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Biomedical subjects

G A Medvedeva

Publications and source records attributed to G A Medvedeva.

At least 19 recordsLinked to original sources
PubMedDate not supplied

[Cytological mechanisms involved in assimilation of n-alkanes by yeasts].

The paper describes cytological mechanism of adaptation of yeasts to assimilation of aliphatic hydrocarbons added to a growth medium as a sole source of carbon. The process was studied by light optical and electron microscopy, employing fluorescent labelling and electron microscopy contrasting. Two types of yeasts were found, which differed by the response of the cell walls to hydrocarbons: those that formed "channels" and those that did not form them. Cytological response to hydrocarbon assimilation was detected also in the mitochondria and canals of the endoplasmic reticulum. Components of the Golgi apparatus may also participate in this process, in particular, in formation of peroxisomes (microbodies). Close contacts of the yeast cells with the hydrocarbon being assimilated is important; assimilation may start in a close vicinity of the cell walls. The rate of flavin production by Candida tropicalis 303 IBFM increases during growth on solid paraffins, beginning with C20-paraffin.

Adaptation, Physiological↗
PubMedDate not supplied

[Increased flavinogenesis in 1 of the strains of Candida tropicalis].

Candida tropicalis IBFM 303 is capable of the active production and liberation of flavins during the oxidation of solid paraffins with the carbon chain consisting of 20 carbon atoms and more. Unlike other known strains, this strain does not accumulate considerable amounts of the vitamin neither on media containing liquid n-paraffins not on media with glucose, even under the conditions of iron deficiency.

Alkanes↗
PubMedDate not supplied

[Yeast peroxisomes, their development and operation].

Yeast peroxisomes (microbodies) were studied, particularly with yeast methylotrophs, using light-optical microscopy, viz. intravitam phase- and anoptral-contrast microscopy, with cytochemical as well as fixed and stained objects. The data obtained were compared with cytochemical as well as fixed and stained objects. The data obtained were compared with other evidence that we had gained on methylotrophs studied by electron microscopy and with the results obtained by investigating the peroxisomes of yeast cultures grown on nutrient containing other carbon sources. The activity of exocatalase and endocatalase, the enzymes characteristic of peroxisomes, was assayed at different growth phases of yeast methylotrophs and was found to be correlated with the cycle of development of peroxisomes. The content of biotin and inositol and its dynamics were studied in the methylotroph cells. Possible origin of peroxisomes is discussed as well as their development and the mechanism of degradation. A close contact and functional relationship have been established between peroxisomes and mitochondria.

Biotin↗
PubMedDate not supplied

[Effect of elevated temperature on the morphology of a chemostat culture of Candida utilis yeasts and on their content of nucleic acids].

The effect of elevated temperature (40 degrees C) on a chemostat culture of Candida utilis was studied at different rates of dilution, D = 0.1 and 0.3 hr-1. The cells in the fermenter being in the stationary state at the optimum temperature of 30 degrees C were gradually washed-out 5 hours after the action of this temperature, and the population consisted of non-divided cells. In the majority of such "double" cells, the nucleus was contained in both the parent and the daughter parts. The content of RNA decreased by 31%, that of DNA, by 20%, and that of protein, by 13% (per 1 mg of biomass).

Candida↗
PubMedDate not supplied

[Effect of raised temperature on the developmental cycle of Candida utilis yeasts].

The effect of the submaximal temperature (41.5 degrees C) on growth was studied with a synchronous periodic yeast culture. If the cells were subjected to the action of elevated temperature at the beginning of the growth cycle, the formation of buds was not inhibited in contrast to the separation of nuclei between the daughter and parent cells. If the cells started their growth cycle at the optimal temperature of 32 degrees C and, after spending 0.6 of the cycle at this temperature, were subjected to a temperature of 41.5 degrees C, the separation of nuclei between the daughter and parent cells took place, but the cells were not entirely separated one from another.

Candida↗
PubMedDate not supplied

[Formation and degradation of peroxisomes in yeasts].

The formation, development and degradation of peroxisomes were studied directly in growing yeast-methylotrophs under the microscope using anoptral and phase contrast. The degradation of peroxisomes was caused by their degeneration and dislocation to the central vacuole of the yeast cell. A fluorescent-microscopic technique was elaborated for detecting selectively the crystals of catalase in the cells. As was shown by intravitam studies, electron microscopy and cytochemistry, peroxisomes are directly connected with the central vacuole of the cell, enzymes being transferred from the former into the latter. Experiments conducted with different cultures have demonstrated that the high activity of exocatalase is typical of methylotrophic yeast organisms. The highest activity that was exhibited for a long period of time was found in Torulopsis molischiana.

Ascomycota↗
PubMedDate not supplied

[Use of the fluorescence method to detect and quantitatively determine lipids in the cells of microorganisms].

Techniques have been developed for the detection and quantitative determination of lipids in the living cells of microorganisms (after their fixation by heating) using benzimidazole luminophores synthesized by Monocrystalreactive (USSR). When the yeast cells are stained by a luminophore, the latter is selectively bound to cellular lipids producing a brightly fluorescent complex. The intensity of fluorescence increases proportionally to an increase in the concentration of lipids in the microbial mass. The intensity of fluorescence of a microbial suspension is recorded using a spectrofluorimeter at the excitation and fluorescence maxima of 405 and 475 nm respectively. In order to assay the content of lipids in microorganisms which do not produce a homogeneous suspension, the luminophore bound to lipids is extracted from the cells with hot octane. The absolute content of lipids in the biomass is determined using a standard curve which shows the intensity of fluorescence of microorganisms and their octane extracts as a function of the lipid content in the cell.

Ascomycota↗
PubMedDate not supplied

[Structural changes in Candida lipolytica cells during citric acid biosynthesis].

The techniques of light and electron microscopy were used to study structural changes in Candida lipolytica cells related to limitation of their growth and a nitrogen source in medium with glucose and hexadecane and transition of the culture to the production of citric acids. Changes in the content of protein in the cell and in the activities of enzymes of the citrate and glyoxylate cycles located in mitochondria and peroxysomes of the yeast were investigated at the same time. The results characterizing cytological changes in the cell of C. lipolytica in the conditions of citric acid biosynthesis fit in well with the data on protein content and enzyme activities in the cells obtained by biochemical analysis. The transition of the yeast cells to the overproduction of citric acids has been shown to be related to profound rearrangements of the cell: the inhibition of protein synthesis; changes in the structure of the cytoplasm; the appearance of vacuoles of an irregular shape, often in contact with the mitochondria; changes in the mitochondrial and peroxysomal apparatus; the accumulation of lipids. It has been demonstrated once again that the peroxysomal apparatus of the yeast cell has a relationship with the metabolism of n-alkanes.

Candida↗