[Effect of heavy water on the growth, glucose assimilation and stability of Escherichia coli to freezing-thawing]. / Vliianie tiazheloi vody na rost, assimiliatsiiu gliukozy i ustoichivost' Escherichia coli k zamorazhivaniiu-ottaivaniiu.

Growth and resistance to freezing--thawing of Escherichia coli B-1640 were investigated during cultivation in synthetic media prepared with H2O and D2O. It is found that during cultivation in D2O the maximum specific growth rate decreases and the duration of the exponential growth phase increases. During the growth in D2O the glucose consumption rate drops in the exponential growth phase, the lactate content in the culture liquid is lower by two orders than that in H2O; the resistance to freezing--thawing is lower than that in H2O. After leaving the exponential phase the culture in D2O restores specific growth rate, glucose consumption rate and resistance to freezing--thawing up to the values obtained during the growth in H2O. The translation ability of ribosomes isolated from cells grown in D2O and H2O is the same. We conclude that the culture adapts to D2O during the exponential growth phase. It is suggested that during the adaptation the second carbon source is used which compensates the consequences of the disturbances of glucose metabolism and transport caused by deuteration of the cell content in the adaptation to D2O.

[Physiological properties of Saccharomyces cerevisiae during sine-modulated and stepwise changes in the medium pH]. / Fiziologicheskie svoistva Saccharomyces cerevisiae pri sinusoidal'nykh i stupenchatykh izmeneniiakh pH sredy.

The responses of a chemostat Saccharomyces cerevisiae culture (D = 0.1 h-1) to a stepwise increase or decrease in the pH of the medium were shown to be asymmetric. When the pH was lowered from 6.5 to a value above 0.3, the rates of oxygen uptake and carbon dioxide evolution rose for a sort period of time whereas the optical density of the culture fell down. The detected changes in the properties of the culture were identical with those which had been observed in the course of spontaneous undamped oscillations in the physiological parameters of the continuous C. cerevisiae culture. Apparently, in both cases, the energy status of cells changed when the oxidative type of metabolism was substituted by fermentation. When the pH of the medium was elevated within the same range (4.7-6.5), the response of the culture was three times as low and its properties changed in the opposite direction. When the pH of the medium was changed in a cyclic sinusoidal manner, oscillations in the physiological characteristics of the culture, identical with spontaneous oscillations were induced at certain values of the amplitude and the frequency of pH changes.

[Analysis of distribution of S. cerevisiae cells for protein content using cell cycle models]. / Analiz razpredelenii kletok S. cerevisiae po soderzhaniiu belka pri pomoshchi modelei kletochnogo tsikla.

Histograms of cell distributions according to protein content obtained by means of flow cytofluorometry characterize the physiological state of the population as a whole and permit to calculate the velocity of protein accumulation in the cell in the course of the cell cycle. Dependence of population heterogeneity on culturing conditions is considered. Mathematical analysis of histograms of continuous cultures of S. cerevisiae is carried out at dilution rates 0.4 hours-1 and 0.05 hours-1. Calculations are carried out on condition that the protein content in the cell rises a) exponentially and b) linearly in the course of the cell cycle. At low growth rate (0.05 hours-1) the distribution is bimodal and therefore it is highly informative. The assumption concerning linear accumulation of the protein allows good approximation of the experimental distributions by the theoretical ones.

[Changes in the volutin levels in yeast cells during cell cycle]. / Izmenenie soderzhaniia voliutina v kletkakh drozhzhei v khode kletochnogo tsikla.

Dimeric distribution of the cell number of Saccharomyces cerevisiae is analysed according to the volume and content of volutin in them. Dynamics of the age composition of the population in time when changing the medium limiting growth for the balanced one is considered. The data obtained indicate that volutin may serve as a regulator when the yeast cells pass the starting point in the division cycle, however, this event has no contrary effect on volutin accumulation.

[Relation of fluctuations in the physiological traits of a continuous Saccharomyces cerevisiae culture to the cell division cycle]. / Sviaz' kolebanii fiziologicheskikh priznakov nepreryvnoi kul'tury Saccharomyces cerevisiae s tsiklom deleniia kletki.

Such physiological characteristics of a continuous Saccharomyces cerevisiae culture as the rate of O2 uptake and CO2 evolution, the rate at which the medium was acidified, were found to vary. When the flow rate was increased from 0.05 to 0.1 h-1, the period of variations also rose (from 3 to 33 h) and two maxima were detected in the quantity of budding cells within one 33-h period of the variations. These findings indicate that the variations do not depend on changes in the physiology of the cell in the course of its division cycle.

[Mechanism of growth limitations in a recombinant strain of Escherichia coli]. / O mekhanizme limitirovaniia rosta rekombinantnogo shtamma Escherichia coli.

A recombinant Escherichia coli strain with the cloned gene of restriction endonuclease EcoR-V was studied. The diauxic growth of this strain under batch conditions, the composition of excreted products and the hyperbolic shape of the chemostat growth curve has made it possible to formulate the following hypothesis. At a high flow rate, one of the first reactions in the tricarboxylic acid cycle or a reaction directly preceding the cycle is a limiting step in the metabolism of E. coli cells. The saturation of the limiting reaction with a substrate at a flow rate higher than the critical one may be responsible for the hyperbolic profile of chemostat curves. The above hypothesis was confirmed by experiments conducted under extreme conditions, in which the composition of the growth medium was changed and the temperature was raised so that the cloned protein synthesis was depressed. Under such conditions, the enzyme composition of the cell was fixed and determined by the physiological state of the culture at a time when the temperature was elevated. The hypothesis was also supported by the results obtained in growing the strain with the induced protein synthesis in media to which various compounds were added.

[Characteristics of the stoichiometric regulation of glycolysis in prokaryotic cells. A model]. / Osobennosti stekhiometricheskoi reguliatsii glikoliza prokariotov. Model'noe issledovanie.

A model is developed to investigate the steady state of the glycolytic system of procaryotic cells which have the hexose transport into the cell coupled with phosphoenolpyruvic acid-dependent phosphorylation. Analysis of the model shows that this phosphorylation results: 1) in stoichiometric connection between the rate of hexose consumption and the utilization of ATP and 2) the stoichiometric positive feedback. The latter can be the cause of bistability, oscillations and other nonlinear phenomena.