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Modelling of genetically engineered microorganisms introduction in closed artificial microcosms

The possibility of introducing genetically engineered microorganisms (GEM) into simple biotic cycles of laboratory water microcosms was investigated. The survival of the recombinant strain Escherichia coli Z905 (Apr, Lux+) in microcosms depends on the type of model ecosystems. During the absence of algae blooming in the model ecosystem, the part of plasmid-containing cells E. coli decreased fast, and the structure of the plasmid was also modified. In conditions of algae blooming (Ankistrodesmus sp.) an almost total maintenance of plasmid-containing cells was observed in E. coli population. A mathematics model of GEMs behavior in water ecosystems with different level of complexity has been formulated. Mechanisms causing the difference in luminescent exhibition of different species are discussed, and attempts are made to forecast the GEMs behavior in water ecosystems.

Trends in microevolution of microbial populations in open systems.

Microbial populations have obvious advantages as an object of populational analysis, at least in several aspects. First, they exhibit a unique ability for rapid reproduction and, therefore, have very short life spans of generations. Intensive culturing of microorganisms during one or two days may yield as many as 100 sequential generations. Second, microorganisms can be easily grown under specified and controllable experimental conditions in sufficiently simple media, which is very important for good reproducibility of results. The third advantage consists in a large size of microbial populations, which makes it possible to use the well-developed apparatus of the theory of differential equations for mathematical description of processes of population development. All these advantages are actualized in the processes of long-term continuous cultivation of microorganisms, the two major types of which, chemostat and turbidostat, are known since 1950s [1–3]. Chemostat and turbidostat are thermodynamically functioning open system able to function under stable steady states. According to the classification of Eigen, chemostat corresponds to the case of constant fluxes; turbidostat, to the case of constant organization (or constant reaction forces) [4]. If evolutionary changes (e.g., transition from one steady state to another as a result of mutations and selection) occur in such systems, the main characteristics of these evolutionary steps can be determined without loosing the generality of approach (both biological and physical). Today this is not sufficiently realized from the standpoint of methodology, although ample experimental data on transitions in the “evolutionary machineries” of both types have been accumulated [5–7]. At first glance, the kinetics of accumulation of active mutants extruding the original form from the cultivator as a result of autoselection seems to be sufficiently diverse [5, 6]. In the case of turbidostat, these are mutants with an increased maximal specific growth rate and more resistant mutants that can grow more rapidly when growth is inhibited. Forms that are characteristic of chemostat include predominantly mutants with an increased affinity for limiting substrate, more “economic” forms, more viable mutants with a decreased rate of dying, etc. However, despite the apparent diversity of microevolutionary transitions in these two types of open systems, certain common trends can be found during their studying, such as an increase in the flux of energy consumed at different stages of organization of biological objects [7].

A Model of Bacterial Cell Cycle Duration Based on DnaA Dynamics and Estimation of the Population Cost of Bacterial Plasmids

233 The theoretical basis of the study was the hypothesis on the relationship between the durations of the cell cycle and the accumulation of DnaA, the protein initiating chromosome replication. A probabilistic model describing the synthesis of this protein is based on the assumption that the mRNA encoding DnaA and the other mRNAs (including plasmid ones) compete for ribosomes. The time of the accumulation of the initiating amount of DnaA (and, hence, the generation time) has been demonstrated to depend on the number of plasmid mRNAs, which is determined by the number and sizes of plasmid copies, as well as the expression efficiency of their genes. A possible mechanism of an increase in plasmid “cost” at low reproductions rates of bacteria in a chemostat is suggested.