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 H₂/CO₂ and formate. Ax23^T grew on NH₄ ⁺ and by fixing N₂, but did not grow on NO₃ ^-. 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 CH₄ produced) when grown on 10 kPa H₂ relative to 160 kPa H₂, suggesting that it is capable of a metabolic trade-off with varying H₂ 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 <i>Methanococcaceae</i> in the kingdom <i>Methanobacteriati</i>. 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 <i>Methanothermococcus jasoni</i> is proposed. The type strain is Ax23^T (=DSM 118471^T=JCM39656^T).