Alga-based mathematical model of a life support system closed in oxygen and carbon dioxide.

The purpose of the study was to compare quantitative analysis methods used in the early stages of closed-loop system prototyping with modern data analysis approaches. As an example, a mathematical model of the stable coexistence of two microalgae in a mixed flow culture, proposed by Bolsunovsky and Degermendzhi in 1982, is considered. The model is built on the basis of a detailed theoretical description of the interaction between species and substrate (in this case, illumination). The ability to control the species ratio allows you to adjust the assimilation quotient (AQ), that is, the ratio of carbon dioxide absorbed to oxygen released. The problem of controlling the assimilation coefficient of a life support system is still relevant; in modern works, microalgae are considered as promising oxygen generators. At the same time, modern works place emphasis on empirical modeling methods, in particular, on the analysis of big data, and the work does not go beyond the task of managing a monoculture of microalgae. In our work, we pay attention to three results that, in our opinion, successfully complement modern methods. Firstly, the model allows the use of results from experiments with monocultures. Secondly, the model predicts the transformation of data into a form convenient for further analysis, including for calculating AQ. Thirdly, the model allows us to guarantee the stability of the resulting approximation and further refine the solution by small corrections using empirical methods.

The Principle of Competitive Exception in a Two-Species Community with One Metabolic Regulation Factor.

The validity of the competitive exclusion principle (the Gause's principle) at one metabolic regulation factor is demonstrated for a general model of two-species community. The competitive exclusion principle postulates that a long-term coexistence of species is impossible if their number exceeds the number of density-dependent growth-regulating factors. Previously, this principle was proved for the stationary states in a general model of a community with any number of factors. In the dynamic modes, the number of species in a community may exceed the number of regulating factors. However, under the influence of one factor, only one species survives.

[Microbiological and isotopic-geochemical investigations of meromictic lakes in Khakasia in winter].

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.

[Developing the control criterion for continuous culture of microorganisms].

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.

[Prognostic radioecological mathematical model of the Yenisei river]. / Prognoznaia radioékologicheskaia matematicheskaia model' reki Enisei.

A one-dimensional mathematical model of the Yenisei river ecosystem including hydrological, ecosystem and radioecological blocks has been developed. The model was used to evaluate contribution of different processes (transfer by water masses, dilution, radioactive decay, bioaccumulation) into self-purification of the river water from a radiation pollution and calculate pollution density of ecosystem components (bacteria, phyto-, zooplankton, phyto-, zoobenthos, detritus) with 137Cs and 32P.

[Accumulation of industrial radionuclides by the Yenisei River aquatic plants in the area affected by the activity of the mining and chemical plant]. / Nakoplenie tekhnogennykh radionuklidov vodnymi rasteniiami r. Enisei v zone vliianiia gorno-khimicheskogo kombinata.

The aim of the paper is to investigate accumulation of artificial radionuclides by the Yenisei River aquatic plants collected in the area affected by the activity of the Mining-and-Chemical Combine (Zheleznogorsk) from 1997 to 2000. The samples of aquatic plants were of four species: Potamogeton lucens, Fontinalis antipyretica, Elodea canadensis, and Ceratophyllum demersum. The gamma-spectrometric analysis of the samples of aquatic plants for artificial radionuclides revealed a wide spectrum of long-half-life and short-half-life radionuclides. Radionuclides of activation origin were found in the aquatic plants taken both near the Combine and 200 km down of it. The data obtained suggest that the cooling water of the operating reactor is still being released into the Yenisei. The radiochemical analysis of aquatic plants revealed strontium and plutonium isotopes. Among the aquatic plants, the highest concentration factors for the principal radionuclides were recorded in Fontinalis antipyretica (water moss).

[A new experimental approach to the search for chemical density factors in the regulation of microbial population growth]. / Novyi éksperimental'nyi podkhod k poisku plotnostnykh khimischeskikh faktorov v reguliatsii rosta mikrobnykh populiatsii.

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.

[Comparative analysis of evolution of Eigen's hypercycles and microbial populations in open systems]. / Sravnitel'nyi analiz évoliutsii gipertsiklov Eigena i populiatsii mikroorganizmov v otkrytykh sistemakh.

The models of evolution of Eigen's hypercycles and microbial populations were compared. It has been proved that both above mentioned model descriptions of evolution completely coincide for the case of support constant organization (1). It has been shown that in the case of constant flows (2) for the Eigen's model it is necessary to take into account the dynamics of concentration of energy monomers. The experimental results of microevolution of microbial populations for conditions 1 and 2 are presented.