Methylococcus geothermalis sp. nov., a methanotroph isolated from a geothermal field in the Republic of Korea

Abstract

A Gram-stain-negative, aerobic, non-motile and coccoid methanotroph, strain IM1 T , was isolated from hot spring soil. Cells of strain IM1 T were catalase-negative, oxidase-positive and displayed a characteristic intracytoplasmic membrane arrangement of type I methanotrophs. The strain possessed genes encoding both membrane-bound and soluble methane monooxygenases and grew only on methane or methanol. The strain was capable of growth at temperatures between 15 and 48 °C (optimum, 30–45 °C) and pH values between pH 4.8 and 8.2 (optimum, pH 6.2–7.0). Based on phylogenetic analysis of 16S rRNA gene and PmoA sequences, strain IM1 T was demonstrated to be affiliated to the genus Methylococcus . The 16S rRNA gene sequence of this strain was most closely related to the sequences of an uncultured bacterium clone FD09 (100 %) and a partially described cultured Methylococcus sp. GDS2.4 (99.78 %). The most closely related taxonomically described strains were Methylococcus capsulatus Texas T (97.92 %), Methylococcus capsulatus Bath (97.86 %) and Methyloterricola oryzae 73a T (94.21 %). Strain IM1 T shared average nucleotide identity values of 85.93 and 85.62 % with Methylococcus capsulatus strains Texas T and Bath, respectively. The digital DNA–DNA hybridization value with the closest type strain was 29.90 %. The DNA G+C content of strain IM1 T was 63.3 mol% and the major cellular fatty acids were C 16 : 0 (39.0 %), C 16 : 1 ω 7 c (24.0 %), C 16 : 1 ω 6 c (13.6 %) and C 16 : 1 ω 5 c (12.0 %). The major ubiquinone was methylene-ubiquinone-8. On the basis of phenotypic, genetic and phylogenetic data, strain IM1 T represents a novel species of the genus Methylococcus for which the name Methylococcus geothermalis sp. nov. is proposed, with strain IM1 T (=JCM 33941 T =KCTC 72677 T ) as the type strain.

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