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Autor: Grafiati
Data publikacji: 4 czerwca 2021
Data aktualizacji: 7 lipca 2024

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1

Pereira, Daniel Albuquerque. "Quorum sensing em cianobactérias". Universidade Federal de Minas Gerais, 2014. http://hdl.handle.net/1843/BUOS-9NFKZN.

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The terminology quorum sensing is used to identify a cellular communication phenomenon in the bacterial domain, which happens when a bacteria population reaches a defined cellular density. During the activation of the phenomenon changes in the expression of several genes and consequently in the physiology of the cell are triggered. Concerning cyanobacteria, there is a lack of information about quorum sensing. Some studies show that quorum sensing inducer compounds may alter physiological characteristics of certain cyanobacteria strains. Besides that, indirect evidences have shown that cellular density may influence microcystin production. The capacity to form blooms in certain conditions is also an important characteristic found in the cyanobacteria group. In these conditions the cellular density of a population may reach elevated numbers, consisting of an ideal scenario for quorum sensing. There are a remarkably number of studies regarding cyanobacterial blooms, but little is known about what happens with a population at molecular and physiological levels. The aim of this study was to characterize four strains of cyanobacteria regarding the production of peptides and to use these strains in experiments with the objective of investigating evidences of quorum sensing system in cyanobacteria and its connection with the synthesis of oligopeptides. In order to fulfill these objectives biochemical and molecular techniques were used. The results obtained showed that the production of oligopeptides is affected by cellular density, being, in most cases, higher in situations with an elevated number of cells. It was demonstrated by real time PCR that acylhomoserine lactone autoinducers (AHLs), which are responsible for the activation of the quorum sensing in various groups of gram-negative bacteria, affect the transcription of genes linked to the production of microcystins, cyanopeptolins and microviridins. Through ELISA assays it was also seen that AHLs affect the microcystin production in the same pattern in which they affect the transcription of genes connected to its synthesis. With this work it was observed that cellular density and possibly quorum sensing are key factors in secondary metabolite synthesis in cyanobacteria and should be considered when studying these compounds and their connection with the environment.
O termo quorum sensing refere-se a um fenômeno de comunicação celular existente em bactérias, onde ao se atingir uma certa densidade populacional mudanças no padrão de expressão gênica, e consequentemente da fisiologia das células são disparadas. No que diz respeito a cianobactérias, poucos trabalhos com enfoque em quorum sensing foram realizados. Alguns estudos mostram que substâncias indutoras de quorum sensing podem alterar algumas características fisiológicas de algumas cepas de cianobactérias. Evidências indiretas mostraram que a diferença na densidade celular pode afetar a produção de microcistinas. A capacidade de produzir florações em determinadas condições é outro aspecto importante das cianobactérias. Nestas situações a densidade populacional das espécies dominantes atinge valores muito altos, podendo constituir uma situação ideal para a ocorrência do quorum sensing. Existem diversos estudos sobre florações, no entanto pouco se sabe sobre o que ocorre com as populações de cianobactérias em nivel molecular e também fisiológico. Este trabalho teve o objetivo de caracterizar quatro cepas de cianobactérias quanto à produção de peptídeos e utilizá-las em experimentos com a finalidade de encontrar evidências da existência de quorum sensing em cianobactérias e sua relação com a produção de oligopeptídeos. Para cumprir estes objetivos foram utilizadas técnicas de bioquímica e biologia molecular. Os resultados encontrados demonstraram que a produção de oligopeptídeos é afetada pela densidade celular, sendo, na maioria dos casos, maior nas situações com alto número de células. Foi verificado através de PCR em tempo real que auto indutores do tipo acil-homoserina lactonas (AHLs), responsáveis pela ativação do quorum sensing em diversos grupos de bactérias gram-negativas, afetam a transcrição de genes ligados a produção dos peptídeos microcistina, cianopeptolina e microviridina. Através de testes de ELISA foi visto também que as AHLs afetam a produção de microcistinas da mesma forma que influenciam a transcrição dos genes liagados à sua síntese. Com este trabalho foi visto que densidade celular e, possivelmente, quorum sensing são fatores importantes na síntese de metabólitos secundários em cinobactérias, que devem ser levados em consideração ao se estudar estes compostos e suas relações com o ambiente.
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2

Teplitski, Max I. "Quorum sensing in Sinorhizobium meliloti and effect of plant signals on bacterial quorum sensing". The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1029777185.

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3

Teplitski, Maxim Igorevich. "Quorum sensing in Sinorhizobium meliloti and effect of plant signals on bacterial quorum sensing /". The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486463803600062.

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4

Teplitski, Maxim I. "Quorum sensing in Sinorhizobium meliloti and effect of plant signals on bacterial quorum sensing". Columbus, Ohio : Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1029777185.

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Thesis (Ph. D.)--Ohio State University, 2002.
Title from first page of PDF file. Document formatted into pages; contains xi, 148 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Wolfgang D. Bauer, Dept. of Horticulture and Crop Science. Includes bibliographical references (p. 127-148).
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5

Weber, Marc. "Stochastic Effects in Quorum Sensing". Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/276154.

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Stochastic fluctuations, or noise, are ubiquitous in biological systems and play an important role in many cellular processes. Experimental evidences have shown that noise affects the reliability of cell coordination in populations of communicating cells. In this thesis, we study the effects of stochasticity in the emergence of collective behavior in populations of bacteria communicating by QS. We focus on the genetic switch as a paradigm of cellular decision making in both natural and synthetic bacterial systems. Our approach is based on mathematical modeling and stochastic simulations, both at the level of the single cell and at the level of the cell population. We focus on four main topics. In the first topic, we analyze the interplay between intracellular noise and the diffusion process of the QS signaling mechanism. We build a model describing the expression of the signaling molecule and its diffusion in a population of cells, focusing on the situation of very low constitutive expression rate. We show that varying the diffusion rate produces a repertoire of dynamics for the signaling molecule. Our results reveal the contribution of intrinsic noise and transcriptional noise (mRNA copy number fluctuations) in the fluctuations of the signaling molecule. We observe that the total noise exhibits a maximum as a function of the diffusion rate, in contrast to previous studies. Thus, the QS communication mechanism modifies the fluctuations of the signaling molecule inside the cell and interacts with the gene expression noise. In the second topic, we study the effects of gene expression noise on the precision of the population coordination in the QS activation of the LuxR/LuxI system. We analyze the response and dynamics of a population of cells to different levels of autoinducer. Our results show that gene expression noise in LuxR is the main factor that controls the transient variability of the QS activation. This study sheds light on the relation between the single cell stochastic dynamics and the collective behavior in a population of communicating cells. In the third topic, we analyze the effects of intrinsic noise in an autoactivating switch in an isolated single cell. We show that noise promotes the stability of the low-state phenotype of the switch and that the bistable region is extended when increasing the intensity of the fluctuations, an effect that we call stochastic stabilization. Our results show that intrinsic noise modifies the epigenetic landscape as well as the switching rate, which results in complex behavior of the stochastic switching dynamics when varying the intensity of noise. Thus, at the level of a single cell, intrinsic noise contributes to the cell-to-cell variability of the genetic switch and can modify its stable states and its dynamics. In the fourth topic, we build a model of a population of toggle switches communicating by the exchange of two diffusible QS signals. We show that increasing the diffusion rate, which increases the coupling strength between the cells, leads to a phase transition from an unordered phase where the cells randomly flip between the two states of the switch, to an ordered phase with all the cells locked into the same stable state. The same transition is found in a population of cells growing exponentially in a closed volume. Moreover, the response of the cells to a varying external signal exhibits a hysteresis loop. We show that the cell-cell coupling enhances the sensitivity of the population response to the external signal and suggest that this new mechanism could be used to increase the robustness and sensitivity of biosensors. Our results suggest a new mechanism for collective cell decision making based on the phenomenon of phase transition.
En aquesta tesi, estudiem els efectes de la estocàsticitat en la aparició del comportament col·lectiu en poblacions de bacteris que comuniquen per quorum sensing (QS). Ens centrem en el interruptor genètic com a paradigma dels processos de decisió cel·lulars tant en sistemes de bacteris naturals com sintètics. El nostre mètode es basa en la modelització matemàtica i en les simulacions estocàstiques, tant a nivell d'una cèl·lula individual com a nivell d'una població de cèl·lules. A nivell d'una cèl·lula individual, mostrem que el soroll afavoreix l'estabilitat del fenotip de l'estat ``baix'' de l'interruptor genètic autoactivador i que la regió de biestabilitat s'estén quan creix la intensitat de les fluctuacions, un efecte que hem anomenat estabilització estocàstica. A nivell d'una població de cèl·lules, mostrem que el procés de difusió del mecanisme de QS modifica les fluctuacions i la dinàmica de la molècula autoinductora dins de la cèl·lula i interactua amb el soroll en la expressió genètica. En el sistema canònic de QS LuxR/LuxI, mostrem que el soroll en la expressió genètica de LuxR és el principal factor que controla la variabilitat transitòria de l'activació del QS. El soroll intrínsec disminueix la precisió de la coordinació de la població i modifica la dinàmica de la transició de QS. A més, presentem un model d'una població d'interruptors genètics de toggle switch que comuniquen per l'intercanvi de dos senyals difusius de QS. Mostrem que l'increment de la velocitat de difusió, que augmenta la força de l'acoblament entre les cèl·lules, porta a una transició de fase: va des d'una fase desordenada on les cèl·lules salten de manera aleatòria entre els dos estats de l'interruptor, fins a una fase ordenada amb totes les cèl·lules bloquejades en el mateix estat estable. La mateixa transició s'ha trobat en una població de cèl·lules que creixen exponencialment en un volum tancat, amb totes les cèl·lules entrant en l'estat ordenat quan arriben a una mida crítica del sistema. Els nostres resultats suggereixen un nou mecanisme per la decisió cel·lular col·lectiva basat en el fenomen de la transició de fase.
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6

Lewenza, William Shawn. "Quorum sensing in Burkholderia cepacia". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0017/NQ54796.pdf.

