the techniques of control used in ethanol fuel production, and also includes specific guidelines to control ethanol quality during production and the storage period in order to preserve ethanol production from first-generation to second-generation feedstock. Finally, the understanding of impurity/inhibitor formation and controlled strategies is crucial. These need to be considered when driving higher ethanol blending mandates in the short term, utilizing ethanol as a renewable building block for chemicals, or adopting ethanol as a hydrogen carrier for the long-term future, as has been recommended.

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Nilsson, Anneli, Marie F. Gorwa-Grauslund, Bärbel Hahn-Hägerdal, and Gunnar Lidén. "Cofactor Dependence in Furan Reduction by Saccharomyces cerevisiae in Fermentation of Acid-Hydrolyzed Lignocellulose." Applied and Environmental Microbiology 71, no. 12 (December 2005): 7866–71. http://dx.doi.org/10.1128/aem.71.12.7866-7871.2005.

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ABSTRACT A decreased fermentation rate due to inhibition is a significant problem for economic conversion of acid-pretreated lignocellulose hydrolysates to ethanol, since the inhibition gives rise to a requirement for separate detoxification steps. Together with acetic acid, the sugar degradation products furfural and 5-hydroxymethyl furfural are the inhibiting compounds found at the highest concentrations in hydrolysates. These aldehydes have been shown to affect both the specific growth rate and the rate of fermentation by yeast. Two strains of Saccharomyces cerevisiae with different abilities to ferment inhibiting hydrolysates were evaluated in fermentations of a dilute acid hydrolysate from spruce, and the reducing activities for furfural and 5-hydroxymethyl furfural were determined. Crude cell extracts of a hydrolysate-tolerant strain (TMB3000) converted both furfural and 5-hydroxymethyl furfural to the corresponding alcohol at a rate that was severalfold higher than the rate observed for cell extracts of a less tolerant strain (CBS 8066), thereby confirming that there is a correlation between the fermentation rate in a lignocellulosic hydrolysate and the bioconversion capacity of a strain. The in vitro NADH-dependent furfural reduction capacity of TMB3000 was three times higher than that of CBS 8066 (1,200 mU/mg protein and 370 mU/mg protein, respectively) in fed-batch experiments. Furthermore, the inhibitor-tolerant strain TMB3000 displayed a previously unknown NADH-dependent reducing activity for 5-hydroxymethyl furfural (400 mU/mg protein during fed-batch fermentation of hydrolysates). No corresponding activity was found in strain CBS 8066 (<2 mU/mg). The ability to reduce 5-hydroxymethyl furfural is an important characteristic for the development of yeast strains with increased tolerance to lignocellulosic hydrolysates.

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Jansen, Trudy, Justin Wallace Hoff, Neil Jolly, and Willem Heber van Zyl. "Mating of natural Saccharomyces cerevisiae strains for improved glucose fermentation and lignocellulosic inhibitor tolerance." Folia Microbiologica 63, no. 2 (September 8, 2017): 155–68. http://dx.doi.org/10.1007/s12223-017-0546-3.

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Zhou, Long, Fabio Santomauro, Jiajun Fan, Duncan Macquarrie, James Clark, Christopher J. Chuck, and Vitaliy Budarin. "Fast microwave-assisted acidolysis: a new biorefinery approach for the zero-waste utilisation of lignocellulosic biomass to produce high quality lignin and fermentable saccharides." Faraday Discussions 202 (2017): 351–70. http://dx.doi.org/10.1039/c7fd00102a.

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Generally, biorefineries convert lignocellulosic biomass into a range of biofuels and further value added chemicals. However, conventional biorefinery processes focus mainly on the cellulose and hemicellulose fractions and therefore produce only low quality lignin, which is commonly burnt to provide process heat. To make full use of the biomass, more attention needs to be focused on novel separation techniques, where high quality lignin can be isolated that is suitable for further valorisation into aromatic chemicals and fuel components. In this paper, three types of lignocellulosic biomass (softwood, hardwood and herbaceous biomass) were processed by microwave-assisted acidolysis to produce high quality lignin. The lignin from the softwood was isolated largely intact in the solid residue after acidolysis. For example, a 10 min microwave-assisted acidolysis treatment produced lignin with a purity of 93% and in a yield of 82%, which is superior to other conventional separation methods reported. Furthermore, py-GC/MS analysis proved that the isolated lignin retained the original structure of native lignin in the feedstock without severe chemical modification. This is a large advantage, and the purified lignin is suitable for further chemical processing. To assess the suitability of this methodology as part of a biorefinery system, the aqueous phase, produced after acidolysis of the softwood, was characterised and assessed for its suitability for fermentation. The broth contained some mono- and di-saccharides but mainly contained organic acids, oligosaccharides and furans. While this is unsuitable for S. cerevisiae and other common ethanol producing yeasts, two oleaginous yeasts with known inhibitor tolerances were selected: Cryptococcus curvatus and Metschnikowia pulcherrima. Both yeasts could grow on the broth, and demonstrated suitable catabolism of the oligosaccharides and inhibitors over 7 days. In addition, both yeasts were shown to be able to produce an oil with a similar composition to that of palm oil. This preliminary work demonstrates new protocols of microwave-assisted acidolysis and therefore offers an effective approach to produce high purity lignin and fermentable chemicals, which is a key step towards developing a zero-waste lignocellulosic biorefinery.

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Wang, Yanan, Peng Zhan, Lishu Shao, Lin Zhang, and Yan Qing. "Effects of Inhibitors Generated by Dilute Phosphoric Acid Plus Steam-Exploded Poplar on Saccharomyces cerevisiae Growth." Microorganisms 10, no. 7 (July 19, 2022): 1456. http://dx.doi.org/10.3390/microorganisms10071456.

