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Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (delta13C) and hydrogen sulfide and sulfate (delta34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated.

A short survey and critical analysis of previously proposed criteria for growth control of populations of microorganisms in the chemostat are presented. Based on the analysis of a mathematical model of the steady-state of a microbial population in the chemostat, an adequate control criterion is suggested, along with a method to identify the corresponding regulating factors. The new control criterion is expressed as a product of the factor transformation coefficient and the biomass sensitivity coefficient (SC) with respect to the change of the factor at the chemostat inlet (referred to in the sequel as the biomass SC). The control criterion determines the strength of the control exerted by this or that factor. The method of determination of the regulating factors consists in experimental determination of the real SCs for factors and the biomass and in calculating on this basis the corresponding ideal SCs for constant factor transformation coefficients. The ideal SCs are shown to add up to an integer value, a constraint that we call "quantization" relationships. Such relationships are used to test the completeness of the drawn list of control factors. The proposed method was applied to our own and literature data.

The feedback level (FBL) in growth regulation has been determined in the experiments on Escherichia coli O-124 on the basis of the theory developed by Degermendzhy et al (1989). FBL is here determined as a function of variations in growth acceleration caused by discrete decrease in bacterium concentration, the medium chemical composition being preserved. It estimates by integration regular action of all chemical density factors. FBL has been determined on periodic cultivation with glucose. In various phases of growth the native culture was diluted with a filtrate of its own. As the sample had grown up, variations in growth acceleration were calculated against the reference specimens. The value of FBL was definitely anything but zero at the end of the experimental phase and in the phase of growth deceleration, and it was equal to -20 divided by -200 (h.g/l). The feedback component was also calculated from the obtained dependence of the growth rate on the glucose concentration. It amounted to mumax = 0.55 +/- 0.05 h-1, Ks = 2.5 +/- 0.7 mg/l. Regulation relative to glucose was 0.5-40% of FBL. This indicates that there are other regulators of growth. Being sufficiently accurate, the new method may supplement microbiological means of determining the growth regulating cell-density factors.