Methanothermococcus jasoni sp. nov., a novel thermophilic methanogen from subseafloor hydrothermal vent fluids of Axial Seamount, Juan de Fuca Ridge

Low-temperature (34 °C) hydrothermal fluid was collected from Axial Seamount along the Juan de Fuca Ridge in the northeast Pacific Ocean. A thermophilic methanogen, designated strain Ax23 T , was isolated from this fluid. The archaeon was anaerobic, autotrophic and coccoidal and grew separately on H 2 /CO 2 and formate. Ax23 T grew on NH 4 + and by fixing N 2 , but did not grow on NO 3 - . The isolate grew at temperatures ranging from 33 to 75 °C (optimum 73 °C) and a minimum doubling time of 32 min, in the presence of 3–6% NaCl (optimum 3–4.5%) and pH 4.0–9.0 (optimum 6.0–8.0). It increased its growth yield (cells produced per mole of CH 4 produced) when grown on 10 kPa H 2 relative to 160 kPa H 2 , suggesting that it is capable of a metabolic trade-off with varying H 2 availability. Phylogenetic analysis based on 16S rRNA gene sequence indicated that the strain was 95.6–99.7% identical to other thermophilic species of the family Methanococcaceae in the kingdom Methanobacteriati . The complete genome of Ax23 T was sequenced, which yielded a 1,662,948 bp chromosome with 1,663 protein-coding sequences and a 7,732 bp plasmid. Based on genome-relatedness index analyses and its phenotypic characteristics, strain Ax23 T represents a novel species, for which the name Methanothermococcus jasoni is proposed. The type strain is Ax23 T (=DSM 118471 T =JCM39656 T ).