Location: Produce Safety and Microbiology ResearchTitle: The atypical hyperosmotic stress response of Campylobacter jejuni ) Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/11/2011
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The Atypical Hyperosmotic Stress Response of Campylobacter jejuni Background. Campylobacter species are unusually sensitive to hyperosmotic stress conditions imposed in the laboratory and encode no characterized osmoprotectant systems. Despite these limitations, the Gram-negative Campylobacter jejuni is prevalent, invasive, and the leading cause of bacterial food-borne diarrheal disease in the developed world. We hypothesized that C. jejuni possesses atypical molecular mechanisms for responding to hyperosmotic stress with fundamental roles in the pathogenic potential of this widespread pathogen. Methods & Results. Initial characterization of the hyperosmotic stress response revealed early adaptation but late-stage growth defects in the presence of 1.0% NaCl stress, severe filamentation of a sub-population of bacteria, and an MIC of 0.620 total osmol/L. Temporal transcriptomics of NaCl-stressed bacteria showed upregulation of heat shock proteins and enzymes for the synthesis of glutamine and glutamate, and modest, cross-protective upregulation of oxidative stress response mechanisms. Also upregulated were genes for ATP synthase (Atp) and the capsule export protein, KpsM. Interestingly, a transposon mutant screen identified mutants in 3 capsule genes (kpsM, kpsC and kpsE) with decreased osmotic tolerance. Microscopy and FACS of a GFP fusion to the atpF’ promoter showed bifurcation into GFPhigh (stress-capable) and GFPlow (non-culturable) sub-populations in the presence of NaCl. In addition, spontaneous sensitivity to hyperosmotic stress was observed in 7/50 single-colony isolates of a wild type population. This sensitivity was stable over multiple generations and was not due to “capsule-off” phase variation. Conclusion. These data have identified atypical stress management and survival tactics in an organism that lacks many hallmark response and virulence factors. The role of heat shock proteins and the capsule have clear significance for colonization of susceptible hosts. These studies also implicate novel genetic mechanisms underlying C. jejuni population heterogeneity, which may reflect an important “bet-hedging” stress-survival mechanism.