42 research outputs found
Contraintes à l'origine de la souffrance des internes en médecine (analyse par entretiens semi-dirigés)
Résumé françaisGRENOBLE1-BU Médecine pharm. (385162101) / SudocSudocFranceF
A Flavor Lactone Mimicking AHL Quorum-Sensing Signals Exploits the Broad Affinity of the QsdR Regulator to Stimulate Transcription of the Rhodococcal qsd Operon Involved in Quorum-Quenching and Biocontrol Activities
In many Gram-negative bacteria, virulence, and social behavior are controlled by quorum-sensing (QS) systems based on the synthesis and perception of N-acyl homoserine lactones (AHLs). Quorum-quenching (QQ) is currently used to disrupt bacterial communication, as a biocontrol strategy for plant crop protection. In this context, the Gram-positive bacterium Rhodococcus erythropolis uses a catabolic pathway to control the virulence of soft-rot pathogens by degrading their AHL signals. This QS signal degradation pathway requires the expression of the qsd operon, encoding the key enzyme QsdA, an intracellular lactonase that can hydrolyze a wide range of substrates. QsdR, a TetR-like family regulator, represses the expression of the qsd operon. During AHL degradation, this repression is released by the binding of the Îł-butyrolactone ring of the pathogen signaling molecules to QsdR. We show here that a lactone designed to mimic quorum signals, Îł-caprolactone, can act as an effector ligand of QsdR, triggering the synthesis of qsd operon-encoded enzymes. Interaction between Îł-caprolactone and QsdR was demonstrated indirectly, by quantitative RT-PCR, molecular docking and transcriptional fusion approaches, and directly, in an electrophoretic mobility shift assay. This broad-affinity regulatory system demonstrates that preventive or curative quenching therapies could be triggered artificially and/or managed in a sustainable way by the addition of Îł-caprolactone, a compound better known as cheap food additive. The biostimulation of QQ activity could therefore be used to counteract the lack of consistency observed in some large-scale biocontrol assays
Implication of type VI secretion system in motility and bacterial communication, and specific properties of the environmental strain P. fluorescens MFE01
Les travaux menĂ©s durant cette thĂšse portent sur lâĂ©tude de propriĂ©tĂ©s particuliĂšres de la souche P. fluorescens MFE01. La premiĂšre partie porte sur la relation entre le systĂšme de sĂ©crĂ©tion de type 6 (SST6) et la mobilitĂ©. En effet, cette souche environnementale avirulente possĂšde un SST6 trĂšs actif qui lui confĂšre un avantage lors de compĂ©tition avec dâautres microorganismes, notamment dans un pathosystĂšme vĂ©gĂ©tal. La prĂ©sence de plusieurs gĂšnes hcp codant pour des protĂ©ines de lâaiguille du SST6, situĂ©s en dehors du cluster principal, semble permettre la formation de diffĂ©rentes aiguilles du SST6, ayant des fonctions spĂ©cifiques. Parmi les protĂ©ines Hcp, la protĂ©ine Hcp1 est impliquĂ©e dans lâinhibition de la mobilitĂ© flagellaire des bactĂ©ries cibles, et, de façon remarquable, la dĂ©lĂ©tion du gĂšne codant cette protĂ©ine, le gĂšne hcp1, inhibe la mobilitĂ© de type « swim » de la souche MFE01. Ainsi, les travaux menĂ©s ont permis de formuler des hypothĂšses sur le rĂŽle du SST6 formĂ© de la protĂ©ine Hcp1 et la formation de flagelle. Un faisceau dâindices semble indiquer que le SST6 formĂ© dâHcp1 serait impliquĂ© dans transport dâun ou plusieurs effecteurs agissant sur la formation des flagelles. Une deuxiĂšme partie de ces travaux de thĂšse se focalise sur dâautres propriĂ©tĂ©s spĂ©cifiques de la souche MFE01. Dâune part, la souche MFE01 ne semble pas produire de signaux de communication classiques de Quorum Sensing tout en Ă©tant capable dâadopter des comportements sociaux. Nous avons donc entrepris de vĂ©rifier cette absence de signaux de communication classiques et proposĂ© lâimplication du SST6 dans la communication. Dâautre part, nous avons collaborĂ© Ă la mise en Ă©vidence dâune action directe de la souche de MFE01 sur le dĂ©veloppement dâune plante modĂšle indĂ©pendamment du SST6 et tentĂ© dâen cerner les mĂ©canismes. Enfin, MFE01 produit des molĂ©cules volatiles organiques (VOCs) Ă action anti-Legionella. Ces travaux contribuent Ă lâĂ©tude de la production de ces VOCs par MFE01 et leurs effets sur les bactĂ©ries pathogĂšnes du genre Legionella.During this doctoral work, we focused on the specific properties of the environmental strain P. fluorescens MFE01 which is avirulent against all tested eukaryotic cells despite the presence of an extremely active T6SS. This