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Isherwood, Karen Elizabeth. "Quorum sensing in Yersinia pestis". Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364667.

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Atkinson, Steven. "Quorum sensing in Yersinia pseudotuberculosis". Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287185.

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Hardman, Andrea M. "Quorum sensing in vibrio anguillarum". Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363936.

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10

Buckley, Catherine M. F. "Quorum sensing in Yersinia pseudotuberculosis". Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273108.

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Chalker, Victoria J. "Quorum sensing in Vibrio anguillarum". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325714.

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Sung, Julia Mei Li. "Quorum sensing in Staphylococcus intermedius". Thesis, Royal Veterinary College (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420706.

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Christie, Joseph Martin. "The search for quorum sensing inhibitors". Thesis, University of Ulster, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529557.

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Nieto, Penalver Carlos Gabriel. "Quorum sensing chez Methylobacterium extorquens AM1". Toulouse 3, 2006. http://www.theses.fr/2006TOU30082.

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Le quorum sensing est un mécanisme de régulation physiologique des bactéries en réponse à des fluctuations de densité de population. Ce projet vise à déterminer si le quorum sensing existe chez la bactérie méthylotrophe facultative et à caractériser ce système. Il est établi que M. Extorquens AM1 possède un système de quorum sensing hiérarchisé. L'enzyme MlaI catalyse la synthèse des molécules signal C14:1-HSL et C14:2-HSL. MsaI, une seconde enzyme, catalyse la synthèse des C8-HSL et C6-HSL. MsaI est impliquée dans le contrôle positif de l'expression de mlaI et la production concomitante des C14:1-HSL et C14:2-HSL. Il a été Methylobacterium extorquens AM1 démontré que tslI, qui code un membre éloigné des enzymes LuxI, exerce un niveau de contrôle supérieur. Les exopolysaccharides sont contrôlées par le quorum sensing chez M. Extorquens AM1. Bien que non essentiel, le quorum sensing confère un avantage pour la colonisation de la plante Arabidopsis thaliana en condition de compétition
Quorum sensing is a regulatory mechanism of the bacterial physiology in response to fluctuations in the population density. The aim of this project was to determine whether the quorum sensing exists in the facultative methylotrophic Methylobacterium extorquens AM1 and to characterize this regulatory system. It was shown that M. Extorquens AM1 possesses a quorum sensing system arranged in a hierarchical manner. The enzyme MlaI catalyzes the synthesis of C14:1-HSL and C14:2-HSL. The enzyme MsaI is responsible for the production of C8-HSL and C6-HSL. MsaI is involved in the expression of mlaI, and the concomitant production of C14:1-HSL and C14:2-HSL. A superior layer of control is exerted by tslI that codes a distant member of the LuxI family. The concentration of extrapolysaccharides is controlled by quorum sensing in M. Extorquens AM1. Although not essential, quorum sensing confers an advantage for the colonization of the model plant Arabidopsis thaliana under competitive conditions
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15

Montagut, Cañete Enrique José. "Immunochemical diagnostic strategies based on Quorum Sensing". Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/670762.

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The final goal of the thesis was to improve the diagnostic of infections caused by P. aeruginosa and S. aureus through a better understanding of the bacterial communication process known as Quorum Sensing (QS) and its implication on the pathogenesis. Subsequently, this objective was based on the development of immunochemical methods to profile the expression of different QS signalling molecules, as tools to investigate the mechanisms involved in the pathogenesis of S. aureus and P. aeruginosa and also to assess the potential role of these molecules as biomarkers of infection. In this thesis, it was synthetized, for the first time, haptens against non-immunogenic molecules from the pqs system of P. aeruginosa (2-heptyl-4-quinolone (HHQ), 2-heptyl-3-hydroxy-(1H)-4- quinolone (PQS) and 2-heptyl-4-hydroxyquinoline N-oxide (HQNO)). Regarding S. aureus, two different hapten synthesis strategies using AIP-IV as a model for other AIPs were explored based on the stability of the native molecule: one of the haptens (AIP4S) contained the original thiolactone cycle found in AIP-IV, yet it was suspected to caused stability problems during the subsequent immunization process, and the other hapten (AIP4NH) was a heterologous structure forming a lactam cycle, more stable versus hydrolysis. By means of bio-conjugation techniques all the haptens were covalently linked to highly immunogenic proteins with excellent yields. Specific polyclonal antibodies were obtained against the aforementioned QS molecules. In the case of S. aureus, the preliminary experiments using the As produced against AIP4S demonstrated higher avidity versus AIP-IV than the one produced against AIP4NH and thus, they were selected for developing the definitive immunochemical assay. Consequently, the preferred strategy for the generation of antibodies against the rest of AIPs (I to III) was the one including the original thiolactone ring. The obtained As were used to develop competitive indirect ELISAs for the quantification of the previously mentioned QS molecules. The detectability achieved in all cases was in the low-nM range, which is under the range of concentrations found in bacterial cultures. In the case of the HHQ, PQS and HQNO assays from P. aeruginosa, the detectability achieved is on the same range that the ones found in clinical samples such as sputum, allowing to continue in the near future their evaluation as biomarkers of infection in such type of clinical samples. Despite the structural similarities between the three quinolone metabolites, the generated antibodies demonstrated greater affinity versus their respective targets, which will allow to differentiate between them in biological samples where the three might be present. In the case of S. aureus, the antibodies raised against AIP4S-HCH also showed greater specificity versus AIP-IV than for any other AIP produced by this pathogen, even though the difference between AIP-I and IV was just one amino acid. As a pilot study on the evaluation of the QS molecules as biomarkers of infection, the developed ELISAs were implemented for the measurement of the mentioned QS molecules in culture broth samples from clinical isolates with different infection types and/or severity. In the case of P. aeruginosa, the assays allowed to stratify patients with distinct severity of infection (acute/chronic) relying on the amount of all three measured quinolones produced by the clinical isolates at 8h of growth. It is noteworthy that these molecules have different biological roles at signalling or physiological level and their concentration in clinical samples might be relevant for understanding the pathogenesis of a P. aeruginosa. Regarding S. aureus, the assay was able to measure AIP-IV produced by agr-IV type strains and different production profiles were observed, nonetheless a higher number of clinical isolates would have to be measured in order to obtain adequate conclusions.
El objetivo final de la tesis fue mejorar el diagnóstico de infecciones causadas por P. aeruginosa y S. aureus mediante una mejor comprensión del proceso de comunicación bacteriana conocido como Quorum Sensing (QS) y su implicación en la patogénesis. Para ello, este objetivo se basó en el desarrollo de métodos inmunoquímicos para evaluar la expresión de diferentes moléculas de señalización QS, como herramientas para investigar los mecanismos implicados en la patogénesis de S. aureus y P. aeruginosa. Del mismo modo, se evaluó en estudios piloto el papel potencial de estas moléculas como biomarcadores de infección. La tesis se dividió en dos apartados principales: herramientas inmunoquímicas para la determinación de moléculas de P. aeruginosa QS como biomarcadores de infección y, por otro lado, herramientas inmunoquímicas para la evaluación de moléculas del QS de S. aureus. Estas secciones están precedidas de capítulos introductorios basados en una revisión bibliográfica sobre el sistema de QS y su detección en ambos patógenos. En los capítulos experimentales se explica: Primero, el diseño y síntesis de haptenos para las moléculas, no inmunogénicas, del QS producidas por P. aeruginosa (2-heptil-4-quinolona (HHQ), 2-heptil-3-hidroxi-(1H)-4-quinolona (PQS) y 2-heptil-4-hidroxiquinolina N-óxido (HQNO)) y S. aureus (AIP-I a IV). En segundo lugar, la síntesis y generación de bioconjugados de anticuerpos policlonales específicos contra las moléculas QS de las dos bacterias patógenas antes mencionadas. En tercer lugar, el desarrollo de herramientas de análisis inmunoquímico para la cuantificación de estas moléculas de QS bacterianas. Posteriormente, se realizaron estudios preliminares sobre el valor potencial de moléculas QS seleccionadas como biomarcadores de infección utilizando las herramientas de análisis inmunoquímico desarrolladas.
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Hasegawa, Hiroaki. "Quorum sensing in soft-rotting Erwinia carotovora". Diss., Columbia, Mo. : University of Missouri-Columbia, 2005. http://hdl.handle.net/10355/5815.

