Methylosoma difficile gen. nov., sp. nov., a novel methanotroph enriched by gradient cultivation from littoral sediment of Lake Constance

Abstract

A novel methanotroph, strain LC 2^T, was isolated from the littoral sediment of Lake Constance by enrichment in opposing gradients of methane and oxygen, followed by traditional isolation methods. Strain LC 2^T grows on methane or methanol as its sole carbon and energy source. It is a Gram-negative, non-motile, pale-pink-coloured methanotroph showing typical intracytoplasmic membranes arranged in stacks. Cells are coccoid, elliptical or rod-shaped and occur often in pairs. Strain LC 2^T grows at low oxygen concentrations and in counter-gradients of methane and oxygen. It can grow on medium free of bound nitrogen, possesses the nifH gene and fixes atmospheric nitrogen at low oxygen pressure. It grows at neutral pH and at temperatures between 10 and 30 °C. Phylogenetically, it is most closely related to the genus Methylobacter, with the type strains of Methylobacter tundripaludum and Methylobacter psychrophilus showing 94 and 93.4 % 16S rRNA gene sequence similarity, respectively. Furthermore, the pmoA gene sequence of strain LC 2^T is most closely related to pmoA gene sequences of Methylobacter strains (92 % similar to Methylobacter sp. LW 12 by deduced amino acid sequence identity). The DNA G+C content is 49.9 mol% and the major cellular fatty acid is 16 : 1ω7c (60 %). Strain LC 2^T (=JCM 14076^T=DSM 18750^T) is described as the type strain of a novel species within a new genus, Methylosoma difficile gen. nov., sp. nov.