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The pretreatment of lignocellulosic biomass is important for efficient bioethanol conversion, but causes undesirable by-products that inhibit microbial growth, conversely affecting the bioconversion efficiency. In this study, the main inhibitors derived from dilute phosphoric acid plus steam-exploded poplar wood were identified as 0.22 g/L furfural, 3.63 g/L acetic acid, 0.08 g/L syringaldehyde, etc., indicating the green nature and low toxicity of the pretreatment process. The effects of the three typical inhibitors (furfural, acetic acid, and syringaldehyde) on Saccharomyces cerevisiae 1517RM growth were analyzed and shown to prolong the lag phase of microbial growth to different degrees. In all the inhibitor groups, the ergosterol secretion was boosted, indicating low cell membrane fluidity and robustness of the strain to an adverse environment. The cell electronegativity and morphology of S. cerevisiae 1517RM also changed under different growth conditions, which was helpful for monitoring the physicochemical properties of cells. Furfural, acetic acid, and syringaldehyde had a synergistic effect on each other, providing an important reference to improving the subsequent ethanol fermentation process.

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Cavalaglio, Gianluca, Mattia Gelosia, Tommaso Giannoni, Ramoon Barros Lovate Temporim, Andrea Nicolini, Franco Cotana, and Alessandro Bertini. "Acid-catalyzed steam explosion for high enzymatic saccharification and low inhibitor release from lignocellulosic cardoon stalks." Biochemical Engineering Journal 174 (October 2021): 108121. http://dx.doi.org/10.1016/j.bej.2021.108121.

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Singhania, Reeta Rani, Anil Kumar Patel, Tirath Raj, Mei-Ling Tsai, Chiu-Wen Chen, and Cheng-Di Dong. "Advances and Challenges in Biocatalysts Application for High Solid-Loading of Biomass for 2nd Generation Bio-Ethanol Production." Catalysts 12, no. 6 (June 3, 2022): 615. http://dx.doi.org/10.3390/catal12060615.

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Growth in population and thereby increased industrialization to meet its requirement, has elevated significantly the demand for energy resources. Depletion of fossil fuel and environmental sustainability issues encouraged the exploration of alternative renewable eco-friendly fuel resources. Among major alternative fuels, bio-ethanol produced from lignocellulosic biomass is the most popular one. Lignocellulosic biomass is the most abundant renewable resource which is ubiquitous on our planet. All the plant biomass is lignocellulosic which is composed of cellulose, hemicellulose and lignin, intricately linked to each other. Filamentous fungi are known to secrete a plethora of biomass hydrolyzing enzymes. Mostly these enzymes are inducible, hence the fungi secrete them economically which causes challenges in their hyperproduction. Biomass’s complicated structure also throws challenges for which pre-treatments of biomass are necessary to make the biomass amorphous to be accessible for the enzymes to act on it. The enzymatic hydrolysis of biomass is the most sustainable way for fermentable sugar generation to convert into ethanol. To have sufficient ethanol concentration in the broth for efficient distillation, high solid loading ~<20% of biomass is desirable and is the crux of the whole technology. High solid loading offers several benefits including a high concentration of sugars in broth, low equipment sizing, saving cost on infrastructure, etc. Along with the benefits, several challenges also emerged simultaneously, like issues of mass transfer, low reaction rate due to water constrains in, high inhibitor concentration, non-productive binding of enzyme lignin, etc. This article will give an insight into the challenges for cellulase action on cellulosic biomass at a high solid loading of biomass and its probable solutions.

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Luo, Xingxing, Baiquan Zeng, Yanan Zhong, and Jienan Chen. "Production and detoxification of inhibitors during the destruction of lignocellulose spatial structure." BioResources 17, no. 1 (December 9, 2021): 1939–61. http://dx.doi.org/10.15376/biores.17.1.luo.

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Lignocellulosic biomass is a renewable resource that is widely abundant and can be used to produce biofuels such as methanol and ethanol. Because biofuels have the potential to alleviate shortages of energy in today’s world, they have attracted much research attention. The pretreatment of lignocellulose is an important step in the conversion of biomass products. The pretreatment can destroy the crosslinking effect of lignin and hemicellulose on cellulose, remove lignin, degrade hemicellulose, and change the crystal structure of cellulose. The reaction area between the enzyme and the substrate is enlarged, and the yield of subsequent enzymatic hydrolysis and microbial fermentation products is significantly increased. Conventional pretreatment methods help convert lignocellulosic material to sugars, but the treatments also produce some inhibitors, which are mainly organic acids, aldehydes, phenols, and other substances. They may affect the subsequent saccharification and growth of fermentation microorganisms, thereby reducing the bioconversion of the lignocellulose. It is therefore necessary to take effective means of detoxification. This paper reviews lignocellulose pretreatment methods, with an emphasis on inhibitors and their management. A summary is provided of detoxification methods, and the future use of lignocellulosic biomass for fuels prospects.

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Abdel-Rahman, Mohamed Ali, Saad El-Din Hassan, Amr Fouda, Ahmed A. Radwan, Mohammed G. Barghoth, and Salha G. Desouky. "Evaluating the Effect of Lignocellulose-Derived Microbial Inhibitors on the Growth and Lactic Acid Production by Bacillus coagulans Azu-10." Fermentation 7, no. 1 (January 27, 2021): 17. http://dx.doi.org/10.3390/fermentation7010017.

