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

Two novel methanogens, designated strains FTZ1^T and CF^T, 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 FTZ1^T utilized methanol, trimethylamine, dimethylamine, monomethylamine and glycine betaine as substrates for growth and methane production, while strain CF^T grew on H₂/CO₂ and formate. Cells of both strains were irregular cocci, with diameters of 0.5-1.3 µm for strain FTZ1^T and 0.5-1.2 µm for strain CF^T. Using methanol as the substrate, strain FTZ1^T 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 CF^T 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 FTZ1^T and 33.4 mol% for strain CF^T. Phylogenetic analyses showed that strain FTZ1^T 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-2^T. Strain CF^T is assigned to the genus Methanococcus, exhibiting 88.52% ANI and 35.3% dDDH with its closest relative Methanococcus maripaludis JJ^T. Based on phenotypic and phylogenetic evidence, two novel species are proposed: Methanococcoides mangrovi sp. nov. (type strain FTZ1^T=CCAM 1318^T=JCM 39395^T) and Methanococcus mangrovi sp. nov. (type strain CF^T=CCAM 2191^T=JCM 39555^T).