Methanolobus mangrovi sp. nov. and Methanolobus sediminis sp. nov, two novel methylotrophic methanogens isolated from mangrove sediments in China

Two methylotrophic methanogens, designated strains FTZ2^T and FTZ6^T, were isolated from mangrove sediment sampled in Futian Mangrove Nature Reserve in Shenzhen, PR China. Cells of strains FTZ2^T and FTZ6^T were cocci, with diameters of 0.6-1.0 µm and 0.6-0.9 µm, respectively. Both strains grew on methanol, methylamine, dimethylamine and trimethylamine, but not on acetate, formate, H₂/CO₂, choline, betaine or dimethyl sulphide. Strain FTZ2^T grew at 10-37 °C (optimally at 33 °C), pH 5.5-8.0 (optimally at pH 7.0) and 0-1.03 M NaCl (optimally at 0.17 M NaCl). In contrast, strain FTZ6^T grew at 15-42 °C (optimally at 37 °C), pH 5.0-7.5 (optimally pH 6.5) and 0-1.03 M NaCl (optimally at 0.17 M NaCl). Both strains required magnesium for growth and were susceptible to sodium dodecyl sulphate. Biotin was required for the growth of strain FTZ2^T but not of strain FTZ6^T. The genomic G+C contents of strains FTZ2^T and FTZ6^T were 41.6 and 40.9 mol%, respectively. Phylogenetic analyses revealed that strain FTZ2^T was mostly related to Methanolobus psychrotolerans YSF-03^T, with 16S rRNA gene similarity of 98.6 %, an average nucleotide identity (ANI) of 82.5 %, and a digital DNA-DNA hybridization (dDDH) of 24.6 %. While strain FTZ6^T was mostly related to Methanolobus vulcani PL-12/M^T, with 16S rRNA gene similarity of 99.4 %, an ANI of 88.6% and a dDDH of 34.6 %. Based on phenotypic, phylogenetic and genotypic evidence, two novel species of the genus Methanolobus, Methanolobus mangrovi sp. nov. and Methanolobus sediminis sp. nov., are proposed. The type strain of M. mangrovi sp. nov. is FTZ2^T (=CCAM 1276^T=JCM 39396^T) and the type strain of M. sediminis sp. nov. is FTZ6^T (=CCAM 1277^T=JCM 39397^T).