Abstract
Simple SummaryThe Republic of North Ossetia-Alania, located in the southern part of the North Caucasus, possess a number of hydrothermal habitats, including both subterranean thermal reservoirs and terrestrial hot springs. At the same time, reports on microbiology of numerous geothermal sites are rather scarce for the whole North Caucasus region. In this paper, we report on the first culture-independent metabarcoding study of thermal habitats in the North Caucasus, coupled with a chemical analysis of the elemental composition of water. The results of this work include the conclusions regarding key metabolic characteristics of these habitats as well as detection of few but abundant deep lineages of uncultivated microorganisms which could be regarded as endemic. This study may represent a first step in closing the knowledge gap in extremophilic microbial communities of the North Caucasus.The Greater Caucasus is a part of seismically active Alpine–Himalayan orogenic belt and has been a center of significant volcanic activity during the Quaternary period. That led to the formation of the number of hydrothermal habitats, including subterranean thermal aquifers and surface hot springs. However, there are only a limited number of scientific works reporting on the microbial communities of these habitats. Moreover, all these reports concern only studies of specific microbial taxa, carried out using classical cultivation approaches. In this work, we present first culture-independent study of hydrotherms in the Republic of North Ossetia-Alania, located in the southern part of the North Caucasus. Using 16S metabarcoding, we analyzed the composition of the microbial communities of two subterranean thermal aquifers and terrestrial hot springs of the Karmadon valley. Analysis of correlations between the chemical composition of water and the representation of key taxa allowed us to identify the key factors determining the formation of microbial communities. In addition, we were able to identify a significant number of highly abundant deep phylogenetic lineages. Our study represents a first glance on the thermophilic microbial communities of the North Caucasus and may serve as a basis for further microbiological studies of the extreme habitats of this region.
Highlights
Geothermal areas are unique habitats in which extremophilic microbial realms actively function, carrying out diverse metabolic processes
Despite the fact that active thermophilic microorganisms were found hundreds and thousands of kilometers away from hydrothermal sites [7,8], indicating that at least some of them can bear the cold and oxygenated environments for a long time, it seems that the majority of thermophilic cells have a considerably lower probability to survive under conditions of dehydration or at low temperatures [9]
While microbial communities, which inhabit distantly located but hydrochemically similar hot springs are usually similar on the level of higher taxa, some springs might be inhabited by populations, which include a significant proportion of endemic microorganisms [10]
Summary
Geothermal areas are unique habitats in which extremophilic microbial realms actively function, carrying out diverse metabolic processes. The commonly accepted hypothesis “everything is everywhere” may not be entirely true for microorganisms living in isolated habitats like caves, high altitude areas, or underground reservoirs, as opposed to environments mixed actively by air or water currents [6]. In this context, extremophilic microorganisms, which are extremely resistant to stress, but grow only in harsh environmental conditions, are of particular interest. While microbial communities, which inhabit distantly located but hydrochemically similar hot springs are usually similar on the level of higher taxa, some springs might be inhabited by populations, which include a significant proportion of endemic microorganisms [10]
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