This work has studied several aspects of the physiology of the animal-colonizing species Campylobacterjejuni, Helicobacter pylori. Wolinella succinogenes and Arcobacter butzleri. C. jejuni and H pylori were found to be obligate microaerophiles and W.succinogenes an anaerobe. A. butzleri was found to be an aerobe able to grow anaerobically. Comparative analyses of the responses of C. jejuni, H pylori and W. succinogenes to various oxygen concentrations were investigated using transcriptomics and genes differentially expressed at higher oxygen concentrations were identified. At the time of this study no microarrays were available for A. butzleri. These comparative studies provided a better understanding of bacterial adaptation to and interaction with their environment. Several enzymes involved in oxireduction processes, including disulfide reductases, were upregulated under oxidative stress. Disulfide reductases of host-colonizing bacteria are involved in the expression of virulence factors, resistance to drugs, and elimination of toxic compounds. CXXC and CXXC-derived motifs are present in the active sites of disulfide reductases and are essential for the catalysis of these redox reactions. Large-scale genome analyses of 281 prokaryotes identified CXXC and CXXC-derived motifs in each microorganism. The total number of these motifs showed correlations with genome size and oxygen tolerance of the prokaryotes. Specific bioinformatic analyses served to identify putative disulfide reductases in the four Campylobacterales species. The project investigated the involvement of these enzymes in resistance to the antibiotic metronidazole, cadmium detoxication and pathogenesis. The activities of disulfide reductases were modulated by the presence of metronidazole, and its reduction was inhibited by the presence of disulfide reductase substrates. In addition, proteins involved in oxireduction of the low redox potential ferredoxin were downregulated in metronidazole resistant strains, suggesting that ferredoxin is involved in the resistant phenotype. Cellular processes and pathways regulated under cadmium stress included fatty acid biosynthesis, protein biosynthesis, chemotaxis and mobility, the tricarboxylic acid cycle, protein modification, redox processes and heat shock response. Notably, the data provided evidence for a role of oxireduction processes in the development of metronidazole resistance and the detoxication of cadmium. Furthermore, a method was developed to identify thiol disulfide oxidoreductases in the four Campylobacterales. The results suggested that H pylori contained a novel disulfide bond formation system. Investigation of their potential involvement in virulence or colonization indicated that the putative thiol disulfide oxidoreductases HP0231 and HP0595 are related to the colonization efficiency ofH pylori. Finally, the only known disulfide reduction system in Campylobacterales, the thioredoxin system, was investigated in more detail. Phylogenetic analyses of the thioredoxin reductases TrxB1 and TrxB2 of the four bacteria were performed. The phylogenetic features of the TrxB2 suggested a special role for this enzyme in the physiology of these bacteria; thus, the enzyme was investigated further in H pylori. TrxB2 was found to be an NADPH reductase, possibly involved in important oxireduction processes within the cell.