Estimating the instability parameters of plasmid-bearing cells. I. Chemostat culture.

What determines the stability of plasmid-bearing cells in natural and laboratory conditions? In order to answer this question in a quantitative manner, we need tools allowing the estimation of parameters governing plasmid loss in different environments. In the present work, we have developed two methods for the estimation of the instability parameters of plasmid-bearing cells growing in chemostat. These instability parameters are: (i) selection coefficient (or cost of the plasmid)alpha and (ii) the probability of plasmid loss at cell division tau(0).

Computer modeling of the biotic cycle formation in a closed ecological system.

The process of biotic turnover in a closed ecological system (CES) with an external energy flow was analyzed by mathematical modeling of the biotic cycle formation. The formation of hierarchical structure in model CESs is governed by energy criteria. Energy flow through the ecosystem increases when a predator is introduced into a "producer-reducer" system at steady state.

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.

[Mathematical modeling of population dynamics of unstable plasmid-containing bacteria during continuous cultivation in a chemostat].

A structural approach to studying the regularities of the population dynamics of unstable recombinant bacterial strains in a chemostat was elaborated. The approach is based on the mathematical modeling of cell distribution in a population with different numbers of plasmid copies. The effect of decreased selective preference of plasmidless variants of the recombinant strain in the chemostat, which is related to a decrease in the number of plasmid copies in cells upon long-term incubation was analyzed.

[Introduction and long-term storage of recombinant luminescent Escherichia coli strain Z905 in laboratory water microecosystems].

We studied preservation of recombinant Escherichia coli strain Z905 (AprLux+) in liquid microecosystems (LME) after the introduction. E. coli cells were shown to remain viable and preserve the ability to express the cloned lux genes for a long time (more than a year) in LME.

[Phenotypic variability of a recombinant luminescent strain of Escherichia coli in water microcosms].

The behavior of Escherichia coli Z905, carrying a recombinant plasmid pPHL7 with genes determining ampicillin resistance and bacterial luminescence, and the efficiency of expression of cloned genes were studied after introduction of the strain into model aqueous ecosystems with different trophic chain lengths. The E. coli Z905 variants isolated from ecosystems after different periods of time were found to vary in their resistance to ampicillin (from 50 to 0.

[Dynamics of the population structure of the Escherichia coli recombinant strain during continuous culture].

The populational structure of the Escherichia coli strain Z905 containing the recombinant plasmid with the phenotype AprLux+ was studied in chemostat. It was shown that the stability of the ratio of plasmid containing cells and cells without plasmids depends in the first place on the presence of the selective factor (ampicillin) in the medium and on the sources of carbon and energy limiting growth.

[Substrate inhibition and Candida tropicalis growth limitation by phenol in continuous chemostat and pH-stat cultures].

The aim of this work was to investigate phenol decomposition by Candida tropicalis 29-10 adapted to phenol as a sole source of carbon and energy, and to elucidate the nature of resistance of continuous cultures decomposing phenol in processes with two types of control, viz. in chemostat and in pH-stat. The results suggest the resistance of the pH-stat regime of microbial cultivation during substrate inhibition.

[Candida mycoderma growth inhibition with phenol and the autoselection of resistent forms under continuous pH-stat cultivation].

The effect of phenol on the growth rate and respiration was studied with the yeast Candida mycoderma cultivated in the pH-static conditions with continuous recording of the principal kinetic parameters of the population. The kinetics of growth inhibition with phenol was studied. Adaptation of the culture in terms of the growth rate and the rate of oxygen uptake was detected within 10--15 hours of cultivation.