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Effective lactic acid (LA) production from lignocellulosic biomass materials is challenged by several limitations related to pentose sugar utilization, inhibitory compounds, and/or fermentation conditions. In this study, a newly isolated Bacillus coagulans strain Azu-10 was obtained and showed homofermentative LA production from xylose with optimal fermentation conditions at 50 °C and pH 7.0. Growth of strain Azu-10 and LA-fermentation efficiency were evaluated in the presence of various lignocellulose-derived inhibitors (furans, carboxylic acids, and phenols) at different concentrations. Furanic lignocellulosic-derived inhibitors were completely detoxified. The strain has exhibited high biomass, complete xylose consumption, and high LA production in the presence of 1.0–4.0 g/L furfural and 1.0–5.0 g/L of hydroxymethyl furfural, separately. Moreover, strain Azu-10 exhibited high LA production in the presence of 5.0–15.0 g/L acetic acid, 5.0 g/L of formic acid, and up to 7.0 g/L of levulinic acid, separately. Besides, for phenolic compounds, p-coumaric acid was most toxic at 1.0 g/L, while syringaldehyde or p-hydroxybenzaldehyde, and vanillin at 1.0 g/L did not inhibit LA fermentation. The present study provides an interesting potential candidate for the thermophilic LA fermentation from lignocellulose-derived substrates at the industrial biorefinery level.

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Lin, Feng-Ming, Bin Qiao, and Ying-Jin Yuan. "Comparative Proteomic Analysis of Tolerance and Adaptation of Ethanologenic Saccharomyces cerevisiae to Furfural, a Lignocellulosic Inhibitory Compound." Applied and Environmental Microbiology 75, no. 11 (April 10, 2009): 3765–76. http://dx.doi.org/10.1128/aem.02594-08.

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ABSTRACT The molecular mechanism involved in tolerance and adaptation of ethanologenic Saccharomyces cerevisiae to inhibitors (such as furfural, acetic acid, and phenol) represented in lignocellulosic hydrolysate is still unclear. Here, 18O-labeling-aided shotgun comparative proteome analysis was applied to study the global protein expression profiles of S. cerevisiae under conditions of treatment of furfural compared with furfural-free fermentation profiles. Proteins involved in glucose fermentation and/or the tricarboxylic acid cycle were upregulated in cells treated with furfural compared with the control cells, while proteins involved in glycerol biosynthesis were downregulated. Differential levels of expression of alcohol dehydrogenases were observed. On the other hand, the levels of NADH, NAD+, and NADH/NAD+ were reduced whereas the levels of ATP and ADP were increased. These observations indicate that central carbon metabolism, levels of alcohol dehydrogenases, and the redox balance may be related to tolerance of ethanologenic yeast for and adaptation to furfural. Furthermore, proteins involved in stress response, including the unfolded protein response, oxidative stress, osmotic and salt stress, DNA damage and nutrient starvation, were differentially expressed, a finding that was validated by quantitative real-time reverse transcription-PCR to further confirm that the general stress responses are essential for cellular defense against furfural. These insights into the response of yeast to the presence of furfural will benefit the design and development of inhibitor-tolerant ethanologenic yeast by metabolic engineering or synthetic biology.

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Sato, Trey K., Tongjun Liu, Lucas S. Parreiras, Daniel L. Williams, Dana J. Wohlbach, Benjamin D. Bice, Irene M. Ong, et al. "Harnessing Genetic Diversity in Saccharomyces cerevisiae for Fermentation of Xylose in Hydrolysates of Alkaline Hydrogen Peroxide-Pretreated Biomass." Applied and Environmental Microbiology 80, no. 2 (November 8, 2013): 540–54. http://dx.doi.org/10.1128/aem.01885-13.

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ABSTRACTThe fermentation of lignocellulose-derived sugars, particularly xylose, into ethanol by the yeastSaccharomyces cerevisiaeis known to be inhibited by compounds produced during feedstock pretreatment. We devised a strategy that combined chemical profiling of pretreated feedstocks, high-throughput phenotyping of genetically diverseS. cerevisiaestrains isolated from a range of ecological niches, and directed engineering and evolution against identified inhibitors to produce strains with improved fermentation properties. We identified and quantified for the first time the major inhibitory compounds in alkaline hydrogen peroxide (AHP)-pretreated lignocellulosic hydrolysates, including Na+, acetate, andp-coumaric (pCA) and ferulic (FA) acids. By phenotyping these yeast strains for their abilities to grow in the presence of these AHP inhibitors, one heterozygous diploid strain tolerant to all four inhibitors was selected, engineered for xylose metabolism, and then allowed to evolve on xylose with increasing amounts ofpCA and FA. After only 149 generations, one evolved isolate, GLBRCY87, exhibited faster xylose uptake rates in both laboratory media and AHP switchgrass hydrolysate than its ancestral GLBRCY73 strain and completely converted 115 g/liter of total sugars in undetoxified AHP hydrolysate into more than 40 g/liter ethanol. Strikingly, genome sequencing revealed that during the evolution from GLBRCY73, the GLBRCY87 strain acquired the conversion of heterozygous to homozygous alleles in chromosome VII and amplification of chromosome XIV. Our approach highlights that simultaneous selection on xylose andpCA or FA with a wildS. cerevisiaestrain containing inherent tolerance to AHP pretreatment inhibitors has potential for rapid evolution of robust properties in lignocellulosic biofuel production.

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Chen, Kun, Long Jun Xu, and Jun Yi. "Bioconversion of Lignocellulose to Ethanol: A Review of Production Process." Advanced Materials Research 280 (July 2011): 246–49. http://dx.doi.org/10.4028/www.scientific.net/amr.280.246.

