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

## TL;DR

A new heat-loving methane-producing microbe was discovered in deep-sea hydrothermal vents and named Methanothermococcus jasoni.

## Contribution

The discovery and characterization of a novel thermophilic methanogen species from subseafloor hydrothermal vent fluids.

## Key findings

- The isolate grows optimally at 73 °C and 3–4.5% NaCl with a minimum doubling time of 32 min.
- The genome of Ax23T was sequenced, revealing a 1,662,948 bp chromosome and a 7,732 bp plasmid.
- Phylogenetic analysis shows it is closely related to other Methanococcaceae species but distinct enough to be a new species.

## Abstract

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).