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 Ax23T, was isolated from this fluid. The archaeon was anaerobic, autotrophic and coccoidal and grew separately on H2/CO2 and formate. Ax23T 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 Methanococcaceae in the kingdom Methanobacteriati. The complete genome of Ax23T 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 Ax23T represents a novel species, for which the name Methanothermococcus jasoni is proposed. The type strain is Ax23T (=DSM 118471T=JCM39656T).
Rizzo et al. (Tue,) studied this question.