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Biomedical subjects

I L Rabotnova

Publications and source records attributed to I L Rabotnova.

69 records · Page 4Linked to original sources
PubMedDate not supplied

[Effect of the protein synthesis inhibitor chloramphenicol on the basic growth indices of continuous and periodic Bacillus megaterium cultures].

The action of chloramphenicol, a specific inhibitor of bacterial growth and an inhibitor of protein synthesis, was studied in the conditions of continuous and batch cultivation. Steady states of the population within the range of D from 0.2 to 0.7 hr-1 were obtained at a concentration of the antibiotic equal to 20 microgram per liter. The shape of the chemostat curve in the presence of chloramphenicol in the medium indicates that the antibiotic slightly decreases mu max and considerably diminished Y. A change of limiting factors occurs along the chemostat curve at different dilution rates (0.2, 0.4 and 0.7 hr-1): one-, two- and three-factor effects on the population were observed. Steady states of the population in the chemostat are possible by chloramphenicol concentrations of 10 to 100 microgram per litre; in this case, cellular metabolism changes in the following nonspecific way: less effective energy processes are activated, the Y decreases as well as protein content in the cells, but the content of poly-beta-hydroxybutyric acid in the biomass increases. If chloramphenicol is taken at a concentration of 1000 microgram per litre (a dose strongly inhibiting the growth rate), other changes specific for this inhibitor are found: the content of protein decreases while that of RNA increases, and substances of nucleotide nature are released into the medium. The changes remain for many generations. The data show that it is possible to change the ratio between cell polymers in growing population.

Bacillus megaterium↗
PubMedDate not supplied

[Transitional states in a chemostat culture of Candida utilis].

Transient states of the chemostat Candida utilis 1668-3-37 culture were studied when its growth was limited by ethanol and an abrupt acidification of the medium from pH 5.0 to 2.2 was done or when the dilution rate was rapidly changed from D = 0.1 to 0.3 h-1 and back to 0.07 h-1. The pH shock was found to cause stronger oscillations in a number of parameters (the weight of dry biomass, the content of residual ethanol, the content of RNA in the cells) than a change in the dilution rate. In the latter case the population density changed more smoothly than the content of RNA did. DNA content remained at one and the same level in all of the experiments. All of the oscillations were observed only in the first generation after a shock; there upon, the culture remained for a long time (7 to 10 generations) in a very stable state typical of chemostat cultures. The oscillations induced by the unfavourable pH of the medium were compared with those caused by an abrupt change in the dilution rate. The pH shock brought about multiple damping oscillations of the parameters whereas a change in the dilution rate resulted, most often, in a merely one oscillation.

Candida↗
PubMedDate not supplied

[Method of calculating the specific growth rate of microorganisms by measurements of the substrate or product concentration].

A procedure and formulae are proposed for calculating the specific rate of microbial growth; these are based on measuring the concentration of either a limiting substrate or a product involved in the growth of a microorganism. Only the concentrations of a substrate (S) or a product (P) are determined periodically in the course of the cultural growth whereas the biomass yield (chi) in the medium is established only after long time intervals. The proposed equations may be used for controlling the specific growth rate in large-scale processes by the concentration of a product (or a substrate) using a computer, as well as in laboratory studies of mu as a function of the conditions for growth of slowly growing microorganisms.

Bacteria↗
PubMedDate not supplied

[Effect of zinc ions on Candida utilis].

The effect of zinc on the growth of Candida utilis was studied as well as on the rates of RNA and protein synthesis, and the uptake of zinc ions by the cells. The kinetics of C. utilis growth inhibition by zinc ions can be described by the equation for noncompetitive inhibition of enzymatic reactions. The uptake of zinc is a two-phase process. Zinc ions are adsorbed by the surface of the cell at the first phase, and are actively transported inside the cell at the second phase. Protein synthesis is suppressed by zinc ions more than RNA synthesis. Apparently protein synthesis is most sensitive to zinc among other metabolic processes and its inhibition caused deceleration of growth and then death of cells.

