Methanococcoides mangrovi sp. nov. and Methanococcus mangrovi sp. nov., two novel methanogens isolated from mangrove sediments.

Two novel methanogens, designated strains FTZ1T and CFT, were isolated from mangrove sediment and from a magnetite-amended enrichment derived from the same sediment, respectively, collected from the Futian Mangrove Nature Reserve, Shenzhen, China. Strain FTZ1T utilized methanol, trimethylamine, dimethylamine, monomethylamine and glycine betaine as substrates for growth and methane production, while strain CFT grew on H2/CO2 and formate. Cells of both strains were irregular cocci, with diameters of 0.5-1.3 µm for strain FTZ1T and 0.5-1.2 µm for strain CFT. Using methanol as the substrate, strain FTZ1T grew at 20-42 °C (optimum 37 °C), pH 5.5-8.0 (optimum 7.5) and 0-0.85 M NaCl (optimum 0.34 M NaCl). Strain CFT grew at 20-45 °C (optimum 33-37 °C), pH 6.0-8.5 (optimum 7.3) and 0-0.62 M NaCl (optimum 0.10-0.21 M NaCl) when growing on H2/CO2. The genomic G+C contents are 44.4 mol% for strain FTZ1T and 33.4 mol% for strain CFT. Phylogenetic analyses showed that strain FTZ1T belongs to the genus Methanococcoides, sharing 85.20% average nucleotide identity (ANI) and 29.4% digital DNA-DNA hybridization (dDDH) with its closest relative Methanococcoides cohabitans LMO-2T. Strain CFT is assigned to the genus Methanococcus, exhibiting 88.52% ANI and 35.3% dDDH with its closest relative Methanococcus maripaludis JJT. Based on phenotypic and phylogenetic evidence, two novel species are proposed: Methanococcoides mangrovi sp. nov. (type strain FTZ1T=CCAM 1318T=JCM 39395T) and Methanococcus mangrovi sp. nov. (type strain CFT=CCAM 2191T=JCM 39555T).