Successional Changes in the Microbial Community of the Alkaline Lake Khilganta during the Dry Season

Microbial processes in a shallow, saline, alkaline Lake Khilganta (Southern Siberia) were studied during the dry season. During the drought, a crust was formed on the lake surface, where low rates of production processes were observed, with predominance of anoxygenic photosynthesis at 2.3 mg C/(dm 3 day). The rates of microbial processes increased after short-term rains. During this period, a thin cyanobacterial mat was formed on the bottom, in which filamentous cyanbacteria Geitlerinema spp. predominated and the rate of oxygenic photosynthesis was up to 18 mg C/(dm 3 day). Subsequent water evaporation and salinity increase resulted in altered community types and their activity. Red spots emerged on the mat surface, where anoxygenic prototrophic members of the genus Ectothiorhodospira predominated. Anoxygenic photosynthesis became the main production process in microbial mats, with the rate of 60 mg C/(dm 3 day). At salinity increase to 200 g/L, the water remained in small depressions on the bottom, where extremophilic green algae Dunaliella sp. predominated, and the rate of oxygenic photosynthesis was 0.877 mg C/(dm 3 day). These changes in the type and activity of microbial communities is an example of succession of microbial communities in Southern Siberia saline lakes during drought.