Methylocapsa polymorpha sp. nov., a Novel Dinitrogen-Fixing Methanotroph from a Subarctic Wetland

Abstract

A novel isolate of aerobic, mildly acidophilic methanotrophic bacteria, strain RX1^T, was obtained from a subarctic Sphagnum peat bog in European Russia. Strain RX1^T was represented by highly polymorphic, gram-negative, non-motile, encapsulated cells that possessed a particulate methane monooxygenase enzyme and grew on methane, methanol and acetate. Electron microscopy of ultrathin cell sections revealed stacks of intracytoplasmic membrane vesicles located on one side of a cell as characteristic for methanotrophs of the genus Methylocapsa. Strain RX1^T was capable of fixing dinitrogen, belonged to the family Beijerinckiaceae, and was most closely related to the obligate methanotroph Methylocapsa acidiphila B2^T (98.8% 16S rRNA gene sequence similarity and 92.2% of PmoA sequence identity). The genome of strain RX1^T consisted of a 4.02 Mb chromosome and a 291 kb plasmid, and contained one rrn operon, one pmoCAB operon and about 3800 protein-coding genes. The average nucleotide identity between the genomes of strain RX1^T and M. acidiphila B2^T was 80.0%. Based on the distinct cell morphology, phenotypic and genotypic differences between strain RX^T and earlier described members of the genus Methylocapsa, we propose to classify it as representing a novel species of this genus, M. polymorpha, with the type strain RX1^T = VKM B-3754^T = UQM 41806^T.