Oxidative phosphorylation in a thermophilic, facultative chemoautotroph,Hydrogenophilus thermoluteolus, living prevalently in geothermal niches

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is a thermophilic, facultative chemoautotroph, which lives prevalently in high temperature geothermal niches. Despite the environmental distribution, little is known about its oxidative phosphorylation. Here, we show that inverted membrane vesicles derived fromHydrogenophilus thermoluteoluscells autotrophically cultivated with H2 formed a proton gradient on the addition of succinate, dl-lactate, and NADH, and exhibited oxidation activity toward these three organic compounds. These indicate the capability of mixotrophic growth of this bacterium. Biochemical analysis demonstrated that the same vesicles contained an F-type ATP synthase. The F1 sector of the ATP synthase purified fromH. thermoluteolusmembranes exhibited optimal ATPase activity at 65°C. TransformedEscherichia colimembranes expressingH. thermoluteolusF-type ATP synthase exhibited the same temperature optimum for the ATPase. These findings shed light onH. thermoluteolusoxidative phosphorylation from the aspects of membrane bioenergetics and ATPase biochemistry, which must be fundamental and advantageous in the biogeochemical cycles occurred in the high temperature geothermal niches.

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