Methylococcus magnus sp. nov., a Novel Halo- and Thermotolerant Methanotroph from a Landfill Cover Soil

Abstract

The genus Methylococcus is represented by obligately aerobic gram-negative cocci and diplococci, which utilize methane as a source of carbon and energy. These bacteria inhabit a wide spectrum of habitats with high methane availability. Vast majority of the currently characterized members of this genus are thermotolerant microorganisms with high sensitivity to NaCl. Here, we report description of the first halotolerant Methylococcus representative, strain Мс7T, which was isolated from a landfill cover soil. Cells of this strain (1.6 µm in size) were larger than those of earlier described Methylococcus species (~1 µm) and grew in the temperature range 28–53°C with the optimum at 40°C and рН 5.5–7.5 with the optimum at рН 6.5–7.0. The tolerance of strain Мс7T to NaCl (1.5%, wt/vol) exceeded that in other Methylococcus spp. This methanotroph demonstrated growth in the medium with the total salt content of up to 25 g L–1. The 16S rRNA gene sequence of strain Мс7T displayed highest similarity (98.56%) to that of M. geothermalis IM1T. The finished genome sequence of strain Мс7T was 4.0 Mbp in size and contained 2 rrn operons, about 3700 protein-encoding genes including 2 copies of gene clusters of particulate methane monooxygenase (MMO) and one gene cluster of soluble MMO. The G + C DNA content was 63.44%. The average nucleotide identity between the genome sequences of strain Мс7T and M. geothermalis IM1T was 88.56%. Based on the number of phenotypic and genotypic differences we propose to classify strain Мс7T (=VKM B-4034T) as representing a novel species of the genus Methylococcus, M. magnus.