In this work, geochemical and microbiological studies were performed at kudurs in the southeastern part of the Sikhote-Alin mountain range and in the Sikhote-Alin Nature Reserve located in Primorsky Krai, Russia. It was found that the earth material eaten by wild animals in both sites is represented by clay-zeolite tuffs of dacite-rhyolite composition. In the earth material, Na is predominant in bioavailable macronutrients and Zn, light lanthanides, and Y in trace elements. Microbiological studies of geophagic earths revealed a wide range of heterotrophic and autotrophic aerobes and anaerobes involved in the conversion of carbon, nitrogen, and sulfur. Iron- and manganese-oxidizing bacteria and silicate bacteria were identified as well. The isolated pure cultures of heterotrophic bacteria were represented mainly by Gram-positive spore-forming large rods of Bacillus sp. and Gram-negative heterotrophic aerobic and facultative anaerobic microorganisms Burkholderia sp. and Microvirgula aerodenitrificans, which oxidize iron and reduce sulfate. The ability of the bacteria M. aerodenitrificans to reduce sulfates is shown for the first time. According to the literature, the isolated microorganisms are able to actively extract rare earth elements from earth materials, transforming them from the bioinert state to a state accessible to herbivorous mammals.

A small number of ecological-trophic groups of bacteria are noted in saline groundwater’s (30-50 g/L). The obtained data show, that thionic and halophilic forms of saprophytic bacteria dominated, developing in presence of 10% NaCl. Among saprophytic microorganisms, rod-shaped forms of the genus Microbacterium sp. significantly dominated. A significant accumulation of Cu, Co and light REEs by brine microbial communities is shown.

Chemical composition, distribution, structure, and numbers of different physiological groups of bacteria as well as their biodiversity have been researched. It has been shown that thermal waters are alkaline with low-TDS, Na-HCO3 type, and enriched in boron, lithium, arsenic, and strontium. The content of organic carbon in groundwaters from studied wells is low. They show uneven distribution, low diversity, and numbers of physiological groups of bacteria. The most insufficient numbers and the least diverse composition of physiological bacterial groups were registered in the groundwaters of higher temperatures. The study discovered the prevalence of chemolithotrophic thionic bacteria in the community structure, thus indicating the prevailing bacteria-induced oxidation of reduced sulfur compounds in the groundwaters. Silicate, iron- and manganese-reducing microorganisms also prevailed in groundwaters of wells No.3-87 and No.3-51. Low biodiversity of microorganisms with a significant prevalence of Bacillus sp. (50-60%) spore-forming bacteria in the taxonomic structure has been revealed. Thermophilic bacilli mostly included the species of B. flexus, B. licheniformis, B.subtilis, B. cereus, and B. cohnii.

The research was focused on the distribution, composition, structure, numbers and diversity of predominant bacteria of different ecologo-trophic groups in the thermal groundwaters of the Kuldur deposit (Amur Oblast, the Russian Far East). The research results showed uneven distribution of bacteria of different physiological groups in the groundwaters as well as their low numbers. Thionic and iron-oxidizing bacteria predominated in all studied drill holes. Ammonium and nitrite-oxidizing bacteria were also numerous while Bacillus sp., Paenibacillus sp., Brevibacillus sp. were prevalent in the separated pure cultures

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