Terrestrial geothermal ecosystems are habitats typically characterized by large emissions of environmentally relevant gases. These emissions include CO2, CH4, H2S and H2, providing a niche for chemolithoautotrophic microorganisms. Here, we report on the isolation and characterization of a novel thermophilic and acid-tolerant gammaproteobacterial methanotroph of the family Methylococcaceae, isolated from the Favara Grande. The isolate represents a novel species and genus growing at pH values ranging from 3.5 to 7.0 (pHopt = 6.0) and a temperature range of 35 to 55 °C (Topt = 50 °C). This diazotrophic methanotroph possesses genes encoding the particulate and soluble methane monooxygenases pMMO and sMMO, together with genes encoding the lanthanide-dependent and calcium-dependent methanol dehydrogenases XoxF and MxaF. The genome of the strain CH1 encodes the enzymes of the complete Calvin cycle and of a group 3d [NiFe] hydrogenase, coupling H2 oxidation to the production of NAD(P)H or reverse. However, strain CH1 did not show autotrophic/mixotrophic growth on H2 and CO2. In addition, it possesses three different types of sulfide:quinone oxidoreductases (SQRs, type I, II and III), indicating the possibility of H2S oxidation. For this novel species we propose the name “Candidatus Methylocalor cossyra” CH1.
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