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Lignocellulose biomass is a kind of rich reserve in china, and it is a renewable bio-resource. Researches on the bioconversion of lignocellulose (lignocellulosic biomass) to ethanol have been hot spot in recent years. The key technologies of producing fuel alcohol by aspects of lignocellulosic raw materials, pretreatment technology, fermentation process, enzymatic hydrolysis and fermentation of strains as well as the removal of fermentation inhibitors have been reviewed. It is pointed out that the improvement of fermentation strains, exploitation of double function saccharomyces cerevisiae (glucose and xylose fermenting) to ethanol, will be the direction and focus in future researches.

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Forsberg, Kevin J., Sanket Patel, Evan Witt, Bin Wang, Tyler D. Ellison, and Gautam Dantas. "Identification of Genes Conferring Tolerance to Lignocellulose-Derived Inhibitors by Functional Selections in Soil Metagenomes." Applied and Environmental Microbiology 82, no. 2 (November 6, 2015): 528–37. http://dx.doi.org/10.1128/aem.02838-15.

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ABSTRACTThe production of fuels or chemicals from lignocellulose currently requires thermochemical pretreatment to release fermentable sugars. These harsh conditions also generate numerous small-molecule inhibitors of microbial growth and fermentation, limiting production. We applied small-insert functional metagenomic selections to discover genes that confer microbial tolerance to these inhibitors, identifying both individual genes and general biological processes associated with tolerance to multiple inhibitory compounds. Having screened over 248 Gb of DNA cloned from 16 diverse soil metagenomes, we describe gain-of-function tolerance against acid, alcohol, and aldehyde inhibitors derived from hemicellulose and lignin, demonstrating that uncultured soil microbial communities hold tremendous genetic potential to address the toxicity of pretreated lignocellulose. We recovered genes previously known to confer tolerance to lignocellulosic inhibitors as well as novel genes that confer tolerance via unknown functions. For instance, we implicated galactose metabolism in overcoming the toxicity of lignin monomers and identified a decarboxylase that confers tolerance to ferulic acid; this enzyme has been shown to catalyze the production of 4-vinyl guaiacol, a valuable precursor to vanillin production. These metagenomic tolerance genes can enable the flexible design of hardy microbial catalysts, customized to withstand inhibitors abundant in specific bioprocessing applications.

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Wang, X., E. N. Miller, L. P. Yomano, X. Zhang, K. T. Shanmugam, and L. O. Ingram. "Increased Furfural Tolerance Due to Overexpression of NADH-Dependent Oxidoreductase FucO in Escherichia coli Strains Engineered for the Production of Ethanol and Lactate." Applied and Environmental Microbiology 77, no. 15 (June 17, 2011): 5132–40. http://dx.doi.org/10.1128/aem.05008-11.

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ABSTRACTFurfural is an important fermentation inhibitor in hemicellulose sugar syrups derived from woody biomass. The metabolism of furfural by NADPH-dependent oxidoreductases, such as YqhD (lowKmfor NADPH), is proposed to inhibit the growth and fermentation of xylose inEscherichia coliby competing with biosynthesis for NADPH. The discovery that the NADH-dependent propanediol oxidoreductase (FucO) can reduce furfural provided a new approach to improve furfural tolerance. Strains that produced ethanol or lactate efficiently as primary products from xylose were developed. These strains included chromosomal mutations inyqhDexpression that permitted the fermentation of xylose broths containing up to 10 mM furfural. Expression offucOfrom plasmids was shown to increase furfural tolerance by 50% and to permit the fermentation of 15 mM furfural. Product yields with 15 mM furfural were equivalent to those of control strains without added furfural (85% to 90% of the theoretical maximum). These two defined genetic traits can be readily transferred to enteric biocatalysts designed to produce other products. A similar strategy that minimizes the depletion of NADPH pools by native detoxification enzymes may be generally useful for other inhibitory compounds in lignocellulosic sugar streams and with other organisms.

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Mishra, Abhishek, Ajay K. Sharma, Sumit Sharma, A. S. Mathur, R. P. Gupta, and D. K. Tuli. "Lignocellulosic bioethanol production employing newly isolated inhibitor and thermotolerant Saccharomyces cerevisiae DBTIOC S24 strain in SSF and SHF." RSC Advances 6, no. 29 (2016): 24381–90. http://dx.doi.org/10.1039/c6ra00007j.

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Semencenko, Valentina, Ljiljana Mojovic, Slobodan Petrovic, and Ozren Ocic. "Recent trends in bioethanol production." Chemical Industry 65, no. 2 (2011): 103–14. http://dx.doi.org/10.2298/hemind100913068s.

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The rapid depletion of the world petroleum supply and the increasing problem of greenhouse gas effects have strenghtened the worldwide interest in alternative, nonpetroleum sources of energy. Bioethanol accounts for the majority of biofuel use worldwide, either as a fuel or a gasoline enhancer. Utilization of bioethanol can significantly reduce petroleum use and exhaust greenhouse gas emission. The production of this fuel is increasing over the years, and has reached the level of 73.9 billion liters during the year 2009. Even though ethanol production for decades mainly depended on energy crops containing starch and sugar (corn, sugar cane etc.), new technologies for converting lignocellulosic biomass into ethanol are under development today. The use of lignocellulosic biomass, such as agricultural residues, forest and municipial waste, for the production of biofuels will be unavoidable if liquid fossil fuels are to be replaced by renewable and sustainable alternatives. For biological conversion of lignocellulosic biomass, pretreatment plays a central role affecting all unit operations in the process and is also an important cost deterrent to the comercial viability of the process. The key obstacles are: pretreatment selection and optimization; decreasing the cost of the enzymatic hydrolysis; maximizing the conversion of sugars (including pentoses) to ethanol; process scale-up and integration to minimize energy and water demand; characterization and evaluation of the lignin co-product; and lastly, the use of the representative and reliable data for cost estimation, and the determination of environmental and socio-economic impacts. Currently, not all pretreatments are capable of producing biomass that can be converted to sugars in high enough yield and concentration, while being economically viable. For the three main types of feedstocks, the developement of effective continuous fermentation technologies with near to 100% yields and elevated volumetric productivities is one of the main research subjects in the ethanol industry. The application of new, engineered enzyme systems for cellulose hydrolysis, the construction of inhibitor tolerant pentose fermenting strains, combined with optimized process integration promise significant improvements.