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Thesis (Ph. D.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 22, 2006) Vita. Includes bibliographical references.
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Kotte, Ann-Katherine. "RNPP-type quorum sensing in Clostridium acetobutylicum". Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606841.

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Clostridium acetobutylicum is a Gram-type positive, strictly fennentative, endospore-forming bacterium. It gains energy by converting sugars into organic acids during the first part of its life cycle and into solvents during the second part. This work investigated whether RNPP-type quorum sensing is involved in the regulation of key features such as solventogenesis and sporulation. It identified eight putative RNPP-type Quorum ,S,ensing ,S,ystems (qssA to qssH) in the genome of C. acetobutylicul11, each consisting of a putative Quorum ,S,ensing Regulator (qsr) and Quorum ,S,ensing E.eptide (qsp). ClosTron inactivation of six regulators negatively affected solventogenesis, morphological development or sporulation, whereas inactivation of qsrB had a positive effect. Synthetic QspB-derived pep tides could relieve the repression of solvent formation in a qsrB-overexpressing strain, suggesting that QsrB and QspB fonn a functional quorum sensing system. Two orphan Qsr-type regulators, qsrl and qsrJ, were identified. These regulators are encoded without qsp homologues in a gene cluster that is conserved among the genus Clostridium sensu stricto with qsrl preceding qsrJ. qsrl and qsrJ knockout mutants resembled spoOA mutants as total solvent formation was reduced to below 15 mM and sporulation or granulose accumulation did not occur. The phenotypic changes were con finned at transcriptional level by an RNA-Seq analysis, which also revealed that over 600 genes were significantly differentially regulated, including genes encoding secreted proteins and the Agr-type quorum sensing system. Co-culture and cross streak experiments provided further evidence that QsrI controls the Agrtype and possibly other quorum sensing systems. Key outcomes of this work are the evidence that RNPP-type quorum sensing extends to anaerobic FiJ'micutes and that solvent formation in a Clostridium sp. is controlled by quorum sensing. The discovery of the regulators QrsI and QsrJ was of major importance, showing that other master regulators ex ist beside SpoOA.
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Harty, Christopher. "Bacterial quorum sensing molecules as immune modulators". Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422737.

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Lynch, Martin J. "Quorum sensing in Aeromonas hydrophila biofilm formation". Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324695.

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Wilson, Michael P. "Protein secretion and quorum sensing in Salmonella". Thesis, University of Newcastle Upon Tyne, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275515.

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Muharram, Siti Hanna. "Antagonism of quorum sensing in Staphylococcus aureus". Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438365.

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Paiva, Franciely Paula Toniolo de. "Quorum sensing em Escherichia coli enteropatogênica atípica". Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/87/87131/tde-23032011-172812/.

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Escherichia coli enteropatogênica atípica (aEPEC) faz parte de um grupo de patógenos capazes de formar um tipo de lesão característica em cultura de tecidos epiteliais, denominada attaching and effacing (A/E). Os genes que são necessários para produção da lesão A/E estão localizados em uma ilha de patogenicidade denominada região LEE (locus of enterocyte effacement). A transcrição de genes da região LEE está sujeita a regulação por vários fatores, entre eles quorum sensing, termo utilizado para designar um mecanismo de regulação gênica dependente da concentração celular. Esse mecanismo é usado por bactérias Gram-positivas e Gram-negativas e em ambos os casos envolve a produção e detecção de moléculas sinalizadoras extracelulares, denominadas autoindutores. Até o momento, pelo menos quatro sistemas de quorum sensing foram descritos, entre eles o sistema de autoindutor AI-3 encontrado em bactérias Gram-positivas e Gram-negativas. Diversos mecanismos celulares, entre eles a expressão de fatores de virulência em amostras de EPEC e EHEC, são regulados por esse fenômeno. O principal objetivo deste estudo foi verificar se existe uma possível regulação por quorum sensing na interação in vitro de uma amostra de E. coli da microbiota intestinal com amostras de aEPEC. Após a confirmação da produção de AI-3 por amostras de E.coli da microbiota intestinal foram realizados ensaios de adesão e quantificação utilizando meio pré-condicionado com esta amostra, epinefrina e bloqueadores que confirmaram que os padrões de adesão de aEPEC obtidos em menor tempo são devidos a presença de AI-3 no meio pré-condicionado, indicando a participação de quorum sensing nessa interação. Além disso, foi observado um fenômeno citotóxico nas células que não é produzido pelo AI-3.
Atypical Enteropathogenic Escherichia coli (aEPEC) are part of a group of pathogens capable of forming a type of lesion characteristic of epithelial tissues in culture, called attaching and effacing (A/E). The genes that are required for production of A/E lesion are located in a pathogenicity island called LEE region (locus of enterocyte effacement). The transcription of LEE genes in the region is subject to regulation by various factors, including quorum sensing, a term used to describe a mechanism of gene regulation dependent on cell concentration. This mechanism is used by Gram-positive and Gram-negative and in both cases involves the production and detection of extracellular signaling molecules, called autoinducers. So far, four systems of quorum sensing have been described, including the system of autoinducers AI-3 found in Gram-positive and Gram-negative bacteria. Several cellular mechanisms, including expression of virulence factors in EPEC and EHEC are regulated by this phenomenon. The main objective of this study was to determine whether there is a possible regulation by quorum sensing in the in vitro interaction of a strains of E. coli of the intestinal microbiota with strains aEPEC. After confirming the production of AI-3 in E. coli of the intestinal microbiota were performed adhesion assays and quantification using means preconditioned with this strains, epinephrine, and blockers who confirmed that patterns of adherence of aEPEC obtained in less time are due to the presence of AI-3 in the preconditioned means, indicating the involvement of quorum sensing in this interaction. Furthermore, we observed a phenomenon that cytotoxic cells is not produced by AI-3.
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23

Mamani, Flores Sigde Karina. "Régulation par le quorum sensing chez la bactérie biolixiviante Acidithiobacillus ferrooxidans". Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4117.

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Le Quorum sensing (QS) est un système de communication bactérienne capable de réguler divers processus cellulaires qui dépendent de la densité de la population microbienne. Chez les bactéries à Gram négatif, cela se produit par production de molécules de signalisation auto-inductrices (AI), les acyl homosérine lactones (AHL). La libération d´AHL à l'extérieur de la cellule est détectée par la population bactérienne provoquant en réponse la régulation de l'expression de certains gènes (régulon QS).Notre laboratoire a étudié et identifié un système QS fonctionnel dans la souche Acidithiobacillus ferrooxidans ATCC 23270T. En outre, nous avons montré que des analogues synthétiques d´AHL modulent l´adhésion d´At. ferrooxidansT sur un substrat minéral, tels des coupons de soufre.Dans ce projet de recherche, nous nous proposons d'identifier les gènes qui sont régulés par le QS chez At. ferrooxidansT, en particulier ceux impliqués dans la biogénèse du biofilm. Notre hypothèse est que des analogues synthétiques d’AHL induisent le système QS. Ainsi, nous nous proposons de moduler l´adhésion sur substrat minéral grâce à l'utilisation de ces molécules. L'utilisation de ces AHL permettra de caractériser le régulon QS dans cette souche bactérienne.L'identification d'analogues synthétiques d´AHL qui favorisent l'adhésion à des coupons de soufre nous a permis d'étudier le transcriptome d´At. ferrooxidansT dans des conditions où le régulon QS est stimulé. Puces à ADN d´At. ferrooxidansT avec/sans ces analogues synthétique d´AHLs nous a permis de caractériser le régulon QS et les gènes impliqués dans la biogénèse du biofilm dans les conditions utilisées
Quorum sensing (QS) is a bacterial communication system capable of controlling several cellular processes dependent on the density of the microbial population. In Gram-negative bacteria, it occurs mainly through the production by bacteria of small diffusible signaling molecules, termed autoinducers (AI), of the acyl homoserine lactones type (AHLs). The release of AHLs outside the cell is detected by the bacterial population generating the regulation of the expression of several genes (regulon QS).Our laboratory has studied and identified a functional QS system in the Acidithiobacillus ferrooxidans ATCC 23270T type strain. Besides, by using synthetic analogs of AHLs, we have shown that AHL-type QS molecule analogs modulate adhesion of At. ferrooxidansT to minerals, such as sulfur coupons. In this research, we propose to identify the genes that are regulated by QS in At. ferrooxidansT, particularly those that are associated with biofilm formation. For this, we propose to modulate the adhesion of At. ferrooxidansT to mineral substrate through the use of a synthetic AHL analog. Our working hypothesis postulates that AHLs molecules induce the QS system, and that their use will allow the characterization of the QS regulon of this bacterial strain by transcriptomic analysis.The identification of synthetic AHLs improving adherence of At. ferrooxidansT on sulfur coupons allowed us to study the transcriptome of this organism in conditions in which QS regulon is stimulated. DNA microarrays of At. ferrooxidansT with/without one of these AHLs synthetic analogues allowed us to identify the QS regulon and to determine genes involved in biofilm formation
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24

De, Vizio Daniela. "Investigation of quorum sensing process in Bacillus licheniformis". Thesis, University of Westminster, 2011. https://westminsterresearch.westminster.ac.uk/item/8zxw2/investigation-of-quorum-sensing-process-in-bacillus-licheniformis.

