gen. nov., sp. nov., a thermoacidophilic methane-oxidizing bacterium from an acidic geothermal environment, and descriptions of the family fam. nov. and order ord. nov.

Strain IT6, a thermoacidophilic and facultative methane-oxidizing bacterium, was isolated from a mud-water mixture collected from Pisciarelli hot spring in Pozzuoli, Italy. The novel strain is white when grown in liquid or solid media and forms Gram-negative rod-shaped, non-flagellated, non-motile cells. It conserves energy by aerobically oxidizing methane and hydrogen while deriving carbon from carbon dioxide fixation. Strain IT6 had three complete operons encoding particulate methane monooxygenase and genes encoding group 1d and 3b [NiFe] hydrogenases. Simple carbon-carbon substrates such as ethanol, 2-propanol, acetone, acetol and propane-1,2-diol were used as alternative electron donors and carbon sources. Optimal growth occurred at 50-55°C and between pH 2.0-3.0. The major fatty acids were C, C anteiso, C iso, C and C, and the main polar lipids were phosphatidylethanolamine, aminophospholipid, phosphatidylglycerol, diphosphatidylglycerol, some unidentified phospholipids and glycolipids, and other unknown polar lipids. Strain IT6 has a genome size of 2.19 Mbp and a G+C content of 40.70 mol%. Relative evolutionary divergence using 120 conserved single-copy marker genes (bac120) and phylogenetic analyses based on bac120 and 16S rRNA gene sequences showed that strain IT6 is affiliated with members of the proposed order '' of the class in the phylum . It shared a 16S rRNA gene sequence identity of >96 % with cultivated isolates in the genus '' of the family '', which are thermoacidophilic methane-oxidizing bacteria. ' sp.' Phi (100 %), ' V4 (99.02 %) and ' sp.' RTK17.1 (99.02 %) were its closest relatives. Its physiological and genomic properties were consistent with those of other isolated '' species. Based on these results, we propose the name gen. nov., sp. nov. to accommodate strain IT6 (=KCTC 92103=JCM 39288). We also formally propose that the names fam. nov. and ord. nov. to accommodate the genus gen. nov.