Respiratory proteins contribute differentially to Campylobacter jejuni's survival and in vitro interaction with hosts' intestinal cells

Background: The genetic features that facilitate Campylobacter jejuni's adaptation to a wide range of environments are not completely defined. However, whole genome expression studies showed that respiratory proteins (RPs) were differentially expressed under varying conditions and stresses, suggesting further unidentified roles for RPs in C. jejuni's adaptation. Therefore, our objectives were to characterize the contributions of selected RPs to C. jejuni's i-key survival phenotypes under different temperature (37 degrees C vs. 42 degrees C) and oxygen (microaerobic, ambient, and oxygen-limited/anaerobic) conditions and ii-its interactions with intestinal epithelial cells from disparate hosts (human vs. chickens). Results: C. jejuni mutant strains with individual deletions that targeted five RPs; nitrate reductase (Delta napA), nitrite reductase (Delta nrfA), formate dehydrogenase (Delta fdhA), hydrogenase (Delta hydB), and methylmenaquinol: fumarate reductase (Delta mfrA) were used in this study. We show that only the Delta fdhA exhibited a decrease in motility; however, incubation at 42 degrees C significantly reduced the deficiency in the Delta fdhA's motility as compared to 37 degrees C. Under all tested conditions, the Delta mfrA showed a decreased susceptibility to hydrogen peroxide (H2O2), while the Delta napA and the Delta fdhA showed significantly increased susceptibility to the oxidant as compared to the wildtype. Further, the susceptibility of the Delta napA to H2O2 was significantly more pronounced at 37 degrees C. The biofilm formation capability of individual RP mutants varied as compared to the wildtype. However, the impact of the deletion of certain RPs affected biofilm formation in a manner that was dependent on temperature and/or oxygen concentration. For example, the Delta mfrA displayed significantly deficient and increased biofilm formation under microaerobic conditions at 37 degrees C and 42 degrees C, respectively. However, under anaerobic conditions, the Delta mfrA was only significantly impaired in biofilm formation at 42 degrees C. Additionally, the RPs mutants showed differential ability for infecting and surviving in human intestinal cell lines (INT-407) and primary chicken intestinal epithelial cells, respectively. Notably, the Delta fdhA and the Delta hydB were deficient in interacting with both cell types, while the Delta mfrA displayed impairments only in adherence to and invasion of INT-407. Scanning electron microscopy showed that the Delta hydB and the Delta fdhA exhibited filamentous and bulging (almost spherical) cell shapes, respectively, which might be indicative of defects in cell division. Conclusions: We conclude that the RPs contribute to C. jejuni's motility, H2O2 resistance, biofilm formation, and in vitro interactions with hosts' intestinal cells. Further, the impact of certain RPs varied in response to incubation temperature and/or oxygen concentration. Therefore, RPs may facilitate the prevalence of C. jejuni in a variety of niches, contributing to the pathogen's remarkable potential for adaptation.