A Biochemical Approach to Study the Role of the Terminal Oxidases in Aerobic Respiration in Shewanella oneidensis MR-1

The genome of the facultative anaerobic γ-proteobacterium Shewanella oneidensis MR-1 encodes for three terminal oxidases: a bd-type quinol oxidase and two heme-copper oxidases, a A-type cytochrome c oxidase and a cbb (3)-type oxidase. In this study, we used a biochemical approach and directly measured oxidase activities coupled to mass-spectrometry analysis to investigate the physiological role of the three terminal oxidases under aerobic and microaerobic conditions. Our data revealed that the cbb (3)-type oxidase is the major terminal oxidase under aerobic conditions while both cbb (3)-type and bd-type oxidases are involved in respiration at low-O(2) tensions. On the contrary, the low O(2)-affinity A-type cytochrome c oxidase was not detected in our experimental conditions even under aerobic conditions and would therefore not be required for aerobic respiration in S. oneidensis MR-1. In addition, the deduced amino acid sequence suggests that the A-type cytochrome c oxidase is a ccaa (3)-type oxidase since an uncommon extra-C terminal domain contains two c-type heme binding motifs. The particularity of the aerobic respiratory pathway and the physiological implication of the presence of a ccaa (3)-type oxidase in S. oneidensis MR-1 are discussed.