The novel gammaproteobacterial methanotroph “Ca. Methylocalor cossyra” CH1 actively coexists with verrucomicrobial methanotrophs in acidic and hot geothermal soil

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.