Microbiological Monitoring of Lake Baikal

The microbial community is not only a natural component of the ecosystem of rivers, reservoirs, and lakes, but also one of the main indicators of their ecological situation. For the public water supply, water reservoirs are often used which are affected by regular or accidental contamination, which greatly influences the water quality. Microbial indicators, limiting values of which are set by the relevant regulatory documents, are defined both for the water supply and for drinking water resources. We provide an overview of the main regulatory documents used in the Russian Federation to assess the microbiological quality of water resources and of methods and results about monitoring of Lake Baikal. Lake Baikal is a well-known example of an oligotrophic deep-water lake which serves as a source of drinking water. The microbial communities of Lake Baikal are formed in the unique extreme environmental conditions determining their metabolism: a low nutrient content and low average annual temperature in the water column. The microbiological indicators for the pelagic zone of the lake are quite constant, as was shown by long-term observations. However, in these ecological conditions the possibility must be taken into account that the water contains microorganisms potentially hazardous to human health. Systematic annual results have been presented (since 2005) of the microbiological monitoring of coliform bacteria, thermotolerant coliforms (TTC), coliphages, as well as Pseudomonas, Clostridium and Enterococcus in Lake Baikal. It is shown that the spatial distribution of allochthonous organotrophic and opportunistic bacteria is associated with the local anthropogenic impact: settlements, deltas of the main tributaries or domestic wastewater discharge. In the deep layers of the pelagic zone of the lake, no groups of opportunistic bacteria were found. Moreover, as the water depth increased, changes were found in the structure of the microbial community. Oligotrophic and psychrotrophic microorganisms were predominant there, while the amount of organotrophic microorganisms did not exceed the background level. The widespread prevalence of uncultivable bacterial forms in the natural environment and the ability of pathogenic and opportunistic bacteria to move into an uncultivable state make them of sanitary significance. It has been demonstrated that new species of heterotrophic microorganisms can be cultivated when the culture media and cultivation conditions are adapted. The experiments show the possible mechanisms of survival for opportunistic bacteria. During the cultivation of Enterococcus faecalis in the Baikal water at a low temperature, cells moved into a viable, but uncultivable state and restored their ability to reproduce after the addition of the nutrient.