Methanosarcina subterranea sp. nov., a methanogenic archaeon isolated from a deep subsurface diatomaceous shale formation

A methanogenic archaeon, strain HC-2 ᵀ, was isolated from a deep diatomaceous shale formation. The strain grew on methanol, monomethylamine, dimethylamine, trimethylamine and dimethylsulphide, but not on acetate, H ₂/CO ₂, formate, 2-propanol, 2-butanol or cyclopentanol. Cells were Gram-stain-negative, non-motile, and coccus-like, 0.9–1.4 µm in diameter, and occurred singly, in pairs, or as aggregates. The strain grew at 10–40 °C (optimum 35 °C), pH 5.9–7.4 (optimum pH 6.6–6.8) and in 0–0.6 M NaCl (optimum 0.1–0.2 M). The genomic DNA G+C content was 41.5 mol% and the 16S rRNA gene sequence was closely related to those of Methanosarcina lacustris DSM 13486 ᵀ (99.1 %) and Methanosarcina siciliae DSM 3028 ᵀ (98.3 %). Values for DNA–DNA hybridization with these strains were less than 30 %. The phenotypic and phylogenetic features of HC-2 ᵀ indicate that it represents a novel species of the genus Methanosarcina , for which the name Methanosarcina subterranea sp. nov. is proposed. The type strain is HC-2 ᵀ (= DSM 22503 ᵀ = JCM 15540 ᵀ = NBRC 102578 ᵀ).