Structure and Metabolic Potential of Microbial Communities in High-altitude Lake Enriched with Dissolved Organic Carbon.

It is evident that climate change is causing glaciers to melt at an accelerated rate. This has a noticeable impact on the hydrological regime of high-altitude lakes, as well as the activity of microbial communities. However, the impact of climate change on microbial processes, abundance and diversity of microbial communities in high-altitude lakes remains to be elucidated. The objective of the study was to evaluate the structure, activity and metabolic capacity of microbial communities inhabiting the high-altitude Caucasus lake. Analytical and radiotracer methods were used together with 16S rRNA profiling, and metagenome analyses. Elevated concentrations of dissolved organic carbon (DOC) were observed in both the water column of the lake (12.2–19.4 mg/l) and the pore water of the sediments (6.3–15.8 mg/l). The intensity of photosynthesis in water column was very low. The bulk of phototrophs concentrated on the sediment surface where we suggest they produce organic matter due to sufficient light penetration and warming of the overlying water. The elevated DOC concentrations facilitated the activity of diverse heterotrophic microorganisms, resulting in oxygen depletion and activation of anaerobic processes in sediments. In case of an increase in the average annual temperature of the region, it is possible to predict the transformation of the lake into a eutrophic meromictic reservoir with constantly anoxic water layers, where sulfate reduction and methanogenesis would assume a pivotal role.