gen. nov., sp. nov., the first oceanic methanogen, isolated from potential methane hydrate bearing area offshore southwestern Taiwan.

A novel mesophilic, hydrogenotrophic methanogen, strain CWC-04, was obtained from a sediment sample extracted from a gravity core retrieved at station 22 within the KP-9 area off the southwestern coast of Taiwan during the ORIII-1368 cruise in 2009. Cells of strain CWC-04 were rod-shaped, 1.4-2.9 µm long by 0.5-0.6 µm wide, and occurred singly. Strain CWC-04utilized formate, H/CO, 2-propanol/CO or 2-butanol/CO as catabolic substrates. The optimal growth conditions were 42 °C, 0.17 M NaCl and pH 5.35. The genomic DNA G+C content calculated from the genome sequence of strain CWC-04 was 46.19 mol%. Phylogenetic analysis of 16S rRNA gene revealed that strain CWC-04 is affiliated with the genus . The 16S rRNA gene sequences similarities within strains MRE50, SANAE and HZ254 were 93.7, 93.0 and 91.3 %, respectively. In addition, the optical density of CWC-04 culture dropped abruptly upon entering the late-log growth phase, with virus-like particles (150 nm in diameter) being observed on and around the cells. This observation suggests that strain CWC-04 harbours a lytic virus. Based on these phenotypic, phylogenetic and genomic results, we propose that strain CWC-04 represents a novel species of a novel genus in the family , for which the name gen. nov., sp. nov. is proposed. The type strain is CWC-04 (=BCRC AR10050=NBRC 113165).