A novel mesophilic, hydrogenotrophic methanogen, strain CYW5T, was isolated from a sediment sample of a piston core collected from submarine mud volcano MV5 located in the offshore area of southwestern Taiwan. Cells of strain CYW5T were irregular coccids, 0.5-1.0 µm in diameter and lysed easily by 0.01 % sodium dodecyl sulphate (SDS) treatment. Strain CYW5Tutilized formate or hydrogen plus carbon dioxide as catabolic substrates for methanogenesis. The optimal growth conditions were 37 °C, 0.043-0.085 M NaCl and pH 6.02-7.32. The genomic DNA G+C content calculated from the genome sequence of strain CYW5T was 56.2 mol%. The results of phylogenetic analysis of 16S rRNA gene sequences indicated that strain CYW5T represented a member of the family Methanomicrobiaceae in the order Methanomicrobiales, and was closely related to the members of the genus Methanogenium. The most closely related species was Methanogenium cariaci JR1T (94.9 % of 16S rRNA gene sequence identity). The average nucleotide identity and average amino acid identity values between strain CYW5T and members of the family Methanomicrobiaceae were 74.7-78.5 % and 49.1-64.9%, respectively. Although many of the morphological and physiological characteristics of strain CYW5T and the species of the genus Methanogenium were similar, they were distinguishable by the differences in genomic G+C content and temperature, NaCl and pH ranges for growth. Based on these phenotypic, phylogenetic and genomic results, we propose that strain CYW5T represents a novel species, of a novel genus, named Methanovulcanius yangii gen. nov., sp. nov. The type strain is CYW5T (=BCRC AR10048T=DSM 100756T=NBRC 111404T).
Keywords: Methanovulcanius; archaea; methanogen; submarine mud volcano.