Thermophilic and mesophilic sulfate reduction by rare biosphere bacteria in acidic metal-bearing mine wastes from the temperate climate zone

Dissimilatory sulfate reduction is the main microbial process that detoxifies metals and increases pH in acid mine drainage. Acidophilic, copper-resistant Desulfosporosinus sp. BG and Desulfosporosinus sp. OT were previously isolated from acidic metalliferous tailings of the Bom-Gorkhon mine in Transbaikalia and Norilsk, respectively. To understand the role of sulfate-reducing bacteria (SRB) in mine tailings, we returned to the Bom-Gorkhon site to measure sulfate-reduction rate (SRR) with radioactive tracer and to estimate the proportion of SRB in the microbial community using 16 SrRNA gene profiling and metagenomic analysis. The SRR measured under ambient temperature conditions was high, reaching 9.86 ± 0.89 µmol SO4 cm- 3 day- 1. Unexpectedly for a temperate biotope, SRR values of the same order of magnitude were recorded at 60 °C. Thermophilic spore-forming Desulfotomaculum and Desulfofundulus are likely involved in the thermophilic process. The spores of thermophilic Desulfofundulus germinating at 20 °C may input into sulfate reduction at in-situ temperature conditions. Metagenomic analysis by dsr gene mapping and 16 S rRNA gene profiling revealed low abundance of Desulfosporosinus and other SRBs, indicating that geochemically important active sulfate reduction in acidic wetland sediments is carried out by a "rare biosphere" consortium. The cultivated BGT and OT strains are described as Desulfosporosinus cupriresistens sp. nov.