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Quorum sensing is a well-established system of communication adopted by a number of bacterial, and some fungal, populations. This cell density dependent phenomenon is based on the accumulation of small diffusible molecules, termed as quorum sensing molecules, in the extracellular milieu until a threshold concentration triggers alteration in the expression of specific genes culminating in variety of responses including virulence, bioluminescence, sporulation, biofilm formation and secondary metabolites production. In Bacilli, quorum sensing is mediated by small peptides that control competence, sporulation, and the production of certain secondary metabolites in a cell density dependent fashion. Two divergent pathways, triggered by the ComX pheromone and the Competence and Sporulation Factor (CSF), are engaged in the control of these processes. B. licheniformis NCIMB 8874 is a bacterium with industrial relevance for the production of the antimicrobial agent bacitracin. This organism is genetically related to Bacillus subtilis, whose quorum sensing is regulated by the comQXPA operon. This study aimed to investigate the role of the comQXPA locus in B. licheniformis NCIMB 8874 and the production of potential signalling molecules in this bacterium. Production of signalling molecule/s in B. licheniformis NCIMB 8874 was confirmed by the significant increase (p>0.05) in srfA expression in response to the addition of supernatants of B. licheniformis NCIMB 8874 cultures in their late exponential phase to low cell density cultures of B. subtilis reporter strains, carrying a srfA-lacZ fusion. The investigation of quorum sensing-regulated secondary metabolites production established production of lichenysin, -polyglutamic acid and extracellular proteases, whose biosynthesis is impaired in bacteria with disrupted comQXPA clusters. Bioinformatics studies on B. licheniformis NCIMB 8874 genome sequence confirmed the presence of essential quorum sensing-related genes, such as the comQXPA gene cluster, comK, mecA and comS. Moreover, in silico analysis allowed the identification of members of the Rap and Phr families, which aid the regulation of cell density dependent phenomena in B. subtilis. The results presented in this work positively indicate that B. licheniformis NCIMB 8874 cell-cell communication operates in analogy with the well established comQXPA-controlled pathway of B. subtilis.
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25

Yuan, Lihui. "Quorum sensing regulated gene expression in Porphyromonas gingivalis". [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010043.

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Thesis (Ph.D.)--University of Florida, 2005.
Typescript. Title from title page of source document. Document formatted into pages; contains 134 pages. Includes Vita. Includes bibliographical references.
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26

Li, Jun. "Systematic investigation of quorum sensing in Escherichia coli". College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6742.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Chemical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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27

Popat, Roman. "Communication, cooperation & conflict in quorum sensing bacteria". Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12468/.

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The scientific community has gathered an extremely detailed and sophisticated understanding of the genetic and molecular underpinnings of microbial communication. How these microbial communication systems arise and are maintained over evolutionary time-scales however has received relatively little attention. Some major questions remain unanswered such as; what is the function of small diffusible molecules? How does population structure affect the dynamics of social communication and what is the link between the ecology of communication and the virulence of a pathogenic population? Borrowing concepts from evolutionary theory can help to unravel these fundamental questions in the context of microbial communication as it has done in other taxa displaying social behaviours. In addition microbial model organisms in which molecular and genetic tools are abundant lend enormous power to empirical tests of evolutionary theory. This work combines both of these in an attempt to understand the evolution of bacterial communication using the model organism Pseudomonas aeruginosa and its well characterised Quorum Sensing systems. Specifically the focus is in three areas. Firstly this study reveals that the stability of bacterial signalling is vulnerable to perturbations in cost and benefit and genetic conflict. Secondly this study finds that spatial structure (biofilm vs planktonic) influences the outcome of social competition over signalling and reduces population viability. Thirdly this study finds that interspecific and intraspecific competition over public goods impose divergent selective pressures on communication.
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28

Jahan, Nasrin. "Structural studies of Vibrio cholerae quorum sensing proteins". Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2565.

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The spread of cholera is always associated with contaminated food or water and this is the reason this disease has been endemic in developing countries for centuries due to their lack of proper sanitation facilities and poor or no infrastructure for sewage systems. Cholera can spread quickly and sporadically after any natural disaster that destroys the sewage system or safe drinking water supply of both developed and undeveloped countries. In Southeast Asia in December 2004 and in Pakistan and Haiti 2010, cholera outbreaks followed the natural disasters; with most of the cholera victims being children. Although it is known that the best way to prevent cholera outbreak is the development of the infrastructure, provision of a safe drinking water supply and proper sanitation, this is a very long-term process, and most of the developing countries cannot afford such improvements. These situations can be made worse by natural disasters. Therefore there is a pressing need for the development of a cholera vaccine and there have been numerous research projects working towards this end for several decades. A few of them have been successful to date but because of the severe side effects and narrow range of protection, more effective and wider range vaccine development is still ongoing. In this study, crystallographic and enzymatic studies have been carried out on several novel proteins involved in the control of the production of the factors required for quorum sensing. Quorum sensing is a process in which bacterial cells communicate among themselves by the synthesis, release and detection of small chemical compounds called autoinducers. In this work, structural analysis was carried out on proteins involved in the synthesis and detection of the major autoinducer of Vibrio cholerae, named CAI-1. The crystal structure of CqsA involved in CAI-1 synthesis has been successfully solved and its enzymatic properties have been characterized. The structure of one domain of the cytoplasmic region of the CAI-1 receptor CqsS was also elucidated, and other domains were expressed. The crystal structure of another enzyme (VCA0859, an aldo-keto reductase) thought to have been involved in the synthesis of CAI-1 was also determined. Another protein named VCA0939 was also studied, due to its importance in biofilm development, and its ability to control quorum-sensing in an alternative pathway in the mutated version of pathogenic strains of V. cholerae that were responsible for the seventh cholera pandemic. The aim of this project was to understand the three dimensional structure of some proteins that are involved in quorum sensing and control of the expression of virulence genes for the pathogenesis of V. cholerae. Understanding the three dimensional structure of the proteins and the mode of autoinducer binding to its specific receptor could be highly valuable in the development of a chemical compound that could lead to the discovery of a novel drug with the ability to target cross species specification.
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29

Stavroulakis, Georgios. "Attenuation of quorum sensing using computationally designed polymers". Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4578.

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It is generally accepted that the majority of Gram-negative and Gram-positive bacteria communicate via production and sensing of small signal molecules, autoinducers. The ability of bacteria to sense their population density is termed quorum sensing (QS). Quorum sensing controls certain phenotypic traits, particularly virulence factors and biofilm formation. In this project a new solution for the attenuation of quorum sensing which involves selective sequestering of the signal molecules using rationally designed synthetic polymers was explored.
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30

Kirke, David F. "Protein-nucleic acid interactions regulating bacterial quorum sensing". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364668.

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Viegas, Ana. "Quorum sensing na prática clínica: mito ou realidade". Master's thesis, [s.n.], 2013. http://hdl.handle.net/10284/4087.