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Sárvári Horváth, Ilona, Carl Johan Franzén, Mohammad J. Taherzadeh, Claes Niklasson, and Gunnar Lidén. "Effects of Furfural on the Respiratory Metabolism of Saccharomyces cerevisiae in Glucose-Limited Chemostats." Applied and Environmental Microbiology 69, no. 7 (July 2003): 4076–86. http://dx.doi.org/10.1128/aem.69.7.4076-4086.2003.

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ABSTRACT Effects of furfural on the aerobic metabolism of the yeast Saccharomyces cerevisiae were studied by performing chemostat experiments, and the kinetics of furfural conversion was analyzed by performing dynamic experiments. Furfural, an important inhibitor present in lignocellulosic hydrolysates, was shown to have an inhibitory effect on yeast cells growing respiratively which was much greater than the inhibitory effect previously observed for anaerobically growing yeast cells. The residual furfural concentration in the bioreactor was close to zero at all steady states obtained, and it was found that furfural was exclusively converted to furoic acid during respiratory growth. A metabolic flux analysis showed that furfural affected fluxes involved in energy metabolism. There was a 50% increase in the specific respiratory activity at the highest steady-state furfural conversion rate. Higher furfural conversion rates, obtained during pulse additions of furfural, resulted in respirofermentative metabolism, a decrease in the biomass yield, and formation of furfuryl alcohol in addition to furoic acid. Under anaerobic conditions, reduction of furfural partially replaced glycerol formation as a way to regenerate NAD+. At concentrations above the inlet concentration of furfural, which resulted in complete replacement of glycerol formation by furfuryl alcohol production, washout occurred. Similarly, when the maximum rate of oxidative conversion of furfural to furoic acid was exceeded aerobically, washout occurred. Thus, during both aerobic growth and anaerobic growth, the ability to tolerate furfural appears to be directly coupled to the ability to convert furfural to less inhibitory compounds.

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Long, Tingting, Peng Zhang, Jingze Yu, Yushan Gao, Xiaoqin Ran, and Yonghao Li. "Regulation of β-Disaccharide Accumulation by β-Glucosidase Inhibitors to Enhance Cellulase Production in Trichoderma reesei." Fermentation 8, no. 5 (May 17, 2022): 232. http://dx.doi.org/10.3390/fermentation8050232.

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Trichoderma reesei is a high-yield producer of cellulase for applications in lignocellulosic biomass conversion, but its cellulase production requires induction. A mixture of glucose and β-disaccharide has been demonstrated to achieve high-level cellulase production. However, as inducers, β-disaccharides are prone to be hydrolyzed by β-glucosidase (BGL) during fermentation, therefore β-disaccharides need to be supplemented through feeding to overcome this problem. Here, miglitol, an α-glucosidase inhibitor, was investigated as a BGL inhibitor, and exhibited an IC50 value of 2.93 μg/mL. The cellulase titer was more than two-fold when miglitol was added to the fermentation medium of T. reesei. This method was similar to the prokaryotic expression system using unmetabolized isopropyl-β-D-thiogalactopyranoside (IPTG) as the inducer instead of lactose to continuously induce gene expression. However, cellulase activity was not enhanced with BGL inhibition when lactose or cellulose was used as an inducer, which demonstrated that the transglycosidase activity of BGL is important for the inducible activity of lactose and cellulose. This novel method demonstrates potential in stimulating cellulase production and provides a promising system for T. reesei protein expression.

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Baptista, Marlene, Joana T. Cunha, and Lucília Domingues. "Establishment of Kluyveromyces marxianus as a Microbial Cell Factory for Lignocellulosic Processes: Production of High Value Furan Derivatives." Journal of Fungi 7, no. 12 (December 7, 2021): 1047. http://dx.doi.org/10.3390/jof7121047.

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The establishment of lignocellulosic biorefineries is dependent on microorganisms being able to cope with the stressful conditions resulting from the release of inhibitory compounds during biomass processing. The yeast Kluyveromyces marxianus has been explored as an alternative microbial factory due to its thermotolerance and ability to natively metabolize xylose. The lignocellulose-derived inhibitors furfural and 5-hydroxymethylfurfural (HMF) are considered promising building-block platforms that can be converted into a wide variety of high-value derivatives. Here, several K. marxianus strains, isolated from cocoa fermentation, were evaluated for xylose consumption and tolerance towards acetic acid, furfural, and HMF. The potential of this yeast to reduce furfural and HMF at high inhibitory loads was disclosed and characterized. Our results associated HMF reduction with NADPH while furfural-reducing activity was higher with NADH. In addition, furans’ inhibitory effect was higher when combined with xylose consumption. The furan derivatives produced by K. marxianus in different conditions were identified. Furthermore, one selected isolate was efficiently used as a whole-cell biocatalyst to convert furfural and HMF into their derivatives, furfuryl alcohol and 2,5-bis(hydroxymethyl)furan (BHMF), with high yields and productivities. These results validate K. marxianus as a promising microbial platform in lignocellulosic biorefineries.

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Rani, Devitra Saka, and Cut Nanda Sari. "Dilute Acid Pretreatment And Enzymatic Hydrolysis Of Lignocellulosic Biomass For Butanol Production As Biofuel." Scientific Contributions Oil and Gas 35, no. 1 (February 15, 2022): 39–48. http://dx.doi.org/10.29017/scog.35.1.776.

