Methylocystis iwaonis sp. nov., a type II methane-oxidizing bacterium from surface soil of a rice paddy field in Japan, and emended description of the genus Methylocystis ( ex Whittenbury et al . 1970) Bowman et al . 1993

A novel methane-oxidizing bacterial strain SS37A-Re T was isolated from surface soil of a rice paddy field in Japan. Cells were Gram-stain-negative, motile rods with single polar flagellum and type II intracytoplasmic membrane arrangement. The strain grew on methane or methanol as the sole carbon and energy source. It grew at 15–37 °C (optimum 25–30 °C), pH 6.0–9.0 (optimum 7.0–8.0) and with 0–0.1 % (w/w) NaCl (no growth at 0.5 % or above). Cells formed cysts, but not exospores. The results of sequence analysis of the 16S rRNA gene indicated that SS37A-Re T represented a member of the family Methylocystaceae , with the highest similarity (98.9 %) to Methylocystis parva corrig. OBBP T . Phylogenetic analysis of pmoA and mxaF genes and core genes in the genome indicated that the strain was closely related to the members of the genus Methylocystis , while the analysis of the mmoX gene indicated the close relationships with the genus Methylosinus . The values of genome relatedness between SS37A-Re T and species of the genera Methylocystis and Methylosinus were 78.6–82.5% and 21.7–24.9 % estimated by the average nucleotide identity and digital DNA–DNA hybridisation, respectively, showing the highest values with Methylocystis echinoides LMG 27198 T . The DNA G+C content was 63.2 mol% (genome). The major quinone and fatty acids were Q-8 and, C 18 : 1 (C 18 : 1 ω8 t and C 18 : 1 ω8 c ) and C 18 : 2 , respectively. On the basis of the phenotypic and phylogenetic features, the strain represents a novel species of the genus Methylocystis , for which the name Methylocystis iwaonis sp. nov. is proposed. The type strain is SS37A-Re T (=JCM 34278 T =NBRC 114996 T =KCTC 82710 T ).