Abstract
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-O2 tensions. On the contrary, the low O2-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.
Highlights
In the oxygen respiratory systems, electrons of low-redox potential electron donors are transferred through a series of membrane-bound proteins or complexes and the reduction of molecular oxygen to water is catalyzed by enzymes called terminal oxidases
Doubling time of the strain containing only the bd-type oxidase (SLL06) was significantly longer and the growth yield lower than those of the wild-type strain, with values similar to those of the single oxidase mutants lacking cbb3-type oxidase (SLL01). It was not possible, despite numerous efforts, to generate a double oxidase mutant lacking both bd-type and cbb3-type oxidases suggesting that this mutant was not viable under aerobic conditions. These results demonstrate that the cbb3-type or the bd-type oxidase is required for aerobic growth of S. oneidensis MR-1 and that the cbb3-type terminal oxidase is the major oxidase in exponentially growing cells
We investigated the aerobic respiratory pathway in S. oneidensis MR-1 to determine the physiological role of the three terminal oxidases in low and in high-O2 environments
Summary
In the oxygen respiratory systems, electrons of low-redox potential electron donors are transferred through a series of membrane-bound proteins or complexes and the reduction of molecular oxygen to water is catalyzed by enzymes called terminal oxidases. These oxygen reductases are complicated integral membrane multi-subunit complexes grouped into two major superfamilies. Marritt et al [24] hypothesized that, in accordance with their predicted affinity for molecular oxygen, S. oneidensis MR-1 A-type and C-type cytochrome c oxidases should operate under aerobic and microaerobic conditions respectively. A thorough comparison between our results and those obtained by Zhou and colleagues [25] is developed in the discussion section
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