Roles of RpoN in the resistance of Campylobacter jejuni under various stress conditions

Background: Campylobacter jejuni is a leading foodborne pathogen worldwide. Despite the fastidious nature of C. jejuni growth, increasing numbers of human campylobacteriosis suggest that C. jejuni may possess unique mechanisms to survive under various stress conditions. C. jejuni possesses only three sigma factors (FliA, RpoD, and RpoN) and lacks stress-defense sigma factors. Since FliA and RpoD are dedicated to flagella synthesis and housekeeping, respectively, in this study, we investigated the role of RpoN in C. jejuni's defense against various stresses. Results: Survivability of an rpoN mutant was compared with the wild-type C. jejuni under various stress conditions. While the growth of the rpoN mutant was as comparably as that of the wild type in shaking cultures, the rpoN mutant exhibited significant survival defects when cultured statically. The rpoN mutant was more sensitive to osmotic stress (0.8% NaCl) with abnormally-elongated cell morphology. Compared to the wile type, the rpoN mutant was more susceptible to acid stress (pH 5) and more resistant to hydrogen peroxide. However, the rpoN mutation had little effect on the resistance of C. jejuni to alkaline pH, heat, cold and antimicrobials. Conclusions: The results demonstrate that RpoN plays an important role in C. jejuni's defense against various stresses which this bacterial pathogen may encounter during transmission to and infection of humans.