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Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Ciências Farmacêuticas
Este trabalho tem como objetivo analisar, através desta revisão bibliográfica, a possibilidade de se estudar mais detalhadamente o fenómeno de QS e avaliar a hipótese de se utilizar este mecanismo a favor do tratamento de algumas patologias. A influência dos microrganismos na saúde e/ou enfermidade da população, é uma questão incontornável. É de facto relevante que se efetuem estudos acerca do modo como estes seres sobrevivem, como comunicam entre si e, principalmente, averiguar quais as suas potencialidades para que futuramente possam ser exploradas em proveito da saúde humana. O estudo do QS, suas moléculas sinalizadoras e inibitórias é bastante complexo, devido à elevada quantidade e diversidade de moléculas envolvidas no processo. Este fenómeno permite aos microrganismos, mais especificamente às bactérias, a sobrevivência em comunidade e em condições pouco favoráveis, uma vez que possibilita a formação de uma estrutura designada por biofilme. Esta confere-lhes proteção contra as defesas do hospedeiro e contra os antibióticos. Assim, o estabelecimento de uma infeção torna-se rápido e eficaz. Esta situação é relativamente comum em pacientes com fibrose cística, transplantados, com feridas crónicas, com próteses ortopédicas ou outros dispositivos médicos (cateteres, válvulas, etc). A instalação do biofilme acarreta, para além dos custos económicos devido à repetição dos tratamentos, custos para o doente, nomeadamente, diminuição da qualidade de vida. O sucesso da sobrevivência das bactérias sob a influência do mecanismo de QS, levou os investigadores a colocarem a hipótese de utilizarem este processo nas mais diversas áreas, designadamente na área da saúde. Assim, graças à engenharia genética que permite adicionar ou remover genes de interesse às bactérias e colocá-las sob o controlo de outras através do QS, verificou-se que moléculas sinalizadoras e inibitórias tinham um grande potencial para a deteção e/ou tratamento de alguns tipos de cancro, impediam a formação de biofilmes sobre as superfícies das próteses, permitiam identificar os agentes etiológicos de determinadas infeções, constituíam uma excelente alternativa terapêutica no tratamento de feridas crónicas, entre outros. É neste contexto que se compreende a relevância do estudo e compreensão do QS, para que seja possível utilizá-lo na prática clínica, motivo pelo qual se efetuam inúmeras investigações, que até à data revelaram resultados bastante promissores. This work aims to analyze, through this literature review, the possibility of studying in detail the phenomenon of QS in order to identify potential ways of disruption and evaluate the possibility of using this mechanism in favor of the treatment of some diseases. The influence of microorganisms in health and / or illness of the population, is an unavoidable question. It is indeed important to be made, any studies about how these organisms survive, how they communicate with each other, and especially to ascertain what their potential future so that they can be exploited for the human health benefit. Study of QS signaling molecules and their inhibitory is quite complex, due to the high number and diversity of molecules involved in the process. This phenomenon allows micro-organisms, more particularly bacteria, to survival in community under undesirable conditions, since it enables the formation of a structure that provides protection against host defenses and against antibiotics, called biofilm. Thus, the establishment of an infection becomes faster and more effective. This situation is relatively common in patients with cystic fibrosis, transplant recipients, patients with chronic wounds or patients with orthopedic or other medical devices (catheters, valves, etc.). The installation of biofilm brings, apart from the economic costs due to repeated treatments, costs to the patient, in particular, decreased of life’s quality. The success of the bacteria’s survival under the influence of QS mechanism, led investigators to consider the hypothesis to use this process in several areas, particularly in health. Thus, by genetic engineering which enables adding or removing bacteria interesting genes and placed them under control of other bacteria, by QS was found that both inhibitory and signaling molecules have a great potential for the detection and / or treatment of some types of cancer, prevented the formation of biofilms on the surfaces of prostheses, allowed to identify the etiologic agents of certain infections and were an excellent therapeutic option in the treatment of chronic wounds. It is in this context, lies the importance of studying and understanding the QS, so you can use it in clinical practice, which is why numerous investigations are carried out, which to date have shown very promising results.
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32

Koziski, Jessica Marie. "Genetic Analysis of the Quorum Sensing Regulator EsaR". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/34229.

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Pantoea stewartii subsp. stewartii is the causative agent of Stewartâ s wilt disease in maize plants. The bacteria are injected into the plant by corn flea beetles during feeding. They colonize the xylem and overproduce a capsular exopolysaccharide (EPS) at high cell densities. The production of EPS is regulated by an EsaI/EsaR quorum sensing mechanism, homologous to the LuxI/R system. Although activation of the EPS encoding genes by EsaR occurs after it complexes to the AHL (3-oxo-C6-HSL), unlike the LuxI/R system, this activation occurs by a different mechanism. At low cell densities, dimerized EsaR acts as a repressor. At a high cell population, derepression of the EPS genes occurs via an unknown mechanism once the AHL complexes to EsaR. Hence, a random mutagenesis genetic approach to isolate EsaR* variants that are immune to the effects of AHL has been utilized. Error-prone PCR and site-directed mutagenesis were used to generate desired mutants, which were subsequently screened for their ability to repress transcription in the presence of AHL. Several individual amino acids playing a critical role in the AHL-insensitive phenotype have been identified and mapped onto a homology model of EsaR. A separate study attempted to localize the dimerization region and analyze the stability of the N-terminal domain of EsaR. Truncations of EsaR at amino acids 169 and 178, without and with the extended linker region respectively, were generated using PCR. Dimerization assays similar to those by Choi and Greenberg in 1991 were performed but proved to be unsuccessful. However, the N-terminal domain is stable as determined by western blotting, which may facilitate its future structural analysis. Together, these efforts have contributed to the molecular understanding of AHL-dependent derepression of EsaR.
Master of Science
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33

Jones, Faye-Ellen. "Inhibition of N-acyl-homoserine lactone quorum sensing". Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602017.

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Quorum-sensing amongst Gram-negative bacteria is an important method of intercellular communication required for conveying information about population density. The extracellular accumulation of the signal molecule involved, N-acyl homoserine lactone (AHL), leading to increases in internal physiological concentration, allows phenotypic switching to occur that is beneficial to the bacterial population. In our laboratory, analysis of the effect of AHL on phenotype currently involves creating null mutants unable to produce AHL, then reintroducing the signal molecule exogenously. With the increasing number of human, animal and plant pathogens utilising AHL quorum-sensing for regulating viirulence, AHLs have become prime targets for anti-infective therapy and crop-protection. The research described here has investigated methods of inhibition of quorum-sensing through the AHL signal molecule. These include the application of extremes of temperature and pH, and isolation and characterisation of the first recombinant human antibody fragment specific to AHLs from a naive phage display library, which could be used to examine cell-cell communication without the need for gene manipulation.
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34

Sharif, Dilara Islam. "Quorum sensing in the cyanobacterium Gloeothece PCC 6909". Thesis, Swansea University, 2008. https://cronfa.swan.ac.uk/Record/cronfa42295.

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The thesis sought to study whether cyanobacteria utilise the process of quorum sensing during their growth, to identify any quorum sensing molecules produced by the cyanobacteria Gloeothece PCC 6909/1 and to study the effect of any such molecules in aexenic cultures of the organism. The study presents the first evidence of N-octanoyl homoserine lactone (C8-HSL) quorum sensing molecule from axenic cultures of the cyanobacterium PCC 6909 and its sheathless mutant PCC 6909/1 and that the production of this molecule followed a density dependent accumulation, a common feature of many quorum sensing systems. The response of the Gloeothece proteome to exogenous concentrations of C8-HSL was examined, indicating changes in 43 protein spots on a 2D-PAGE gel, thereby indicating a response through global changes in protein expression. Among the 15 proteins that showed more than 2 fold expression changes, RuBisCo, glutamate synthase, chorismate synthase, a LysR family of transcriptional regulator (all up regulated) enolase and aldolase (down regulated) could be identified. A number of phosphorylated proteins also showed increased accumulation suggesting changes in the phosphoproteome of Gloeothece. A response to C8-HSL was also detected in physiological changes of the organism through decreased accumulation of extracellular soluble carbohydrates and an increased acid phosphatase activity from cell extracts. In conclusion, this study presents evidence that the cyanobacterium Gloeothece employs a C8-HSL based quorum sensing system through the accumulation and response to a C8-HSL signal. These findings can help increase our understanding of how colonial cyanobacteria encounter stress at high cell densities.
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35

Portela, Gislaine Simões. "Bioprospecção de plantas medicinais Com atividade antimicrobiana e anti-quorum sensing". Universidade Federal da Paraí­ba, 2011. http://tede.biblioteca.ufpb.br:8080/handle/tede/6650.

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Made available in DSpace on 2015-05-14T12:56:01Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 944601 bytes, checksum: c211a613a7ca088bee34c901c685111c (MD5) Previous issue date: 2011-12-16
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The objective of this research was to investigate the existence of antimicrobial plant compounds and anti-quorum sensing in oral biofilms. The plants used in this study were: Schinus terebinthifolius Raddi (aroeira da praia); Lippia sidoides Scham (alecrim pimenta); Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão); Anacardium occidentale Linn (cajueiro); Psidium guajava Linn (goiabeira); Tabebuia avellanedae Lorentz ex Griseb (ipê-roxo); Hymenaea courbaril L. (jatobá) e a Bowdichia virgiloides Kunth (sucupira), Anadenanthera macrocarpa Benth (angico), Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão), Ziziphus joazeiro Mart (joazeiro), Sida cordifolia L. (malva branca), Chenopodium ambrosioides L. (mastruz), Punica granatum L. (romã) and Zingiber officinale (gengibre). The extracts were submitted in good yield to the partition with solvents in order of increasing polarity, hexane, dichloromethane and ethyl acetate. The antimicrobial activity was determined by the techniques of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) and use the model QSIs (Quorum Sensing Inhibitor System) proposed by Rasmussen and colleagues (2005). The results proved promising for the development of phytomedicines. The anti-quorun sensing was significant for Abarema cochiliacarpos (Gomes) B. & JW Grimes (barbatimão), Anacardium occidentale Linn (cajueiro), Psidium guajava Linn (goiabeira) and the fruit of Hymenaea courbaril L. (Jatobá). The results support the hypothesis that extracts and partitions of some medicinal plants have anti-quorum sensing activity as a mechanism of antimicrobial activity.
O objetivo desta pesquisa foi investigar a existência de compostos vegetais que apresentem atividade antimicrobiana e anti-quorum sensing em micro-organismos formadores de biofilmes bucais. As plantas utilizadas nesta pesquisa foram: Schinus terebinthifolius Raddi (aroeira da praia); Lippia sidoides Scham (alecrim pimenta); Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão); Anacardium occidentale Linn (cajueiro); Psidium guajava Linn (goiabeira); Tabebuia avellanedae Lorentz ex Griseb (ipê-roxo); Hymenaea courbaril L. (jatobá) e a Bowdichia virgiloides Kunth (sucupira), Anadenanthera macrocarpa Benth (angico), Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão), Ziziphus joazeiro Mart (joazeiro), Sida cordifolia L. (malva branca), Chenopodium ambrosioides L. (mastruz), Punica granatum L. (romã) e Zingiber officinale (gengibre). Os extratos de Schinus terebinthifolius Raddi (aroeira da praia); Lippia sidoides Scham (alecrim pimenta); Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão); Anacardium occidentale Linn (cajueiro); Psidium guajava Linn (goiabeira); Tabebuia avellanedae Lorentz ex Griseb (ipê-roxo); Hymenaea courbaril L. (jatobá) e a Bowdichia virgiloides Kunth (sucupira), Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão), Ziziphus joazeiro Mart (joazeiro) foram submetidos à partição com solventes em ordem crescente de polaridade, hexano, diclorometano e acetato de etila. A atividade antimicrobiana foi determinada pela técnica da microdiluição em caldo e utilizou o modelo de QSIs (sistema Inibidor de Quorum Sensing) proposto por Rasmussen e colaboradores (2005). Os resultados obtidos revelaram-se promissores para o desenvolvimento de fitomedicamentos. A atividade anti-quorun sensing foi significante para Abarema cochiliacarpos (Gomes) B. & J.W. Grimes (barbatimão); Anacardium occidentale Linn (cajueiro); Psidium guajava Linn (goiabeira); e o fruto do Hymenaea courbaril L. (jatobá). Os resultados suportam a hipótese que extratos e partições de algumas plantas medicinais possuem atividade anti-quorum sensing como mecanismo de atividade antimicrobiana.
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Pietschke, Cleo I. [Verfasser]. "Inter-kingdom communication : quorum sensing and quorum quenching in the metaorganism Hydra / Cleo I. Pietschke". Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1173163190/34.