T6SS confers to MFE01 a competitive advantage against other microorganisms. The first part of this work studies interconnections between type six secretion system (T6SS) and motility. In MFE01 genome, all needle protein-encoding hcp genes are detected outside the âcore componentâ cluster and interestingly, MFE01 seems to be able to produce different T6SS needle with specific functions depending on the incorporated Hcp protein. The Hcp1 protein is implicated in flagellar motility inhibition of target bacteria. Remarkably, the deletion of hcp1 gene inhibits MFE01 âswimmingâ ability. Our work gave some evidences that the T6SS formed by Hcp1 may secrete a least one effector targeting flagella formation. The second part of this work focuses on other specific properties of MFE01. First, MFE01 appears unable to produce classic quorum sensing signal whereas it is able to engage social behavior. We proposed a model in which T6SS may be involved in MFE01 communication. Then, we participated to highlight and understand direct activity of MFE01 on plant development by a mechanism that is independent of T6SS. Lastly, we demonstrated that MFE01 produces volatile organic compound (VOCs), which are active against Legionella. This work shows that this VOCs production is potentially under control of a global regulator and/or is involved in an undescribed regulatory network
Assemblages réversibles dirigés par liaisons hydrogÚne en solution aqueuse
De nouveaux dĂ©rivĂ©s amphiphiles, de type bis-urĂ©es, ont Ă©tĂ© synthĂ©tisĂ©s pour l'Ă©tude de leur caractĂšre auto-associatif en solution. En solvant polaire, et en particulier dans l'eau, ces amphiphiles s'organisent en objets unidirectionnels allongĂ©s, associĂ©s par liaisons hydrogĂšne et interactions hydrophobes, pour former des polymĂšres supramolĂ©culaires dynamiques, ou polymĂšres rĂ©versibles. L'auto-association dans l'eau est possible grĂące Ă la protection des liaisons hydrogĂšne Ă l'intĂ©rieur d'un micro-domaine hydrophobe. De faibles modifications de la structure chimique, typiquement un groupement mĂ©thyle, donnent des variations importantes de la viscositĂ©, et ce mĂȘme Ă faible concentration. De plus, dans l'eau, des solutions gĂ©lifiĂ©es sont obtenues autour de 60C. La forme de ces assemblages a Ă©tĂ© dĂ©terminĂ©e par diffusion de neutrons aux petits angles et cryo-microscopie : il s'agit de rubans de section elliptique dans l'eau. Des structures tubulaires n'ont pas encore Ă©tĂ© mises en Ă©vidence, mais un contrĂŽle fin de la structure supramolĂ©culaire et des propriĂ©tĂ©s d'auto-association a nĂ©anmoins Ă©tĂ© obtenu. Finalement, des molĂ©cules hydrophobes ont Ă©tĂ© ajoutĂ©es Ă des solutions aqueuses de bis-urĂ©es afin d'Ă©tudier leur influence sur les propriĂ©tĂ©s et la structure des assemblagesPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
The Type VI Secretion System: A Dynamic System for Bacterial Communication?
Numerous studies in Gram-negative bacteria have focused on the Type VISecretion Systems (T6SSs), Quorum Sensing (QS), and social behavior, such as in biofilms. These interconnected mechanisms are important for bacterial survival; T6SSs allow bacteria to battle other cells, QS is devoted to the perception of bacterial cell density, and biofilm formation is essentially controlled by QS. Here, we review data concerning T6SS dynamics and T6SSâQS cross-talk that suggest the existence of inter-bacterial communication via T6SSs
Identification of a new type 6 secretion system effector of Pseudomonas fluorescens MFE01 involved in bacterial motility inhibition
International audienc
Identification of a new type 6 secretion system effector of Pseudomonas fluorescens MFE01 involved in bacterial motility inhibition
International audienc
P. fluorescens MFE01 : Une activitĂ© PGPR dĂ©pendante du systĂšme de sĂ©crĂ©tion de type VI et dâautres mĂ©canismes.
Both Waterâ and OrganoâSoluble Supramolecular Polymer Stabilized by HydrogenâBonding and Hydrophobic Interactions
International audienceA new bis-urea based supramolecular polymer is reported and shown by viscosimetry, neutron scattering (SANS) and calorimetry (ITC) to self-assemble in a wide range of solvents, encompassing the polarity scale from water to toluene. The presence of both hydrogen bonding and hydrophobic groups ensures that self-assembly occurs in water, aprotic polar solvents or non-polar solvents. Both the driving force for the assembly and the exact structure of the filaments is solvent dependent, but whatever the solvent, long rigid filaments are formed in dynamic equilibrium with the monome