As described earlier, strain RMAST possesses similar physiological and biochemical features to species of the genus Methanothermobacter, which are hydrogenotrophic and thermophilic methanogens. Indeed, strain RMAST grew with and produced methane from H2/CO2 and had a high optimum growth temperature (70 uC). A polar lipid of strain RMAST (PNGL1) is generally found in the genera Methanothermobacter and Methanobacterium, but not in other genera (Methanobrevibacter and Methanosphaera) within the family Methanobacteriaceae (Koga et al., 1998). The 16S rRNA gene-based phylogeny (NJ and ML analyses)also revealed that strain RMAST is most closely related to members of the genus Methanothermobacter and that the 16S rRNA gene sequence similarities between strain
RMAST and the genus Methanothermobacter are higher(95.1–95.7 %) than with the genus Methanobacterium(91.3–93.8 %).