Methylomonas defluvii sp. nov., a type I methane-oxidizing bacterium from a secondary sedimentation tank of a wastewater treatment plant

An aerobic methanotroph was isolated from a secondary sedimentation tank of a wastewater treatment plant and designated strain OY6 T . Cells of OY6 T were Gram-stain-negative, pink-pigmented, motile rods and contained an intracytoplasmic membrane structure typical of type I methanotrophs. OY6 T could grow at a pH range of 4.5–7.5 (optimum pH 6.5) and at temperatures ranging from 20 °C to 37 °C (optimum 30 °C). The major cellular fatty acids were C 14 : 0 , C 16 : 1 ω7 c /C 16 : 1 ω6 c and C 16 : 1 ω5 c ; the predominant respiratory quinone was MQ-8. The genome size was 5.41 Mbp with a DNA G+C content of 51.7 mol%. OY6 T represents a member of the family Methylococcaceae of the class Gammaproteobacteria and displayed 95.74–99.64 % 16S rRNA gene sequence similarity to the type strains of species of the genus Methylomonas . Whole-genome comparisons based on average nucleotide identity (ANI) and digital DNA–DNA hybridisation (dDDH) confirmed that OY6 T should be classified as representing a novel species. The most closely related type strain was Methylomonas fluvii EbB T , with 16S rRNA gene sequence similarity, ANI by blast (ANIb), ANI by MUMmer (ANIm) and dDDH values of 99.64, 90.46, 91.92 and 44.5 %, respectively. OY6 T possessed genes encoding both the particulate methane monooxygenase enzyme and the soluble methane monooxygenase enzyme. It grew only on methane or methanol as carbon sources. On the basis of phenotypic, genetic and phylogenetic data, strain OY6 T represents a novel species within the genus Methylomonas for which the name Methylomonas defluvii sp. nov. is proposed, with strain OY6 T (=GDMCC 1.4114 T =KCTC 8159 T =LMG 33371 T ) as the type strain.