Strain RMAST grew at 45–80 6C (optimum, 70 6C), at pH 5.8–8.7 (optimum,pH 6.9–7.7) and with 0.001–20 g NaCl l”1 (optimum, 2.5 g NaCl l”1). Phylogenetic analysis revealed that Methanothermobacter thermautotrophicus DHT was most closely related to the isolate (95.7% 16S rRNA gene sequence similarity).