Investigation of the Role of Bile Salts in the Biogenesis and Virulence of Campylobacter jejuni Outer Membrane Vesicles

Campylobacter jejuni is a leading cause of foodborne bacterial gastroenteritis worldwide. As C. jejuni lacks the classical virulence-associated secretion systems of other enteric pathogens for the delivery of effector proteins into host cells, outer membrane vesicles (OMVs) may have a particularly important role in virulence. The bile salt sodium taurocholate (ST) has previously been shown to stimulate C. jejuni OMV production and enhance pathogenic properties of OMVs through an unknown mechanism. The maintenance of lipid asymmetry (MLA) pathway has been shown to play a role in the regulation of OMV production in other bacteria. Mutation of mlaA in C. jejuni increased OMV production independent of changes to membrane stability. Additionally, OMV production of the mlaA mutant was not stimulated by ST. RNA-Seq was performed to further characterise the transcriptional responses of C. jejuni to bile salts and identify key genes as a starting point for further hypothesis driven research. The transcriptional response of C. jejuni to biologically relevant concentrations of ST and sodium deoxycholate (SDC) was investigated. The uncharacterised gene Cj0561c demonstrated the greatest transcriptional response and was selected for further investigation. C. jejuni Cj0561c mutants were constructed in two wild-type strains. Given the link between Cj0561c and the multidrug efflux pump CmeABC through the transcriptional regulator CmeR, cmeB mutant and cmeB Cj0561c double mutants were also constructed. A range of phenotypic assays were carried out but no clear function for Cj0561c was elucidated. However, Cj0561c appeared to play a role in OMV cytotoxicity and lauryl sulfobetaine sensitivity. This study furthered the knowledge of the role of bile salts in C. jejuni OMV-mediated virulence. As the gut bile composition is impacted by both diet and microbiota, this study also highlights the potential importance of diet and lifestyle factors on the varying disease presentations associated with gut pathogen infections.