Adaptation and stress response rely on the coordination of several molecular actors involved in stimuli perception, signal integration or the establishment of the adaptative response. In pathogenic bacteria, the regulatory mechanisms are essential to ensure an successful infectious process. Under certain conditons, the response of the bacteria leads to biofilm formation which are often associated with resistance mechanisms. During its lifetime, B. melitensis might be facing changing environmental conditions sometimes harmful. Mutants altered in Quorum Sensing system form bacterial clusters structurally similar to biofilms. The study of these aggregates revealed that they were predominantly composed of exopolysaccharide (EPS). However, the conditions under which this EPS is produced by the wild type bacterium, its role and the genes encoding the enzymes responsible for its biosynthesis remained unknown. In this study, we demonstrated the formation of aggregates in response to salt stress by wild type Brucella spp. We showed that the formation of these bacterial clumps depends on the presence of a phosphorelay PrlS/PrlR and of the ionic strength of the growth medium. Our data, however, challenged the exitence of a production of an exopolysaccharide by Brucella spp. Finally, we studied the role of two regulators, the system PrlS/PrlR and the transcriptional regulator MucR in the formation of aggregates in response to salt stress and in the virulence of B. melitensis. Our data indicate that the system PrlS/PrlR, required for persistent infection in vivo, is involved in the response to salt stress and regulate actors probably required for aggregation. Moreover, MucR is a key regulator of stress response and is involved in intracellular survival of the bacteria. We showed that it acts as a repressor of flagellar gene expression and is required for growth of B. melitensis in hypersaline conditions. If MucR involvement in the regulation of EPS remains to be shown in B. melitensis, our data shows its role in the regulation of the structure of another major component of the bacterial surface, the lipopolysaccharide.
Corrélation entre la réponse au stress et la virulence : implication des régulateurs transcriptionnels PrlR et MucR chez la bactérie pathogène Brucella melitensis
Mirabella, A. (Author). 19 Jul 2012
Student thesis: Doc types › Doctor of Sciences