Diversity of Novel Uncultured Prokaryotes in Microbial Communities of the Yessentukskoye Underground Mineral Water Deposit

Caucasian Mineral Waters is a unique territory, where various types of mineral waters with overall daily flow over 16 000 m3 are concentrated in a relatively small area. The Yessentukskoye deposit is characterized by high diversity of water types, of which Yessentuki nos. 17 and 4 are produced in the greatest amounts. Biogeochemical activity of microorganisms inhabiting the subsurface hydrosphere is one of the proposed mechanisms responsible for the genesis of these waters. The influence of microbial communities on the quality of balneological water resources is presently quite poorly studied. This is the first report on characterization of two communities inhabiting the water-bearing rocks and mineral waters of the Yessentukskoye deposit. The 16S rRNA gene profiling of these communities revealed predominance of uncultured archaea of the phylum Hadarchaeota (36.6%) in the Yessentuki no. 17 water retrieved from the well 46 and of several new classes of uncultured actinobacteria (29.4%) in the Yessentuki no. 4 water retrieved from the well 49-E. Significant differences were revealed in the structure of microbial communities inhabiting the water-bearing horizons of these two wells having different hydrochemical characteristics. Enrichment and pure cultures of the microorganisms belonging to the less abundant taxa were obtained. Analysis of metadata on genomic properties of prokaryotes of the dominant taxa, revealed in this work, indicates their ability to grow chemoautotrophically and thus, their potential involvement in redox transformations of the water-bearing rocks and the gas component of mineral waters.

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