Microbiota and Hydrochemistry of Thermal Groundwaters of the Kuldur Spa (Far East, Russia)

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.