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Biobutanol is one of the promising biofuel for substituting gasoline. Biobutanol produced from biomass fermentation using solventogenic clostridia which are able to convert a wide range of carbon sources to fuels such as butanol. Therefore, lignocellosic biomass has great potential as fermentation substrate for biobutanol production. Lignocellosic biomass should be hydrolized before fermentation by a pretreatment process and enzymatic hydrolysis. The various lignocellulosic biomass pretreatment will infl uence in butanol production depending on fermentable sugars content. The objective of this research is to get potential lignocellulosic biomass using dilute acid pretreatment and enzymatic hydrolysis process for biobutanol production. Eight types of biomass from sugarcane bagasse, rice straw, rice husk, empty fruit bunch (EFB) of palm oil, corn cob, pulp waste, traditional market organic waste, and microalgae were used in this experiment. After hydrolysis, the high result of total fermentable sugars in corn cobs, bagasse, rice straw, and rice husk, shows good opportunity of these biomass to be used as fermentation feedstocks for biobutanol production. In addition, pulp waste, organic waste, and microalgae are prospective as raw material but require more appropriate treatment either for to break down the cellulose/hemicellulose or to enhance reducing sugar content. Fine milling and delignifi cation have no signifi cant effect on cellulosic biomass conversion into fermentable sugars. Therefore, the production cost can be reduced. In order to enhance the sugar content and reduce the formation of inhibitor product, it is necessary to examine dilute acid pretreatment variations and appropriate operating conditions of enzymatic hydrolysis process

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Medina, Víctor Guadalupe, Marinka J. H. Almering, Antonius J. A. van Maris, and Jack T. Pronk. "Elimination of Glycerol Production in Anaerobic Cultures of a Saccharomyces cerevisiae Strain Engineered To Use Acetic Acid as an Electron Acceptor." Applied and Environmental Microbiology 76, no. 1 (November 13, 2009): 190–95. http://dx.doi.org/10.1128/aem.01772-09.

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ABSTRACT In anaerobic cultures of wild-type Saccharomyces cerevisiae, glycerol production is essential to reoxidize NADH produced in biosynthetic processes. Consequently, glycerol is a major by-product during anaerobic production of ethanol by S. cerevisiae, the single largest fermentation process in industrial biotechnology. The present study investigates the possibility of completely eliminating glycerol production by engineering S. cerevisiae such that it can reoxidize NADH by the reduction of acetic acid to ethanol via NADH-dependent reactions. Acetic acid is available at significant amounts in lignocellulosic hydrolysates of agricultural residues. Consistent with earlier studies, deletion of the two genes encoding NAD-dependent glycerol-3-phosphate dehydrogenase (GPD1 and GPD2) led to elimination of glycerol production and an inability to grow anaerobically. However, when the E. coli mhpF gene, encoding the acetylating NAD-dependent acetaldehyde dehydrogenase (EC 1.2.1.10; acetaldehyde + NAD+ + coenzyme A ↔ acetyl coenzyme A + NADH + H+), was expressed in the gpd1Δ gpd2Δ strain, anaerobic growth was restored by supplementation with 2.0 g liter−1 acetic acid. The stoichiometry of acetate consumption and growth was consistent with the complete replacement of glycerol formation by acetate reduction to ethanol as the mechanism for NADH reoxidation. This study provides a proof of principle for the potential of this metabolic engineering strategy to improve ethanol yields, eliminate glycerol production, and partially convert acetate, which is a well-known inhibitor of yeast performance in lignocellulosic hydrolysates, to ethanol. Further research should address the kinetic aspects of acetate reduction and the effect of the elimination of glycerol production on cellular robustness (e.g., osmotolerance).

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Nevoigt, Elke. "Progress in Metabolic Engineering of Saccharomyces cerevisiae." Microbiology and Molecular Biology Reviews 72, no. 3 (September 2008): 379–412. http://dx.doi.org/10.1128/mmbr.00025-07.

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SUMMARY The traditional use of the yeast Saccharomyces cerevisiae in alcoholic fermentation has, over time, resulted in substantial accumulated knowledge concerning genetics, physiology, and biochemistry as well as genetic engineering and fermentation technologies. S. cerevisiae has become a platform organism for developing metabolic engineering strategies, methods, and tools. The current review discusses the relevance of several engineering strategies, such as rational and inverse metabolic engineering, evolutionary engineering, and global transcription machinery engineering, in yeast strain improvement. It also summarizes existing tools for fine-tuning and regulating enzyme activities and thus metabolic pathways. Recent examples of yeast metabolic engineering for food, beverage, and industrial biotechnology (bioethanol and bulk and fine chemicals) follow. S. cerevisiae currently enjoys increasing popularity as a production organism in industrial (“white”) biotechnology due to its inherent tolerance of low pH values and high ethanol and inhibitor concentrations and its ability to grow anaerobically. Attention is paid to utilizing lignocellulosic biomass as a potential substrate.

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Lennartsson, Patrik R., Keikhosro Karimi, Lars Edebo, and Mohammad J. Taherzadeh. "Effects of different growth forms of Mucor indicus on cultivation on dilute-acid lignocellulosic hydrolyzate, inhibitor tolerance, and cell wall composition." Journal of Biotechnology 143, no. 4 (September 2009): 255–61. http://dx.doi.org/10.1016/j.jbiotec.2009.07.011.

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Abdel-Rahman, Mohamed Ali, Saad El-Din Hassan, Hassan M. A. Alrefaey, and Tamer Elsakhawy. "Efficient Co-Utilization of Biomass-Derived Mixed Sugars for Lactic Acid Production by Bacillus coagulans Azu-10." Fermentation 7, no. 1 (February 18, 2021): 28. http://dx.doi.org/10.3390/fermentation7010028.

