| Summary: | <p>Abstract</p> <p>Background</p> <p>The genetic features that facilitate <it>Campylobacter jejuni</it>’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 <it>C</it>. <it>jejuni</it>’s adaptation. Therefore, our objectives were to characterize the contributions of selected RPs to <it>C</it>. <it>jejuni</it>’s i- key survival phenotypes under different temperature (37°C vs. 42°C) and oxygen (microaerobic, ambient, and oxygen-limited/anaerobic) conditions and ii- its interactions with intestinal epithelial cells from disparate hosts (human vs. chickens).</p> <p>Results</p> <p><it>C</it>. <it>jejuni</it> mutant strains with individual deletions that targeted five RPs; nitrate reductase (Δ<it>napA</it>), nitrite reductase (Δ<it>nrfA</it>), formate dehydrogenase (Δ<it>fdhA</it>), hydrogenase (Δ<it>hydB</it>), and methylmenaquinol:fumarate reductase (Δ<it>mfrA</it>) were used in this study. We show that only the Δ<it>fdhA</it> exhibited a decrease in motility; however, incubation at 42°C significantly reduced the deficiency in the Δ<it>fdhA</it>’s motility as compared to 37°C. Under all tested conditions, the Δ<it>mfrA</it> showed a decreased susceptibility to hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), while the Δ<it>napA</it> and the Δ<it>fdhA</it> showed significantly increased susceptibility to the oxidant as compared to the wildtype. Further, the susceptibility of the Δ<it>napA</it> to H<sub>2</sub>O<sub>2</sub> was significantly more pronounced at 37°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 Δ<it>mfrA</it> displayed significantly deficient and increased biofilm formation under microaerobic conditions at 37°C and 42°C, respectively. However, under anaerobic conditions, the Δ<it>mfrA</it> was only significantly impaired in biofilm formation at 42°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 Δ<it>fdhA</it> and the Δ<it>hydB</it> were deficient in interacting with both cell types, while the Δ<it>mfrA</it> displayed impairments only in adherence to and invasion of INT-407. Scanning electron microscopy showed that the Δ<it>hydB</it> and the Δ<it>fdhA</it> exhibited filamentous and bulging (almost spherical) cell shapes, respectively, which might be indicative of defects in cell division.</p> <p>Conclusions</p> <p>We conclude that the RPs contribute to <it>C</it>. <it>jejuni</it>’s motility, H<sub>2</sub>O<sub>2</sub> 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 <it>C</it>. <it>jejuni</it> in a variety of niches, contributing to the pathogen’s remarkable potential for adaptation.</p>
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