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Dickeya dadantii: Vers la compréhension du rôle biologique des glucanes périplasmiques osmorégulés

Abstract : Osmoregulated perisplamic glucans (OPGs) are oligosaccharides accumulated in the envelope of many Gram-negative bacteria. Glucose is the sole constitutive sugar and this glucosidic backbone could be substituted by various kind of molecules depending on the species. Numerous studies indicate that these glucans belong to the common virulence factors for zoo- and phyto- pathogens Proteobacteria as Salmonella enterica or Dickeya dadantii. D. dadantii causes soft rot disease in a wide range of plant species. Strains of this species completely devoid of OPG show a pleiotropic phenotype including increased synthesis of exopolysaccharides, loss of motility, induction of a general stress response and complete loss of virulence. These phenotypes were confirmed by a proteomic analysis and suggest that strains devoid of OPGs are impaired in the perception of their environment. The link between OPGs and two component system, the main system used by bacteria to sense and respond to the environmental variation, strengthen this idea. Here we show that OPGs control the RcsCDB activation in a concentration-dependant manner, are required for proper activation of this phosphorelay by medium osmolarity, and that a high concentration of OPGs in planta is maintained to achieve the low level of activation of the RcsCDB phosphorelay required for full virulence in D. dadantii. The EnvZ-OmpR system are activated in strain devoid OPG suggesting a role of OPGs in the adaptation of osmolarity variation. The level of activation of the envelope stress system CpxAR was not affected by the loss of OPGs. These results were completed by membrane proteomic analysis and by microscopic pictures experiments but they didn't show any structural perturbation of the envelope in the strain devoid of OPGs. The study of the place of OPGs in a virulence regulatory network showed that mutation in the major virulence repressor pecS restored virulence in a D. dadantii opg-negative strain. All the phenotypes were not restored indicating that the two mutations didn't affect a same pathway. Finally, the identification of opgC was investigated, encoding a membrane-bound protein required for succinylation of OPG. However, the role of succinyl residues remains unknown.
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Submitted on : Monday, May 20, 2019 - 10:52:45 AM
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Sébastien Bontemps­-Gallo. Dickeya dadantii: Vers la compréhension du rôle biologique des glucanes périplasmiques osmorégulés. Bactériologie. Université de Lille 1, 2013. Français. ⟨tel-02133966⟩

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