Methylomagnum ishizawai gen. nov., sp nov., a mesophilic type I methanotroph isolated from rice rhizosphere

An aerobic, methane-oxidizing bacterium (strain RS11D-Pr-T) was isolated from rice rhizosphere. Cells of strain RS11D-Pr-T were Gram-stain-negative, motile rods with a single polar flagellum and contained an intracytoplasmic membrane system typical of type I methanotrophs. The strain utilized methane and methanol as sole carbon and energy sources. It could grow at 20-37 degrees C (optimum 31-33 degrees C), at pH 6.8-7.4 (range 5.5-9.0) and with 0-0.2% (w/v) NaCl (there was no growth at above 0.5% NaCl). pmoA and mmoXgenes were present. The ribulose monophosphate and/or ribulose bisphosphate pathways were used for carbon assimilation. Results of sequence analysis of 16S rRNA genes showed that strain RS11D-Pr-T is related closely to the genera Methylococcus, Methylocaldum, Methyloparacoccus and Methylogaea in the family Methylococcaceae. The similarity was low (94.6%) between strain RS11D-Pr-T and the most closely related type strain (Methyloparacoccus murrellii R-49797(T)). The DNA G+C content was 64.1 mol%. Results of phylogenetic analysis of the pmoA gene and chemotaxonomic data regarding the major cellular fatty acids (C-16:1 omega 7c, C-16 : 0 and C-14:0) and the major respiratory quinone (MC2-8) also indicated the affiliation of strain RS11D-Pr-T to the Methylococcus-Methylocaldum-Methyloparacoccus-Methylogaea clade. On the basis of phenotypic, genotypic and phylogenetic characteristics, strain RS11D-Pr-T is considered to represent a novel genus and species within the family Methylococcaceae, for which the name Methylomagnum ishizawai gen. nov., sp. nov. is proposed. The type strain is RS11D-Pr-T (=JCM 18894(T)=NBRC 109438(T)=DSM 29768(T)=KCTC 4681(T)).