Candida↗
PubMedDate not supplied

[Nonspecific stress in Candida utilis under growth inhibition by a specific inhibitor].

The physiological state of Candida utilis chemostat cultures was studied when the growth was limited with glycerol at D from 0.047 to 0.35 hr-1, and compared with the same cultures inhibited with cycloheximide. This compound at a concentration of 1 mg/litre almost did not inhibit the growth, but the value of the growth yield decreased from 0.45 to 0.38; the content of protein fell, on the average, from 44 to 35% of the dry biomass weight; the content of polysaccharides increased from 22 to 30%; the content of nucleic acids and lipids did not change; the liberation of keto and amino acids into the medium slightly increased. The population became heterogeneous, the cells increased in size, the separation of daughter cells from the parent ones became complicated, and the number of vacuoles in the cells increased. All of these changes, apart from a significant decrease in the content of protein, are also typical of the action of various nonspecific growth inhibitors.

Candida↗
PubMedDate not supplied

[Effect of Zn2+ on growth and the properties of Candida utilis in continuous cultivation].

The purpose of this work was to study the effect of zinc ions on the growth and physiological properties of the chemostat culture of Candida utilis BKM Y-1668. Zinc at a concentration of 250-300 mg/l was found to inhibit the growth of the culture. The resistance of the culture to zinc ions can be increased within 40 generations if the yeast is grown in the regime of chemostat and the concentration of zinc ions is gradually increased. The growth of the resistant culture by zinc ions was inhibited at a concentration of 500 mg/l. If the yeast was cultivated with an addition of the inhibitor, the economic coefficient decreased, while the utilization of glycerol, nitrogen and phosphorus per 1 g of the biomass increased twofold and more; the rate of oxygen uptake by the cells and the rate of carbon dioxide evolution decreased, whereas the concentration of keto and amino acids in the medium increased.

Candida↗
PubMedDate not supplied

[Periodic changes in the morphophysiological properties of chemostat culture of Candida utilis yeasts under alternating temperatures].

The object of this work was to find out whether it was possible to cultivate yeasts in chemostat in varying regime: at multiple changes to temperature from the optimal one (31 degrees C) to the supraoptimal one (37 degrees C) and back with a frequency comparable to the generation time; this regime was alternated during 32 generations. The cultures were compared with chemostat cultures grown in steady-state regimes at 31 or 37 degrees C. The value of Y, the composition of cells and morphometric characteristics were determined by the optical-structural computer analysis. The size and shape of cells and the optical properties of the protoplasm were found to be in the oscillatory regime correlating with changes in the growth temperature and periodically tending to the normal characteristics. The value of Y, the content of RNA and protein in the biomass gradually stabilized. A possibility, in principal, to continuously cultivate yeasts is discussed when the conditions of the environment are rhythmically changed and the process is controlled in the morpho-physiological characteristics of the cells.

Candida↗
PubMedDate not supplied

[Binding of silver ions by Candida utilis cells].

Binding of silver ions by the cells of Candida utilis involves their adsorption on the cell surface. It was found that 90% of all silver bound by the cells was localized in the fraction of cell walls and cytoplasmic membranes. The sensitivity of protoplasts to the toxic action of silver ions is much higher than that of intact cells. The toxic effect of silver ions is supposed to be related to changes in the functions of cytoplasmic membranes.

Binding Sites↗
PubMedDate not supplied

[A mathematical model of inhibition of the growth of Candida utilis by heavy metal ions].

A mathematical model described in this paper, contrary to other models, takes into account transport effects during penetration of the inhibitor into the cell of a micro-organism, and also a possibility of partial inactivation of the inhibitor during formation of complexes. It changes into models of Monod and Monod--Jerusalimsky at extreme values of parameters. Theoretical steady-state concentrations of the biomass in chemostat predicted on the basis of this model coincided with values obtained in experiments with limitation of growth of Candida utilis by silver ions and copper ions.

Candida↗