Methanosarcina mangrovi sp. nov. and Methanosarcina sediminis sp. nov., two novel methanogenic archaea isolated from mangrove sediments.

Mangrove sediments are recognized as hotspots for methane emissions and harbour diverse methanogenic archaea. In this study, we describe two novel methanogens, strains T3T and Mfa9T, isolated from mangrove sediment samples in the Futian Mangrove Nature Reserve in Shenzhen, People's Republic of China. Cells of strains T3T and Mfa9T are irregularly coccoid in shape, with diameters of 0.7-1.4 µm and 0.6-1.7 µm, respectively. Both strains utilize methanol, methylamine, dimethylamine, trimethylamine, dimethyl sulphide and acetate as the sole carbon source for growth and methanogenesis, but not H2/CO2, formate, choline, betaine or pyruvate. Strain T3T grew at 15-42 °C (optimum 37 °C), pH 6.0-8.0 (optimum 6.5) and 0-0.72 M NaCl (optimum 0.10 M NaCl). Strain Mfa9T grew at 20-33 °C (optimum 25 °C), pH 5.5-7.5 (optimum 7.0) and 0-0.72 M NaCl (optimum 0.51 M NaCl). The genomic G+C contents of strains T3T and Mfa9T are 43.3 mol% and 46.2 mol%, respectively. Phylogenetic analyses revealed that both strains are classified within the genus Methanosarcina. Strain T3T was mostly related to Methanosarcina siciliae T4/MT, with 16S rRNA gene similarity of 99.7%, an average nucleotide identity of 88.8% and a digital DNA-DNA hybridization of 35.7%. By contrast, strain Mfa9T shared 98.8% 16S rRNA gene similarity with Methanosarcina semesiae MD1T. As M. semesiae MD1T is unavailable and lacks genomic data, comparative analyses with its closer relative Methanosarcina sp. MTP4 (99.8% 16S rRNA gene identity), together with genomic and phenotypic differences from M. semesiae, support the designation of strain Mfa9T as a novel species. In conclusion, two novel species of the genus Methanosarcina, Methanosarcina mangrovi sp. nov. and Methanosarcina sediminis sp. nov., are proposed. The type strain of M. mangrovi sp. nov. is T3T (=CCAM 2189T=JCM 39553T), and the type strain of M. sediminis sp. nov. is Mfa9T (=CCAM 2190T=JCM 39554T).