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Microbial communities of terrestrial mud volcanoes are involved in aerobic and anaerobic methane oxidation, but the biological mechanisms of these processes are still understudied. We have investigated the taxonomic composition, rates of methane oxidation, and metabolic potential of microbial communities in five mud volcanoes of the Taman Peninsula, Russia. Methane oxidation rates measured by the radiotracer technique varied from 2.0 to 460 nmol CH4 cm−3 day−1 in different mud samples. This is the first measurement of high activity of microbial methane oxidation in terrestrial mud volcanos. 16S rRNA gene amplicon sequencing has shown that Bacteria accounted for 65–99% of prokaryotic diversity in all samples. The most abundant phyla were Pseudomonadota, Desulfobacterota, and Halobacterota. A total of 32 prokaryotic genera, which include methanotrophs, sulfur or iron reducers, and facultative anaerobes with broad metabolic capabilities, were detected in relative abundance >5%. The most highly represented genus of aerobic methanotrophs was Methyloprofundus reaching 36%. The most numerous group of anaerobic methanotrophs was ANME-2a-b (Ca. Methanocomedenaceae), identified in 60% of the samples and attaining relative abundance of 54%. The analysis of the metagenome-assembled genomes of a community with high methane oxidation rate indicates the importance of CO2 fixation, Fe(III) and nitrate reduction, and sulfide oxidation. This study expands current knowledge on the occurrence, distribution, and activity of microorganisms associated with methane cycle in terrestrial mud volcanoes. [ABSTRACT FROM AUTHOR]

The processes of microbially induced precipitation of calcium carbonates are widespread in natural environments and are an important part of the biogeochemical carbon cycle. These processes comprised the basis of new "biocementation" technologies, which are extensively developing worldwide during the last decade. These technologies are aimed at designing the novel "self-healing" construction materials, as well as at maintaining the strength of various buildings and structures. Since the optimal conditions for calcite formation are high salinity and alkalinity, the search for calcifying microorganisms in a variety of ecosystems, including extreme ones, is of interest. At present, many strains of halophilic and halotolerant bacteria, that induce calcination, have already been isolated and tested in pilot industrial processes. Most of these bacteria possess urease activity, which is the main contributor to the binding of calcium ions to insoluble carbonate. A wide variety of natural ecosystems with optimal conditions for the development of calcifying urobacteria, as well as the economic demand for biocementation technologies, stimulate interest in the search for more and more novel strains of these microorganisms. One of the promising resources to be screened for such organisms is the ecosystem of the drying Aral Sea and the adjacent desert and semi-desert Aral region. Here we present the results of screening various extreme ecosystems of the Aral region for the presence of calcifying microorganisms. We obtained 28 pure cultures of heterotrophic aerobic bacteria from samples of plant residues and soils of the Aral Sea region, 4 of which had urease and calcifying activities. Their activities were compared with those of the strains presently used to produce biocementing mixtures. We have identified the phylotypes of putative calcifying microorganisms in microbial communities of desert soil, thermal waters, and bottom sediments of a salt lake, and described the phylogenetic diversity of these communities. Our results indicated the wide distribution of calcifying microorganisms in the ecosystems of the South Aral region and highlighted the expediency of screening them for the new biotechnologically relevant strains of these organisms. [ABSTRACT FROM AUTHOR]

A method for rapid detection and identification of hyperhtermophilic archaea of the family Thermococcaceae based on PCR amplification of 16 rRNA gene fragments with two primers was developed and used for identification of new isolates.