Abstract
Thermal ecosystems associated with underground coal combustion sites are rare and less studied than geothermal features. Here we analysed microbial communities of near-surface ground layer and bituminous substance in an open quarry heated by subsurface coal fire by metagenomic DNA sequencing. Taxonomic classification revealed dominance of only a few groups of Firmicutes. Near-complete genomes of three most abundant species, ‘Candidatus Carbobacillus altaicus’ AL32, Brockia lithotrophica AL31, and Hydrogenibacillus schlegelii AL33, were assembled. According to the genomic data, Ca. Carbobacillus altaicus AL32 is an aerobic heterotroph, while B. lithotrophica AL31 is a chemolithotrophic anaerobe assimilating CO2 via the Calvin cycle. H. schlegelii AL33 is an aerobe capable of both growth on organic compounds and carrying out CO2 fixation via the Calvin cycle. Phylogenetic analysis of the large subunit of RuBisCO of B. lithotrophica AL31 and H. schlegelii AL33 showed that it belongs to the type 1-E. All three Firmicutes species can gain energy from aerobic or anaerobic oxidation of molecular hydrogen, produced as a result of underground coal combustion along with other coal gases. We propose that thermophilic Firmicutes, whose spores can spread from their original geothermal habitats over long distances, are the first colonizers of this recently formed thermal ecosystem.
Highlights
Studies of thermophilic microorganisms that survive and develop at temperatures that are extreme for ordinary life have broadened our understanding of the diversity of microorganisms and their evolution, the mechanisms of adaptation to environmental conditions
We investigated the microbial communities of near-surface coal layer in an open quarry for the mining of brown coal, heated by underground coal combustion
Analysis of the composition of the microbial community of the coal (AL3T) both by 16S rRNA profiling and by metagenomic analysis revealed the presence of only a few dominant groups of microorganisms, almost all of which belonging to the phylum Firmicutes
Summary
Studies of thermophilic microorganisms that survive and develop at temperatures that are extreme for ordinary life have broadened our understanding of the diversity of microorganisms and their evolution, the mechanisms of adaptation to environmental conditions. The phenomena of underground combustion of coal seams are quite widespread in nature and are found in Australia, Germany, the USA (Pennsylvania), China, Russia, India and other countries[1]. The combustion of coal is accompanied by the release of large quantities of gas, which, in addition to CO2, contains hydrogen and carbon monoxide, as well as hydrocarbons[1,3]. Such as hydrogen and CO contained in the coal gases can be used by microorganisms as substrates, which determines the possibility of the development of specific communities of thermophilic microorganisms. We are unaware of any reports of microbiological studies in this area
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