The deduced amino acid sequences of mcrA of strain RMAST using the MCRf/MCRr and ME1/ME2 primer pairs were 157 and 240 amino acids long, respectively. The McrA sequence of strain RMAST exhibited high similarities with those of Methanothermobacter crinale Tm2T and Methanobacterium aarhusense H2-LRT (96.7 and 90.1 %, respectively). Very interestingly, the McrA phylogeny (Fig.2b) revealed that, despite the fact that strain RMAST and Methanothermobacter crinale Tm2T are closely related to Methanothermobacter thermautotrophicus DHT on the basis of 16S rRNA gene sequences (Fig. 2a), they were more related to members of the genus Methanobacterium than to Methanothermobacter. The reason for the discrepancy between the 16S rRNA gene and McrA phylogenies is not clear, but the physiological and biochemical features, as shown below, support the placement of strain RMAST in the genus Methanothermobacter.