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Bergonzi, Céline. "Étude, caractérisation et ingénierie de lactonases pour l'inhibition de la virulence et des biofilms bactériens". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0241.

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Certains microorganismes sont capables de communiquer en utilisant des molécules et d’utiliser ce système pour réguler des comportements en fonction de la densité cellulaire. Ce système de communication, appelé quorum sensing (QS), régule des comportements bactériens, tels que la virulence et la formation de biofilm. Les molécules signal les plus étudiées sont les acyle-homosérine lactones (AHLs). Les enzymes qui sont capables de dégrader ces molécules peuvent couper la communication bactérienne, et se comportent ainsi comme des inhibiteurs de virulence et de biofilm. Ce phénomène, appelé quorum quenching (QQ), est une approche prometteuse pour le contrôle bactérien sans les tuer, ainsi que pour le développement de nouvelles thérapies contre les bactéries résistantes aux antibiotiques. Les travaux menés durant ma thèse ont permis d’isoler et de caractériser biochimiquement, enzymatiquement et structuralement de nouvelles lactonases provenant d’organismes thermophiles, capables d’inhiber le QS. J’ai résolu les structures de trois lactonases et en complexe avec différents types de lactones. Ces données ont révélées l’extrême polyvalence des sites actifs de ces enzymes, et ont permis d’identifier les résidus potentiellement impliqués dans la spécificité de substrat de ces enzymes. Ces résultats serviront de bases aux futurs projets d’ingénierie visant à changer la spécificité de ces enzymes. Enfin, mes travaux de caractérisation sur ces lactonases très stables ont permis de les utiliser hors du laboratoire et de démontrer l’importance de la signalisation bactérienne dans des processus biologiques complexes tels que la formation de biofilm et la bio-corrosion
Numerous microorganisms are able to communicate using molecules and use this signaling system to coordinate behaviors in a cell-density-dependent manner. This communication system, dubbed quorum sensing (QS), regulates bacterial behaviors such as biofilm formation. The most popular system utilizes acyl homoserine lactones (AHLs) as signals. Enzymes that can degrade these signaling molecules can effectively disrupt bacterial signaling, and thereby behave as potent biofilm and virulence inhibitors. Therefore, the inhibition of QS, termed quorum quenching (QQ) by these enzymes is a promising approach to control microbes without killing them and develop therapies on multidrugs resistant strains. During this thesis, I have isolated and characterized biochemically, enzymatically and structurally novel lactonases from thermophilic sources. I have determined the structures of three lactonases in complex with different types of lactones. This enabled me to elucidate their catalytic mechanisms, as well as the unique binding modes of structurally different lactones. These data revealed the extreme catalytic versatility of the active sites of these enzymes, and allowed for the determination of residues possibly involved in substrate specificity. These data, in combination with structural data obtained on improved lactonase mutants, will serve as a foundation to guide future engineering studies aiming at altering lactonases’ specificity. Lastly, isolation and characterization work on these thermostable lactonases allowed to demonstrate the importance of bacterial signaling in complex biological processes, in the field, including biofilm formation and biocorrosion
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38

Rémy, Benjamin. "Développement d'une nouvelle génération de pansements antimicrobiens à base d'enzyme à activité lactonase". Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0391.

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Des bactéries utilisent un système de communication, quorum sensing (QS), qui leur permet de synchroniser leur comportement proportionnellement à la densité de population. Des bactéries pathogènes utilisent le QS pour coordonner leur virulence et la formation de biofilm. Bloquer le QS, quorum quenching (QQ), constitue donc une piste pour étendre l'arsenal thérapeutique antibactérien. Durant cette thèse, SsoPox, une lactonase hyperstable hydrolysant les acyl homosérine lactones (AHL) impliquées dans le QS de bactéries à Gram négative pathogènes comme P. aeruginosa, a été étudiée. Son utilisation dans des pansements contre les infections à P. aeruginosa a été évaluée. La résistance aux contraintes industrielles liées aux procédés de fabrication des pansements a été évaluée. SsoPox s'est montrée résistante à la chaleur, aux solvants organiques, au stockage à température ambiante et à la stérilisation. L’efficacité de l’enzyme a été montrée sur 2 souches modèles et 51 isolats cliniques de P. aeruginosa. SsoPox a été plus efficace que 2 inhibiteurs du QS. L’efficacité de l’enzyme est aussi conservée après immobilisation. Une étude phénotypique et moléculaire du QQ enzymatique de P. aeruginosa a été réalisée entre SsoPox et une autre lactonase GcL ayant un spectre d'action distinct sur les AHL. In vitro, il a été mis en évidence des impacts différents entre les 2 enzymes sur les facteurs de virulence et le biofilm. In vivo, il a été montré que seul SsoPox réduit la virulence de P. aeruginosa. L’expression des gènes du QS et le protéome ont confirmé des différences entre GcL et SsoPox. Ainsi SsoPox semble constituer un bon candidat pour le développement de pansements innovants
Bacteria use a communication system, or quorum sensing (QS), to synchronize group behaviors according to population density. Some pathogens use QS to coordinate virulence and biofilm formation. Interfering with QS, or quorum quenching, represents a target to extent antibacterial drug resources. Along this PhD project, SsoPox, a hyperstable lactonase, hydrolyzing acyl homoserine lactones (AHL) involved in the QS of Gram-negative pathogen bacteria like Pseudomonas aeruginosa was studied. SsoPox was studied and characterized for its use in wound dressing against P. aeruginosa infection. The enzyme resistance to industrial constraints encountered during wound dressings manufacturing processes was estimated. SsoPox demonstrated a high tolerance to heat, organic solvents, ambient temperature storage and to sterilization processes. The enzyme efficiency was shown on 2 model strains and 51 clinical isolates of P. aeruginosa. SsoPox was also more efficient than 2 well characterized QS inhibitors. The enzyme kept its efficiency even when immobilized. A last part was dedicated to phenotypical and molecular study of enzymatic QQ of P. aeruginosa. SsoPox and another lactonase GcL, having distinct AHL specificities, were compared. In vitro experiments highlighted different impacts between the enzymes on virulence factors and biofilm. An in vivo study showed that SsoPox, unlike GcL, was able to reduce P. aeruginosa virulence. QS gene expression and proteome study confirmed distinct impacts between each enzyme treatment s. Thus, SsoPox seems to be a prime candidate for development of innovative medical devices
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39

Doberva, Margot. "Le quorum sensing bactérien dans l'environnement marin : diversité moléculaire et génétique des auto-inducteurs". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066049/document.

