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Abstract
The facultative piezophile Shewanella violacea DSS12 is known to have respiratory components that alter under the influence of hydrostatic pressure during growth, suggesting that its respiratory system is adapted to high pressure. We analyzed the expression of the genes encoding terminal oxidases and some respiratory components of DSS12 under various growth conditions. The expression of some of the genes during growth was regulated by both the O2 concentration and hydrostatic pressure. Additionally, the activities of cytochrome c oxidase and quinol oxidase of the membrane fraction of DSS12 grown under various conditions were measured under high pressure. The piezotolerance of cytochrome c oxidase activity was dependent on the O2 concentration during growth, while that of quinol oxidase was influenced by pressure during growth. The activity of quinol oxidase was more piezotolerant than that of cytochrome c oxidase under all growth conditions. Even in the membranes of the non-piezophile Shewanella amazonensis, quinol oxidase was more piezotolerant than cytochrome c oxidase, although both were highly piezosensitive as compared to the activities in DSS12. By phylogenetic analysis, piezophile-specific cytochrome c oxidase, which is also found in the genome of DSS12, was identified in piezophilic Shewanella and related genera. Our observations suggest that DSS12 constitutively expresses piezotolerant respiratory terminal oxidases, and that lower O2 concentrations and higher hydrostatic pressures induce higher piezotolerance in both types of terminal oxidases. Quinol oxidase might be the dominant terminal oxidase in high-pressure environments, while cytochrome c oxidase might also contribute. These features should contribute to adaptation of DSS12 in deep-sea environments.