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Lignocellulosic and algal biomass are promising substrates for lactic acid (LA) production. However, lack of xylose utilization and/or sequential utilization of mixed-sugars (carbon catabolite repression, CCR) from biomass hydrolysates by most microorganisms limits achievable titers, yields, and productivities for economical industry-scale production. This study aimed to design lignocellulose-derived substrates for efficient LA production by a thermophilic, xylose-utilizing, and inhibitor-resistant Bacillus coagulans Azu-10. This strain produced 102.2 g/L of LA from 104 g/L xylose at a yield of 1.0 g/g and productivity of 3.18 g/L/h. The CCR effect and LA production were investigated using different mixtures of glucose (G), cellobiose (C), and/or xylose (X). Strain Azu-10 has efficiently co-utilized GX and CX mixture without CCR; however, total substrate concentration (>75 g/L) was the only limiting factor. The strain completely consumed GX and CX mixture and homoferemnatively produced LA up to 76.9 g/L. On the other hand, fermentation with GC mixture exhibited obvious CCR where both glucose concentration (>25 g/L) and total sugar concentration (>50 g/L) were the limiting factors. A maximum LA production of 50.3 g/L was produced from GC mixture with a yield of 0.93 g/g and productivity of 2.09 g/L/h. Batch fermentation of GCX mixture achieved a maximum LA concentration of 62.7 g/L at LA yield of 0.962 g/g and productivity of 1.3 g/L/h. Fermentation of GX and CX mixture was the best biomass for LA production. Fed-batch fermentation with GX mixture achieved LA production of 83.6 g/L at a yield of 0.895 g/g and productivity of 1.39 g/L/h.

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Chen, Yudian, Nian Peng, Yushan Gao, Qian Li, Zancheng Wang, Bo Yao, and Yonghao Li. "Two-Stage Pretreatment of Jerusalem Artichoke Stalks with Wastewater Recycling and Lignin Recovery for the Biorefinery of Lignocellulosic Biomass." Processes 11, no. 1 (January 1, 2023): 127. http://dx.doi.org/10.3390/pr11010127.

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Jerusalem artichoke (Helianthus tuberosus L.) is emerging as one of the energy plants considered for biofuel production. Alkali and alkali-involved pretreatment methods have been widely used for the bioconversion of cellulosic materials due to their high sugar yield and low inhibitor release. However, the recovery and treatment of wastewater (black liquor) have been poorly studied. Here, we present a novel two-stage pretreatment process design for recycling black liquor. Jerusalem artichoke stalk (JAS) was first treated with 2% (w/v) NaOH, after which lignin was recovered by H2SO4 at pH 2.0 from the black liquor. The recycled solutions were subsequently used to treat the NaOH-pretreated JAS for the second time to dissolve hemicellulose. CO-pretreated JAS, hydrolysates, and acid-insoluble lignin were obtained after the above-mentioned two-stage pretreatment. A reducing sugar yield of 809.98 mg/g Co-pretreated JAS was achieved after 48 h at 5% substrate concentration using a cellulase dosage of 25 FPU/g substrate. In addition, hydrolysates containing xylose and acid-insoluble lignin were obtained as byproducts. The pretreatment strategy described here using alkali and acid combined with wastewater recycling provides an alternative approach for cellulosic biorefinery.

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Madadi, Meysam, Yuanyuan Tu, and Aqleem Abbas. "Pretreatment of Lignocelollusic Biomass Based on Improving Enzymatic Hydrolysis." International Journal of Applied Sciences and Biotechnology 5, no. 1 (March 25, 2017): 1–11. http://dx.doi.org/10.3126/ijasbt.v5i1.17018.

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Lignocellulosic materials among the alternative energy resources are the most desirable resources that can be employed to produce cellulosic ethanol, but this materials due to physical and chemical structure arranges strong native recalcitrance and results in low yield of ethanol. Then, a proper pre-treatment method is required to overcome this challenge. Until now, different pre-treatment technologies have been established to enhance lignocellulosic digestibility. This paper widely describes the structure of lignocellulosic biomass and effective parameters in pre-treatment of lignocelluloses, such as cellulose crystallinity, accessible surface area, and protection by lignin and hemicellulose. In addition, an overview about the most important pre-treatment processes include physical, chemical, and biological are provided. Finally, we described about the inhibitors enzymes which produced from sugar degradation during pre-treatment process and the ways to control this inhibitors.Int. J. Appl. Sci. Biotechnol. Vol 5(1): 1-11

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Ledingham, Edward T., Kieran P. Stockton, and Ben W. Greatrex. "Efficient Synthesis of an Indinavir Precursor from Biomass-Derived (–)-Levoglucosenone." Australian Journal of Chemistry 70, no. 10 (2017): 1146. http://dx.doi.org/10.1071/ch17227.

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Lignocellulosic biomass pyrolysis with acid catalysis selectively produces the useful chiral synthon 6,8-dioxabicyclo[3.2.1]oct-2-ene-4-one ((–)-levoglucosenone, LGO). In this report, LGO was used to prepare (3R,5S)-3-benzyl-5-(hydroxymethyl)-4,5-dihydrofuran-2(3H)-one, which is an intermediate used in the construction of antivirals including the protease inhibitor indinavir. To achieve the synthesis, the hydrogenated derivative of LGO was functionalised using aldol chemistry and various aromatic aldehydes were used to show the scope of the reaction. Choice of base affected reaction times and the best yields were obtained using 1,1,3,3-tetramethylguanidine. Hydrogenation of the α-benzylidene-substituted bicyclic system afforded a 4 : 3 equatorial/axial mixture of isomers, which was equilibrated to a 97 : 3 mixture under basic conditions. Subsequent Baeyer–Villiger reaction afforded the target lactone in 57 % overall yield for four steps, a route that avoids the protection and strong base required in the traditional approach. The aldol route is contrasted with the α-alkylation and a Baylis–Hillman approach that also both start with LGO.

