Project description:Brucellosis is a zoonosis of the Mediterranean and Middle-East regions linked to important economic losses and reduced animal welfare. To date, no effective diagnostic and/or prophylactic measures are available for the control of brucellosis, due to the residual virulence of the bacterial strain administered for vaccinal purposes and the difficulties in distinguishing vaccinated from infected animals. To overcome these issues, studies are desired to elucidate the bacterial biology and the pathogenetic mechanisms of both the vaccinal strain and the pathogenic strains. Here, we employed a label-free shotgun proteomics to investigate the protein repertoire of the vaccinal strain B. melitensis Rev.1 and compare it with the proteome of the Brucella melitensis 16 M, one of the most common field strains isolated from ruminants. Comparative proteomics profiling underlines common and diverging traits between the two strains, providing suggestions on the potential biochemical routes responsible of the residual virulence of the vaccinal strain; whilst the diverging traits are suggestive biochemical signatures to be further investigated to provide an optimized diagnostics capable of discriminating the vaccinated from infected animals.
Project description:Many pathogenic bacteria use a regulatory process termed Quorum Sensing (QS) to produce and detect small diffusible molecules to synchronize gene expression within a population. In Gram-negative bacteria, the detection and response to these molecules depend on transcriptional regulators belonging to the LuxR family. Such a system have been discovered in the intracellular pathogen Brucella melitensis, a Gram-negative bacteria responsible for brucellosis, a word-wide zoonosis remaining a serious public health concern in endemic countries. Two LuxR-type regulators, VjbR and BabR, have been identified in the genome of this pathogen. The vjbR mutant is highly attenuated in all tested models suggesting a crucial role of QS in the virulence of Brucella. This attenuation is at least due to the involvement of VjbR in the activation of the virB operon coding for a type four secretion system essential for Brucella to reach its intracellular replication compartment. At present, no function has been attributed to BabR. To assess the role of both Brucella QS-regulators, we performed in tandem comparative transcriptomic and proteomic analyses of vjbR and babR mutants. These experiments revealed that 10% of Brucella genome is regulated through those regulators, revealing that QS is a global regulatory system in this intracellular pathogen. The overlapping between BabR and VjbR targets suggest an unexpected cross-talk between these two regulators. Moreover, our results demonstrate that VjbR and BabR regulate many gene and/or proteins involved in stress response, metabolism and virulence. These targets are potentially involved in the adaptation of Brucella to the oxidative, pH and nutritional stresses encountered within the host. These findings highlight the involvement of QS in the virulence of Brucella and led us to suggest that this regulatory system could be implied in the spatial and sequential adaptation of Brucella to the host environment. Keywords: Quorum Sensing, Comparative gene expression, Brucella melitensis