sp. nov., a methanogen isolated from marine sediment near a cold seep at Four-Way Closure Ridge offshore southwestern Taiwan.

A mesophilic, hydrogenotrophic methanogen, strain FWC-SCC2, was isolated from deep-sea sediments collected by a real-time video multiple-corer at the C5-6 station near a cold seep at Four-Way Closure Ridge region during R/V Ocean Researcher III ORIII-1900 cruise in 2015. The cells were irregular cocci, non-motile and 0.8-1.2 µm in diameter. The methanogenic substrates utilized by strain FWC-SCC2 were formate or H+CO, but not acetate, methanol, ethanol or methylamines. Strain FWC-SCC2 was lysed in SDS (0.01 %, w/v). The of surface-layer protein was 116 400. The optimum growth conditions of strain FWC-SCC2 were 37 °C, 0.17 M NaCl and pH 6.7-7.0. The genomic DNA G+C content calculated from the genome sequence of strain FWC-SCC2 was 59.5 mol %. Phylogenetic analysis revealed that strain FWC-SCC2 was a member of the genus , and was most closely related to Chile 9 (97.6 % similarity of 16S rRNA gene sequence) and shared 97.4, 95.9, 95.9 and 95.4 % with GKZPZ, ML15, N2F9704 and HASU, respectively. The genome relatedness values between strain FWC-SCC2 and DSM 2702 were estimated by average nucleotide identity and digital DNA-DNA hybridization analyses and the results were 79.4 and 21.2 %, respectively. Based on the differences in physiological and biochemical properties, 16S rRNA gene phylogeny and genome relatedness presented here, it is suggested that strain FWC-SCC2 represents a novel species of the genus , and the name sp. nov. is proposed. The type strain is FWC-SCC2 (=BCRC AR10052=DSM 107935= NBRC 113164).