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van der Maas, Lucas, Jasper L. S. P. Driessen, and Solange I. Mussatto. "Effects of Inhibitory Compounds Present in Lignocellulosic Biomass Hydrolysates on the Growth of Bacillus subtilis." Energies 14, no. 24 (December 14, 2021): 8419. http://dx.doi.org/10.3390/en14248419.

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This study evaluated the individual and combined effects of inhibitory compounds formed during pretreatment of lignocellulosic biomass on the growth of Bacillus subtilis. Ten inhibitory compounds commonly present in lignocellulosic hydrolysates were evaluated, which included sugar degradation products (furfural and 5-hydroxymethylfurfural), acetic acid, and seven phenolic compounds derived from lignin (benzoic acid, vanillin, vanillic acid, ferulic acid, p-coumaric acid, 4-hydroxybenzoic acid, and syringaldehyde). For the individual inhibitors, syringaldehyde showed the most toxic effect, completely inhibiting the strain growth at 0.1 g/L. In the sequence, assays using mixtures of the inhibitory compounds at a concentration of 12.5% of their IC50 value were performed to evaluate the combined effect of the inhibitors on the strain growth. These experiments were planned according to a Plackett–Burman experimental design. Statistical analysis of the results revealed that in a mixture, benzoic acid and furfural were the most potent inhibitors affecting the growth of B. subtilis. These results contribute to a better understanding of the individual and combined effects of inhibitory compounds present in biomass hydrolysates on the microbial performance of B. subtilis. Such knowledge is important to advance the development of sustainable biomanufacturing processes using this strain cultivated in complex media produced from lignocellulosic biomass, supporting the development of efficient bio-based processes using B. subtilis.

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Zhang, Dongyan, Yuyang Fan, Anqing Zheng, Zengli Zhao, Fengyun Wang, and Haibin Li. "Maximizing Anhydrosugar Production from Fast Pyrolysis of Eucalyptus Using Sulfuric Acid as an Ash Catalyst Inhibitor." Catalysts 8, no. 12 (December 3, 2018): 609. http://dx.doi.org/10.3390/catal8120609.

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Anhydrosugars, such as levoglucosan (LG), are high value-added chemicals which are mainly derived from fast pyrolysis of pure cellulose. However, fast pyrolysis of raw lignocellulosic biomass usually produces a very low amount of levoglucosan, since alkali and alkaline earth metals (AAEM) present in the ash can serve as the catalysts to inhibit the formation of levoglucosan through accelerating the pyranose ring-opening reactions. In this study, eucalyptus was impregnated with H2SO4 solutions with varying concentrations (0.25–1.25%). The characteristics of ash derived from raw and H2SO4-impregnated eucalyptus were characterized by X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD). The pyrolysis behaviors of raw and H2SO4-impregnated eucalyptus were performed on the thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TG analysis demonstrated that the H2SO4-impregnated eucalyptus produced less char than raw eucalyptus. Py-GC/MS analysis showed that even small amounts of H2SO4 can obviously improve the production of anhydrosugars and phenols and suppressed the formation of carboxylic acids, aldehydes, and ketones from fast pyrolysis of eucalyptus. The rank order of levoglucosan yield from raw and impregnated eucalyptus was raw < 1.25% H2SO4 < 1% H2SO4 < 0.75% H2SO4 < 0.25% H2SO4 < 0.5% H2SO4. The maximum yield of levoglucosan (21.3%) was obtained by fast pyrolysis of eucalyptus impregnated with 0.5% H2SO4, which was close to its theoretical yield based on the cellulose content. The results could be ascribed to that H2SO4 can react with AAEM (e.g., Na, K, Ca, and Mg) and lignin to form lignosulfonate, thus acting as an inhibitor to suppress the catalytic effects of AAEM during fast pyrolysis of eucalyptus.

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Bian, Huiyang, Xinxing Wu, Jing Luo, Yongzhen Qiao, Guigan Fang, and Hongqi Dai. "Valorization of Alkaline Peroxide Mechanical Pulp by Metal Chloride-Assisted Hydrotropic Pretreatment for Enzymatic Saccharification and Cellulose Nanofibrillation." Polymers 11, no. 2 (February 14, 2019): 331. http://dx.doi.org/10.3390/polym11020331.

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Developing economical and sustainable fractionation technology of lignocellulose cell walls is the key to reaping the full benefits of lignocellulosic biomass. This study evaluated the potential of metal chloride-assisted p-toluenesulfonic acid (p-TsOH) hydrolysis at low temperatures and under acid concentration for the co-production of sugars and lignocellulosic nanofibrils (LCNF). The results indicated that three metal chlorides obviously facilitated lignin solubilization, thereby enhancing the enzymatic hydrolysis efficiency and subsequent cellulose nanofibrillation. The CuCl2-assisted hydrotropic pretreatment was most suitable for delignification, resulting in a relatively higher enzymatic hydrolysis efficiency of 53.2%. It was observed that the higher residual lignin absorbed on the fiber surface, which exerted inhibitory effects on the enzymatic hydrolysis, while the lower lignin content substrates resulted in less entangled LCNF with thinner diameters. The metal chloride-assisted rapid and low-temperature fractionation process has a significant potential in achieving the energy-efficient and cost-effective valorization of lignocellulosic biomass.

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Journal articles on the topic 'Lignocellulosic inhibitor'

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