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L'environnement marin est constitué d'écosystèmes nombreux et variés, qui sont habités par des organismes appartenant aux trois domaines du vivant dont celui des bactéries. La coopération bactérienne est basée sur un mécanisme moléculaire appelé quorum sensing (QS). Ce système est dépendant de la densité cellulaire de la communauté, ce qui permet aux bactéries de synchroniser leur expression génétique, pour coordonner certaines de leurs activités physiologiques. Les bactéries produisent plusieurs types de molécules signal dont les acyl-homosérines lactones (AHLs ou AI-1) et le furanosyl diester borate (AI-2). La majorité des recherches dans le domaine du QS s'est portée sur des modèles bactériens d'intérêt biomédical ou agronomique. Cependant, l'importance du QS chez les bactéries marines reste mal connu. Ce travail de thèse a pour question: Quelle est la prévalence des AI chez les bactéries marines ? Pour aborder cette problématique : trois axes : Le criblage de la collection de bactéries marines MOLA, qui est basé sur des techniques de chimie des substances naturelles, et a permis de mettre en exergue des souches bactériennes originales comme Maribius sp MOLA 401, qui produisent un très grand nombre d'AHLs avec de nouvelles structures. Le second axe s'appuie sur des méthodes de bio-informatique pour réaliser le criblage du métagénome marin du Global Ocean Sampling pour la recherche de gènes luxI, ainS, hdtS et luxS. L'ensemble de ces données sur la diversité, l'abondance et la répartition biogéographique des AI-1 dans l'écosystème marin suggère une forte importance des mécanismes du QS à l'¿uvre dans les communautés bactériennes marines naturelles
The marine environment is composed of many and varied ecosystems, which are inhabited by organisms belonging to the three domains of life including the bacteria. Bacterial cooperation is based on a molecular mechanism called quorum sensing (QS). This system is dependent on the cell density of the community, which allows bacteria to synchronize their gene expression, to coordinate some of their physiological activities. Bacteria produce several types of signal molecules with acyl-homoserines lactones (AHLs or AI-1) and the furanosyl borate diester (AI-2). The majority of research in the field of QS has focused on bacterial models for biomedical and agricultural interest. However, the importance of QS in marine bacteria remains unclear. This work has the question: What is the prevalence of AI in marine bacteria? To address this problem two axes: Screening the collection of marine bacteria MOLA, which is based on chemistry techniques of natural substances, and allowed to highlight original bacterial strains as Maribius sp MOLA 401, which produce very large number of AHLs with new structures. The second axis is based on the methods of bioinformatics to perform screening of metagenome marine Global Ocean Sampling for research luxI, ainS, luxS and hdtS genes,. All these data on diversity, abundance and biogeographical distribution of AI-1 in the marine ecosystem suggests a strong importance of QS mechanisms at work in the natural marine bacterial communities
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40

Huedo, Moreno Pol. "Fatty acid-mediated quorum sensing systems in stenotrophomonas maltophilia". Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/285570.

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Els sistemes de comunicació bacteriana -coneguts com quorum sensing (QS)- a través de molècules senyalitzadores del tipus àcid gras han despertat molt d’interès en els darrers anys ja que s’ha vist que molts bacteris patògens els utilitzen per regular funcions relacionades amb la virulència. Es coneix que Stenotrophomonas maltophilia presenta el sistema de QS DSF (Diffusible Signal Factor) el qual és controlat pels gens que conformen el clúster rpf (Regulation of Pathogenecity Factors). No obstant, no està clar els mecanismes pels quals S. maltophilia sintetitza i sensa les molècules senyal així com quines funcions estan regulades per aquest sistema. En aquest treball hem demostrat que existeixen dues poblacions de S. maltophilia les quals es diferencien en base al clúster rpf (rpf-1 o rpf-2) que presenten. Cada variant difereix bàsicament en els gens que codifiquen per la sintasa RpfF i el sensor RpfC. A més, hem observat que existeix una associació entre ambdós components, generant-se la parella RpfF-1/RpfC-1 per les soques rpf-1 i RpfF-2/RpfC-2 per les soques rpf-2. Addicionalment, hem demostrat que només aquelles soques que presenten la variant rpf-1 produeixen nivells detectables de DSF i aquest regula motilitat bacteriana, formació de biofilm i virulència. Per altra banda, les soques de la variant rpf-2 necessiten més còpies de la sintasa RpfF-2 o l’absència del repressor RpfC-2 per produir DSF. En aquest cas, el sistema de QS DSF sembla només regular pocs fenotips relacionats amb virulència en situacions molt específiques. També hem mostrat que existeix un feedback positiu en la síntesi de DSF i que ambdós grups de soques actuen de manera sinèrgica en la producció de DSF i la virulència de tota la població. Addicionalment, hem observat que, mentre la variant RpfC-1 és un sensor promiscu el qual permet l’alliberació de la sintasa RpfF-1 tant punt detecta no només DSF sinó també àcids grassos de cadena mitja, el sensor RpfC-2 és molt més específic, alliberant RpfF-2 només quan detecta DSF. A més a més, aquí també mostrem com el sistema de QS cis-DA (cis-decenoic) descrit recentment a Pseudomonas aeruginosa és també present a S. maltophilia i regula un alt nombre de factors de virulència. En aquesta línia, hem sigut capaços de caracteritzar preliminarment dos components importants en la biosíntesi de l’àcid gras cis-DA: les enoil coA hidratases (ECH) Smlt0266 i Smlt0267. Hem observat que, mentre la mutació de la hipotètica sintasa Smlt0266 només condueix a l’increment de la formació de biofilm, la mutació en el gen que codifica per la ECH alternativa Smlt0267 implica una reducció dràstica en la formació de biofilm, la motilitat bacteriana, la producció d’exopolisacàrids, la resistència a antibiòtics i la virulència. Resultats similars s’han obtingut per els mutants dels gens ortòlegs a P. aeruginosa, la qual cosa recolza la importància d’aquestes dues ECHs, a més a més del sistema DSF, en la regulació de la virulència i aporta noves dianes interessants pel desenvolupament de teràpies antimicrobianes contra aquest potencial patogen humà
Fatty-acid mediated Quorum Sensing (QS) systems have aroused considerably interest in the last years since it has been reported that many important bacterial pathogens use these communication systems to regulate virulence-related functions. It is known that Stenotrophomonas maltophilia presents the DSF (Diffusible Signal Factor) QS system, which is controlled by components that are encoded in the rpf cluster (Regulation of Pathogenicity Factors). However, the mechanisms by which S. maltophilia synthesize and sense as well as the biological functions that are under control of DSF-QS remain unclear. Here, we have first demonstrated that two populations of S. maltophilia can be distinguished depending on the rpf cluster (rpf-1 or rpf-2) they harbour. Each variant cluster differs basically in the genes that encode for the synthase RpfF and the sensor RpfC. Moreover, we have observed that there exist a full association between both components, existing the pair RpfF-1/RpfC-1 for the rpf-1 variant and RpfF-2/RpfC-2 for the rpf-2 variant. In addition, we have demonstrated that only strains harbouring the rpf-1 variant produce detectable levels of DSF and it seems to regulate bacterial motility, biofilm development and virulence. On the other hand, strains harbouring the rpf-2 variant need extra copies of rpfF-2 or the absence of rpfC-2 to achieve detectable levels of DSF. In this case, DSF-QS seems to control only some virulence-related phenotypes in very specific environments (e.g., zebrafish infection). We also have shown that DSF is produced in a positive feedback-manner in S. maltophilia, and also, that both rpf-variant groups act synergistically in the DSF production and virulence ability of the whole population. In addition, we have observed that while RpfC-1 is a promiscuous sensor that liberates free active-RpfF-1 -with the subsequent DSF synthesis- upon detection not only DSF, but also saturated medium-length fatty acids, the sensor RpfC-2 only allows activation of RpfF-2 upon detection of DSF-itself, indicating that this sensor component is much more specific. Here, we further report that the cis-DA (cis-decenoic acid) QS system recently described in Pseudomonas aeruginosa is also present in S. maltophilia, and it regulates various virulence factors. In this line, we have preliminary characterized two important components in the biosynthesis of cis-DA, the enoyl-CoA hydratases (ECH) Smlt0266 and Smlt0267. We have observed that while the mutation in the putative synthase smlt0266 lead to alteration basically in biofilm formation, the mutation of the alternative ECH smlt0267 results in a drastic effect in many virulence-related behaviours such as biofilm formation, bacterial motility, exopolysaccharide production, antibiotic resistance and virulence. Similar results have been obtained for the mutants in the orthologous P. aeruginosa genes ∆dspI and ∆dspII. These results further support the significance of these two ECH, in addition to DSF-QS system, in virulence regulation of S. maltophilia and provide new interesting targets for developing new antimicrobial therapies against this potential human pathogen.
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Schmidt, Silvia. "Biological control activity and quorum sensing in Burkholderia sp /". [S.l.] : [s.n.], 2009. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000278486.

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Lupp, Claudia. "Quorum sensing in the Vibrio fischeri-Euprymna scolopes symbiosis". Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/1260.

