[Response of microbial communities of Lake Baikal to extreme temperatures].

The survival rate, metabolic activity, and ability for growth of microbial communities of Lake Baikal after exposure to extremely low temperatures (freeze-thawing) for different lengths of time have been first studied. It has been shown that short-term freezing (1-3 days) inhibits the growth and activity of microbial communities. The quantity of microorganisms increased after 7- and 15-day freezing. In the periods of maximums, the total number of microorganisms in the test samples was twice as high as in the control. It was established that after more prolonged freezing the microorganisms required more time after thawing to adapt to new conditions. In the variants with 7- and 15-day freezing, the activities of defrosted microbial communities were three or more times higher than in the control. The survival rate and activity of Baikal microorganisms after freeze-thawing confirms the fact that the Baikal microbial communities are highly resistant to this type of stress impact.

[Indications of pathogenic viruses in water of Lake Baikal and its tributaries]. / Indikatsiia patogennykh virusov v vode ozera Baikal i ego pritokakh.

The waters of 25 large rivers falling into the Baikal Lake, their mouth water areas and open Baikal Lake areas to a depth of 500 m were for the first time in the practice of researches on the Baikal Lake were investigated for markers of hepatitis A virus and rotaviruses. The investigations showed an insignificant contamination of surface waters with pathogenic viruses. The antigens of all studied viruses and high values of bacteria from the Escherichia coli group were recorded in the areas exposed to chronic man-made pollution. Data on the seasonal changes in the distribution of enteroviruses indicated their absence in the annual cycle in the pelagic area of the lake, which suggests that viral particle would not accumulate under the conditions of the Baikal Lake over a long period.

[The classification and the monitoring of the state of mouth riverine and lacustrine ecosystems in lake Baikal based on the composition of local microbiocenoses and their activity]. / Struktura mikrobiotsenozov i ikh aktivnost' kak osnova klassifikatsii i monitoringa sostoianiia rechnykh i priust'evykh lokal'nykh ékosistem Baikala.

The paper presents the results of the long-term investigation of microbial communities in the technogenically vulnerable mouth riverine and lacustrine ecosystems of Lake Baikal. The structural and functional parameters of the microbial communities were analyzed from the standpoint of developing destructive processes. The analysis showed that the total number of microorganisms (TNM), the number of saprophytic bacteria (NSB), and bacterial production (BP) were greater in the river-mouth water than in the near-mouth lake water. In the offshore direction, TNM and NSB decreased by a factor of 1.5 to 2, and BP decreased by a factor of 4 to 7. Based on TNM, NSB, and BP data, we classified the Lake Baikal rivers with respect to the degree of the impact of human activities on them. The degrading capability of the riverine microbial communities was found to be such that they degrade daily from tenths of a percent to 3.5% of the total amount of organic compounds polluted the river waters.