The phylogenetic analysis based on 16S rRNA gene sequences revealed that strain RMAST was a member of the genus Methanothermobacter within the family Methanobacteriaceae(Fig. 2a). This relationship was supported by high bootstrap values (100%) obtained by the neighbour-joining and maximum-likelihood methods, but not by the maximumparsimony method. Nonetheless, strain RMAST showed high sequence similarities with members of the genus Methanothermobacter with validly published names, e.g. Methanothermobacter thermautotrophicus DHT (95.7% 16S rRNA gene sequence similarity), Methanothermobacter thermoflexus IDZT (95.6%)