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Quorum sensing is a cell density-dependent bacterial gene regulatory mechanism used for the expression of colonization-related genes. The symbiotic relationship between the luminescent bacterium Vibrio fischeri and the Hawaiian bobtail squid Euprymna scolopes serves as a model system to study the molecular processes underlying bacterial colonization. This system is especially well-suited for the investigation of the impact of quorum sensing on colonization because (i) it is an easily accessible, natural, two-species colonization model, and (ii) quorum sensing regulates luminescence expression in V. fischeri, which allows the non-invasive detection of quorum-sensing activity both in culture and in symbiosis. While the impact of one of V. fischeri's quorum-sensing systems, lux, on luminescence expression and symbiotic competence has been extensively studied, little was known about other putative systems. The results of this study demonstrate that the V. fischeri ain system is essential for both maximal luminescence expression and symbiotic competence. The ain system predominantly induces luminescence expression at intermediate cell densities, which occur in culture, while the lux system is responsible for luminescence expression at the high cell densities found in symbiosis, suggesting the sequential induction of luminescence gene expression by these two systems. Furthermore, the ain quorum sensing system is important for the processes underlying colonization initiation, while the impact of the lux system is apparent only in later stages of the symbiosis, indicating distinct functions of these two systems during the colonization process. A global transcriptome. analysis of quorum-sensing mutants revealed that ain quorum sensing represses motility gene expression, providing a likely explanation for the initiation defect. Although it has been known that many bacterial species possess multiple quorum-sensing systems, this is the first study demonstrating that two quorum-sensing systems are employed to specifically regulate functions important at distinct cell densities occurring during the colonization process.
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Fagerlind, Magnus Biotechnology &amp Biomolecular Sciences Faculty of Science UNSW. "Mathematical modelling of bacterial quorum sensing and biofilm formation". Awarded by:University of New South Wales. Biotechnology & Biomolecular Sciences, 2008. http://handle.unsw.edu.au/1959.4/43095.

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To date, bacterial resistance to antibiotics is an increasing problem and there is a growing appreciation that biofilm formation is a significant contributor to antibiotic resistance. This has led to .increased research on ways to reduce/control biofilm formation. One such target is bacterial cell-cell communication that allows bacteria to coordinate gene expression, and that has been shown to be involved in biofilm formation and production of virulence factors. By interfering with this communication system it should be possible to control gene expression and thus inhibit production of virulence factors as well as the formation of biofilms. However, these processes are multi-factorial, which make it a very complicated task to experimentally identify key parameters that subsequently could guide the development of cell-cell communication strategies to control bacterial virulence and biofilm formation. However, by using mathematical modelling, it is possible to study complex processes and to identify those parameters that are most important for these processes. The focus of this thesis was to develop mathematical models of bacterial cell-cell communication systems and biofilm formation to identify key parameters that could subsequently guide the development of cell-cell communication strategies to control bacterial virulence and biofilm formation. It was found that the cell-cell communication system in the model bacterium Pseudomonas aeruginosa works by hysteretic switching between two stable steady states, reflecting low and high rates of signal production, respectively. It was also shown that this bacterium uses different regulators to adjust the cell density required for switching the system on or off. Moreover, it was also demonstrated that signal antagonists have the capacity to switch the system from an induced state to the lower, uninduced state. However, it was also shown that this blocking behaviour is extremely dependent on the properties of the AHL antagonists, since even very small differences could greatly affect the outcome. Finally, accumulation of damage was predicted to be the main cause of cell death during the formation of biofilms. In addition, a strong relationship between nutrient availability and damage accumulation (and consequently cell death) was also found.
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44

Peng, Hanjing. "Development of Bacterial Quorum Sensing Inhibitors and Molecular Probes". Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/chemistry_diss/73.

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Bacterial quorum sensing is regarded as a novel target for the design of antimicrobials. Based on lead structures identified from HTS, 39 analogues have been synthesized and evaluated in Vibrio haveyi. Potent inhibitors with IC50 values at single-digit micromolar concentrations for AI-2 mediated quorum sensing have been identified. On the second project, post-synthesis modifications of DNA provide easy functionalizations for expanded applications such as aptamer selection. A CBT-modified thymidine analogue (CBT-TTP) has been synthesized and used for enzymatic incorporation into DNA. Post-synthesis modifications through condensation with 1,2-aminothiol for installation of a boronic acid moiety or a fluorophore have been achieved. On the third project, H2S has been recognized as an important gasotransmitter and its concentration is relevant to a variety of diseases. A novel fluorescent probe (DNS-Az) has been developed for quantitation of H2S in aqueous solutions. This probe has been used to measure H2S concentrations in the blood.
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Lam, Howard Andrew. "Cranberry derived materials modulate quorum sensing in Pseudomonas aeruginosa". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114290.

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Cranberry-derived materials (CDMs) have recently been shown to block the group associated swarming motility in Pseudomonas aeruginosa without blocking swimming or twitching motilities. However, their mechanism of action is as of yet unknown. We hypothesized that these CDMs interfere with communication pathways important in swarming called quorum sensing (QS) and measured the impact of the CDMs on QS at three levels: QS signalling gene transcription, QS signal production, and activity/production of QS-controlled virulence factors. Crude cranberry powder extract (CP) repressed the las and rhl systems, the two main QS systems in P. aeruginosa, – as measured by the use of a lacZ bioreporter and β-galactosidase assay. CP also reduced the accumulation of both las and rhl QS signals in the medium. Exposure to 5 mg/mL or 10 mg/mL CP stimulated cell growth but still resulted in the reduction of the growth-normalized activity of key virulence factors. Cranberry-derived proanthocyanidins (cPACs) had little direct effect on the regulatory QS gene transcription or QS signal production in P. aeruginosa but reduced the activity/production of key virulence factors. Compounds found in cranberries may be clinically useful; however, further research is required to isolate the active compound(s) from CP and overcome the associated increased cell growth.
Les matériaux dérivés des canneberges (MDC) ont été récemment démontré ayant la capacité de bloquer le mode de déplacement communautaire de type swarming au Pseudomonas aeruginosa sans bloquer les modes de déplacement individuels de type swimming et twitching. Pourtant, leur mode d'action est inconnu. Nous avons supposé que ces MDC interférent avec une voie de communication essentiel pour le mode de déplacement de type swarming appelé quorum sensing (QS), et nous avons mesuré l'impact des MDC sur QS à trois niveaux : la transcription des gènes de signalisation QS, la production des signaux QS, et l'activité/production des facteurs de virulence contrôlées par le QS.L'extrait de canneberges en poudre brut (CP) a réprimé la transcription des gènes de signalisation dans les systèmes las et rhl, les deux systèmes de QS majeurs au P. aeruginosa, utilisant un rapporteur biologique lacZ et un essai β-galactosidase. Le CP a aussi causé une réduction de l'accumulation des signaux pour les systèmes las et rhl dans le médium. L'addition du CP aux concentrations de 5 mg/mL ou 10 mg/mL a stimulé la croissance des cellules mais a aussi réduit l'activité et la production de plusieurs facteurs de virulence. Les proanthocyanidines d'origine de canneberges (cPACs) ont eu peu d'effet sur les systèmes QS de P. aeruginosa mais ont quand même réduit l'activité et la production de plusieurs facteurs de virulence, normalisée pour la croissance des cellules. Les MDC pourraient un jour être cliniquement utiles, mais des recherches supplémentaires sont nécessaires pour isoler le(s) composé(es) actif(s) du CP et de surmonter le problème de la croissance cellulaire augmenté.
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46

Ruparell, Avika. "Interplay between quorum sensing and metabolism in Pseudomonas aeruginosa". Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12690/.

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The important human pathogen Pseudomonas aeruginosa causes a broad-spectrum of diseases including life threatening infections. A cell density-dependent regulatory network termed quorum sensing (QS) is pivotal in the control of P. aeruginosa pathogenicity, and the signal molecules employed are N-acyl-L-homoserine lactones (AHLs) and the Pseudomonas quinolone signal (PQS). Production of these QS signal molecules (QSSMs) requires precursors including fatty acids, S-adenosyl-L-methionine (SAM) and aromatic amino acids. SAM is derived from the activated methyl cycle (AMC) which is an important pathway dedicated to the degradation of the toxic metabolite S-adenosyl-L-homocysteine (SAH). Through removing the genes encoding the AHL synthases, RhlI and LasI from the complex hierarchical system of P. aeruginosa by expressing them in the heterologous host, Escherichia coli, this study has measured the influence of AHL production upon bacterial metabolism. AHL profiles were broader than previously reported, correlated with a reduction in the intracellular concentrations of several metabolites, and were more pronounced in the E. coli strain producing the LasI synthase than the RhlI enzyme. Production of foreign QSSM synthases had a knock-on effect on the native E. coli QSSM, autoinducer-2 (AI-2). We hypothesize that AI-2 production was significantly reduced since it also requires AMC metabolites for its synthesis. The influence that these metabolic perturbations had on cell fitness was manifest through reduced growth in minimal media. Complementation of growth by exogenously added metabolites confirmed our hypothesis that QSSM synthesis creates a drain on metabolite levels with consequences for cell fitness. Site-directed mutagenesis of key catalytic residues in the QSSM synthases was performed to directly prove that the effects observed were due to the function of the synthases, and not the production of a heterologous protein. Moreover, complete profiling of P. aeruginosa PA01 AHL synthase mutants is unravelling the interrelationship between metabolism and cell-to-cell communication in P. aeruginosa.
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47

Williams, Headley St Edward. "Investigation of a Quorum sensing molecule in Aspergillus Nidulans". Thesis, University of Westminster, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507844.

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48

Hale, Lisa Ann. "The Role of Quorum Sensing in Rhodobacter sphaeroides WS8N". Thesis, Oxford Brookes University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515275.

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49

Middleton, Barry John. "Quorum sensing cross-talk in cystic fibrosis lung pathogens". Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288998.

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50

Enfield, Catherine L. "Quorum sensing, DNA replication and virulence in Escherichia coli". Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435397.

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