A culture-independent study of the structure, functions and methane oxidation activity of microbial communities of geothermal springs in Dagestan

Microbial communities inhabiting geothermal springs in the Republic of Dagestan, Russia, have not been studied by culture-independent methods to date. We have investigated the taxonomic composition, metabolic potential and rates of methane oxidation of microbial communities in two geothermal springs with methane emission located in Dagestan. Methane oxidation rates measured by the radiotracer technique varied from 3.7 to 96.5 nmol CH4 cm^(-3) day^(-1). 16S rRNA gene amplicon sequencing indicates that in the Artuzen hot springs (54oC), with a salinity of 2.5%, the primary production of organic matter is performed by photosynthetic cyanobacteria growing in the water flow, while in the freshwater Miatli hot springs (58oC) primary producers are thermophilic cyanobacterium Thermosynechococcus and photosynthetic members of Chloroflexi. Analysis of metabolic capabilities of the metagenome assembled genomes confirmed that microbial community degrades organic matter produced by phototrophic planktonic Oscillatoriales. Anaerobic bacteria belonging to Anaerolineae and Marinisomatota are the key decomposers of complex organic substances, including cellulose. The main terminal electron-accepting process in this sediment is acetoclastic methanogenesis carried out by the genus Methanocrinis. Thus, our study extends the current knowledge of the phylogenetic and metabolic diversity and activity of the prokaryotes inhabiting terrestrial hydrothermal environments.