gen. nov., sp. nov., a methyl-reducing methanogen isolated from Shengli oil field, and proposal of fam. nov., ord. nov. and classis nov. in the phylum .

An anaerobic, thermophilic methanogen, designated strain LWZ-6, was isolated from the Shengli oil field, China. The cells of strain LWZ-6 were non-motile cocci, with a diameter of 0.5-1.0 µm, and formed aggregates. They reduced methanol and monomethylamine into methane, using H as an electron donor. Dimethylamine, trimethylamine and methanethiol, H/CO, formate, acetate, pyruvate, lactate and glucose were not used as energy sources. Strain LWZ-6 required yeast extract, acetate or CO as carbon sources. Strain LWZ-6 grew at 35-65 °C (optimum 55 °C), pH 5.0-8.0 (optimum 6.0-6.5) and 0-60 g l NaCl (optimum 9 g l). The genome was 1.54 Mbp with a G+C content of 54.42 mol%. Strain LWZ-6 shared 83.54% 16S rRNA gene sequence identity with strain 3507LT in the class . Phylogenetic analysis based on the 16S rRNA gene, along with phylogenomic analysis, indicated that strain LWZ-6 belonged to the candidate class ' Methanomethylicia', which lacks cultivated representatives. Based on these findings, a new species within a new genus, gen. nov., sp. nov., is proposed for LWZ-6 (=CCAM 1872=JCM 39528). In addition, we propose the class. nov. for candidate class '. Methanomethylicia' represented by fam. nov. and ord. nov. within the phylum .