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

Abstract

An aerobic, methane-oxidizing bacterium (strain RS11D-PrT) was isolated from rice rhizosphere. Cells of strain RS11 D-PrT 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 °C (optimum 31 -33 °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 RS11 D-PrT is related closely to the genera Methylococcus, Methylocaldum, Methyloparacoccus and Methylogaea in the family Methylococcaceae.The similarity was low (94.6%) between strain RS11 D-PrT and the most closely related type strain (Methyloparacoccus murrellii R-49797T). 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 (C16:1ω7c,C16:0 and C14:0) and the major respiratory quinone (MQ-8) also indicated the affiliation of strain RS11 D-PrT to the Methylococcus-Methylocaldum-Methyloparacoccus-Methylogaea clade. On the basis of phenotypic, genotypic and phylogenetic characteristics, strain RS11 D-PrT 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-PrT (=JCM 1 8894T=NBRC 1 09438T=DSM 29768T=KCTC 4681T).