Methanobacterium movens sp. nov. and Methanobacterium flexile sp. nov., isolated from lake sediment.

Two mesophilic methanogenic strains, designated TS-2(T) and GH(T), were isolated from sediments of Tuosu lake and Gahai lake, respectively, in the Qaidam basin, Qinghai province, China. Cells of both isolates were rods (about 0.3-0.5×2-5 µm) with blunt rounded ends and Gram-staining-positive. Strain TS-2(T) was motile with one or two polar flagella and used only H(2)/CO(2) for growth and methanogenesis. Strain GH(T) was non-motile, used both H(2)/CO(2) and formate and displayed a variable cell arrangement depending on the substrate: long chains when growing in formate (50 mM) or under high pressure H(2) and single cells under low pressure H(2). Phylogenetic analysis based on 16S rRNA gene sequences placed the two isolates in the genus Methanobacterium. Strain TS-2(T) was most closely related to Methanobacterium alcaliphilum NBRC 105226(T) (96% 16S rRNA gene sequence similarity). Phylogenetic analysis based on the alpha subunit of methyl-coenzyme M reductase also supported the affiliation of the two isolates with the genus Methanobacterium. DNA-DNA relatedness between the isolates and M. alcaliphilum DSM 3387(T) was 39-53%. Hence we propose two novel species, Methanobacterium movens sp. nov. (type strain TS-2(T)=AS 1.5093(T)=JCM 15415(T)) and Methanobacterium flexile sp. nov. (type strain GH(T)=AS 1.5092(T)=JCM 15416(T)).