## 2 Materials and Methods
### Procedures  
For DNA isolation from clays, the sample (2 g) was dispersed in 10 mL of Tris-EDTA buffer. DNA was isolated using the specialized DNeasy PowerSoil HTP 96 Kit (384) (Qiagen, Venlo, The Netherlands) the specialized kit for DNA isolation from soils, according to the manufacturer's recommendations. In preparing libraries for amplification, variable parts of a gene of the V3-V4 region of 168 rRNA were selected: for amplification of the V3-V4 region, the degenerate primers For341 (5\({}^{\prime}\)-CCTACGGGNBGCASCAG-3\({}^{\prime\prime}\)) and Rev806 (5\({}^{\prime\prime}\)-GGACTACHVGGGTWTCTAAT-3\({}^{\prime\prime}\)) were used. For amplification of the V4 region, the degenerate primers For515 (5\({}^{\prime\prime}\)-GTGBCAGCMGCCGGTAA-3\({}^{\prime\prime}\)) and Rev806 (5\({}^{\prime\prime}\)-GGACTACHVGGGTWTCTAAT-3\({}^{\prime\prime}\)) were used. Amplification was performed by real-time PCR on a CFX96 Touch (Bio-Rad, Hercules, CA, USA) device using qPCRmix-HS SYBR (Eurogen, Moscow, Russia). Denaturation, primer annealing, and chain elongation for the V3-V4 region were carried out at temperatures of 96, 54, and 72 \({}^{\circ}\)C, respectively, and steps for the V4 region were carried out at temperatures of 96, 58, and 72 \({}^{\circ}\)C, respectively. Purification of the desired product from each batch was conducted with Agencourt AMPure XP (Beckman Coulter, Brea, CA, USA) magnetic particles. Furthermore, high-throughput sequencing was performed via the MiSeq system (Illumina, San Diego, CA, USA) using a reagent kit (MiSeq Kit v2, 500 cycles, Illumina, USA). \begin{table}
\begin{tabular}{c c c} \hline
**Clay Type** & **Designation** & **Sample** \\ \hline Bentonite & B-1 & Kutch deposit (India) [33] \\  & B-2 & Tagansk deposit, Dinozavrov (Kazakhstan) [34] \\  & B-3 & Ceraceous bentonite, Kamalinsk deposit (K Krasnoyarsk region, Russia) [10] \\  & B-4 & 10 th Khutor deposit (Kakassiya, Russia) \\  & B-5 & Zyryanskoye deposit of bentonite (Kurgan oblast, Russia) [10] \\ Kaolin & K-1 & Kantatsk deposit (Krasnoyarsk region, Russia) [10] \\  & K-2 & Kampanovsk deposit (Krasnoyarsk region, Russia) [11] \\ \hline \end{tabular}
\end{table} 
Table 1: Description of the clay materials. Respiratory activity was determined using the MTT test [39] under oxic and anoxic conditions. Before spectrophotometry of the oxidized formazan complex, the samples were centrifuged at 7000 g to remove the clay suspension. The coefficients of the respiratory activity increase were calculated as the ratio of activity on day 15 to the initial value for oxic (KMT Tox) and anoxic conditions (KMT Tanox). Concentrations of elements in the solution were determined by mass spectrometry with inductively bound plasma on Element-2 (Thermo Scientific, Waltham, MA, USA). The samples were filtered through a 0.22 nm filter, acidified with nitric acid to pH 1. Biological leaching was calculated as the ratio of ion concentrations in the experiment to the value for the control (sample treated by UV and without organic substance). Concentrations of elements were measured by ICP-MS.  
Sulfide concentration was determined calorimetrically with dimethyl-p-phenylenediamine according to the modified method of [40]. The mineral composition of the clay samples was determined on a -Xray diffractometer \"X'pert PRO MPD\" manufactured by PANalytical (Almelo, The Netherlands) with Cu K\(\alpha\) anode at 50 kV and 40 mA in continuous mode of recording X-ray patterns, (step 0.02 deg 20, pulse acquisition time 1 s) at the mineralogical department of the FSBI VIMS. Detection limits depend on crystallinity but were typically 0.1-1 wt%. In general, the crystallinity of the measured samples was quite high. Interpretation of results was carried out using internal standards according to the methodology of the FSBI VIMS. Concentrations of the major and extrinsic elements in the samples were determined by X-ray spectral fluorescence analysis on Axios mAX Advanced sequential vacuum spectrometer (with dispersion by the wavelength) (PANalytical, Almelo, The Netherlands).