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Aerobic methanotrophic bacteria of the genus Methylomonas inhabit a wide spectrum of habitats, including freshwater bodies, river sediments, wetlands, rice paddies, landfill cover soils, and hydromorphic soils. Majority of the currently described species of this genus are represented by neutrophilic, motile, growing on methane rod-shaped bacteria, whose pigmentation varies from yellow to pink and red. This study reports characterization of a novel, nonpigmented isolate of these bacteria, strain MW1T, which was obtained from sediments of the mountain river Khosta, Krasnodar krai, Russia. Strain MW1T grew on methane and methanol within a temperature range of 8–37°C (optimum at 25–30°C) and at рH 5.5–7.5 (optimum at 6.3–7.0). The 16S rRNA gene sequence of strain MW1T displayed 95.48–98.47% similarity to those in earlier described Methylomonas species. The closest taxonomically characterized phylogenetic relative of strain MW1T was M. fluvii EbBT, isolated from the river Elbe sediments. Complete genome sequence of strain MW1T was 4.6 Mb in size and contained three rRNA operons and about 4200 protein-encoding genes, including the gene cluster pmoCAB coding for particulate methane monooxygenase. Soluble methane monooxygenase was not encoded in the genome. The G+C DNA content was 52.4%. The average nucleotide identity of the genome of strain MW1T and the genomes of earlier described representatives of the genus Methylomonas was 79.4–82.1%. We propose to classify this isolate as representing a novel species of the genus Methylomonas, M. montana sp. nov. Strain MW1T (=VKM 3737T = UQM 41536T) is the type strain of the newly proposed species. [ABSTRACT FROM AUTHOR]

The technology of single-cell protein production from natural gas is based on using thermotolerant methanotrophic bacteria with high growth rates on methane. So far, the spectrum of strains used for industrial purposes was restricted to members of the genus Methylococcus. This poses limitations to further development of this technology and fuels the search for new cultures of fast-growing methanotrophs. The later task was addressed in the present work by analyzing the sediment samples of the Chernaya River, Crimea. Molecular analysis of the microbial community composition in the sediment revealed Gammaproteobacteria as the predominant group (33‒42% of all retrieved 16S rRNA gene fragments), as well as Chloroflexi, Actinobacteria, Alphaproteobacteria, Bacteroidota, and Acidobacteria as other numerically significant community members. The methanotrophic enrichment culture obtained from the sediment contained bacteria of the genus Methylomonas as the major component, with the relative abundance of up to 60% of all 16S rRNA gene fragments. The use of various strategies for methanotroph isolation resulted in obtaining three isolates of target bacteria of the genera Methylomonas, Methylomagnum and Methylocystis. The optimal growth temperatures of these isolates were 25, 35, and 40°С, respectively. The highest specific growth rate in batch culture, 0.21 h−1, was determined for Methylocystis sp. Kr9, which displayed 99.22 and 99.13% 16S rRNA gene sequence similarity to the type strains of two Methylocystis species, Methylocystis echinoides IMET 10491T and Methylocystis parvus OBBPT, respectively. [ABSTRACT FROM AUTHOR]