Selection of a Microbial Community in the Course of Formation of Acid Mine Drainage

— Changes in microbial community composition during formation of an acid mine drainage were studied on a model of two water reservoirs located in the Ozernoye open-cast mine for polymetallic ores in Eastern Siberia. The first reservoir, Bu-18, was filled with groundwater, had a neutral pH and low levels of sulfate and dissolved metal ions. The second reservoir, Bu-16, was an acid mine drainage (pH 2.85) filled with the water from Bu-18, which passed through rocks containing sulfide minerals. The Bu-16 water contained 1405 mg/L of sulfate, 164 mg/L of manganese, 78 mg/L of magnesium, and 26 mg/L of iron. Molecular analysis of the microbial communities of two reservoirs, carried out using high-throughput sequencing of the 16S rRNA gene fragments, showed that formation of the acid mine drainage was accompanied by a decrease in microbial diversity and by selection of several dominant taxonomic and functional groups. Chemolithoautotrophic iron- and sulfur-oxidizing bacteria of the genera Leptospirillum, Acidithiobacillus, Gallionella, Sulfuriferula , and Sulfobacillus constituted most of the prokaryotic community in Bu-16. Heterotrophic bacteria of the genera Ferrimicrobium and Metallibacterium , capable of reducing Fe(III) under anaerobic conditions, were present as minor components. Over 20% of the community were members of the Candidate Phyla Radiation group and of the candidate phylum Dependentiae (TM6), known for their parasitic or symbiotic lifestyle. These groups of bacteria were rarely found in acid mine drainage and only in minor quantities. Potential hosts of the Dependentiae , flagellates of the genus Spumella , were found among eukaryotes in Bu-16.