Genomic Determinants of Phototrophy in Methanotrophic Alphaproteobacteria

Abstract

Aerobic methanotrophic bacteria are an ecologically important group of microorganisms, which are functionally specialized in oxidation of the greenhouse gas methane. Recent insights into the growing pool of available genome sequences from methanotrophs revealed a number of as-yet-unknown metabolic capabilities of these bacteria. Thus, the genes indicative of aerobic anoxygenic photosynthesis by means of the photosystem II characteristic of purple bacteria were revealed in the genome of an obligate methanotroph Methylocapsa palsarum NE2^T. Advanced search for genomic determinants of phototrophy in other methanotrophs confirmed their occurrence in a number of methanotrophic Alphaproteobacteria, including Methylocella silvestris BL2^T and TVC, Methylocystis rosea SV97^T and GW6, as well as Methylocystis spp. strains SB2 and MitZ-2018. Genomes of these methanotrophs contained the pufABCLM gene clusters encoding the light-harvesting complex, bch/chl genes responsible for bacteriochlorophyll biosynthesis, and the pucC gene essential for bacteriochlorophyll transport, as well as the crtFDC, crtL and crtB genes responsible for carotenoid biosynthesis. Organization of these gene clusters was conserved within each methanotroph species and was highly similar in Methylocapsa and Methylocella strains. A number of rearrangements, including inverse localization of the genes encoding bacteriochlorophyll and carotenoid biosynthesis, were observed in the genomes of Methylocystis species. The presence of pufLM genes was also revealed in a new isolate of Methylocapsa palsarum, strain NSB8, which was obtained in this study from a tundra wetland of European Northern Russia. The presence of phototrophy-related genes in all available strains of the abovementioned species indicates their functional importance for these bacteria and suggests realization of the phototrophic potential under certain environmental conditions.