Methylacidiphilum kamchatkense gen. nov., sp. nov., an extremely acidophilic and moderately thermophilic methanotroph belonging to the phylum Verrucomicrobiota.

The thermo-acidophilic aerobic methanotrophic Verrucomicrobia bacterium, designated strain Kam1T was isolated from an acidic geothermal mud spring in Kamchatka, Russia. Kam1T is Gram-stain-negative, with non-motile cells and non-spore-forming rods, and a diameter of 0.45-0.65 µm and length of 0.8-1.0 µm. Its growth is optimal at the temperature of 55 °C (range, 37-60 °C) and pH of 2.5 (range, pH 1-6), and its maximal growth rate is ~0.11 h-1 (doubling time ~6.3 h). Its cell wall contains peptidoglycan with meso-diaminopimelic acid. In addition to growing on methane and methanol, strain Kam1T grows on acetone and 2-propanol. Phylogenetically, it forms a distinct group together with other Methylacidiphilum strains and with the candidate genus Methylacidimicrobium as a sister group. These findings support the classification of the strain Kam1T as a representative of a novel species and genus of the phylum Verrucomicrobiota. For this strain, we propose the name Methylacidiphilum kamchatkense sp. nov. as the type species within Methylacidiphilum gen. nov. Strain Kam1T (JCM 30608T=KCTC 4682T) is the type strain.