Biomedical subjects

M V Nefelova

Publications and source records attributed to M V Nefelova.

At least 19 recordsLinked to original sources

PubMed2001

[Morphology of Streptomyces chrysomallus microcolonies in submerged cultivating].

Gel matrix covering microcolonies and individual hyfs and cords of mycelial hyfs was for the first type detected using a special method for making preparations for microscopic examinations. The matrix is observed during culturing streptomycetes in media of different composition for mycelium of different age. Gel matrix renders the colonies a compact shape and can be regarded as a specific structural component of Streptomyces microcolonies. The matrix contains gels differing by hydrophobicity and low-molecular-weight biosynthesis products, including actinomycin antibiotics, which play an important role in maintenance of morphological structure.

Circular Dichroism↗

PubMed2000

[The effect of heat shock on the growth and mycelial morphology of Streptomyces chrysomallus].

The effect of various conditions of heat shock (1 hour at 35, 38, 40, 42, 45 and 50 degrees C) on the growth and morphological features of Streptomyces chrysomallus, an organism producing actinomycin, was studied. A definite regularity in the mycelium morphological changes at high temperatures was observed. After the shock at 35 and 38 degrees C the biomass volume and morphological features of the streptomycete did not markedly differ from those in the control. The shock at 40 degrees C induced the growth inhibition with decreasing the biomass volume by 50 per cent and appearance of submerged spores. When the shock conditions were more rigid (42, 45 and 50 degrees C) the mycelium growth lacked. It is of interest that the temperature of 42 degrees C induced abundant formation of the spores. With further increasing of the temperature to 45 and 50 degrees C the spore formation was not so abundant. The changes in the growth and development of the streptomycete are discussed in relation to the molecular mechanism of the cell protection from temperature shock.

Culture Media↗

PubMed2000

[The effect of heat shock on the formation and composition of actinomycins].

The effect of various conditions of heat shock on production of actinomycins by Streptomyces chrysomallus 2 and their composition was studied. The actinomycin biosynthesis was shown to be the function of the growing mycelium and changed in accordance with changes in the volume of the mycelium and its morphological features after heat shock at various suboptimal temperatures. The temperature shock had a specific action on the antibiotic synthesis: the index of the actinomycin maximum quantity increased after the heat shock at 35 and 38 degrees C and lowered more sharply than that of the biomass volume after the heat shock at the temperatures of 40, 42, 45 and 50 degrees C for 1 hour. After the shock at 38 degrees C the component composition of the actinomycin complex did not significantly change while with addition of exogenic amino acids such as L-valine, L-leucine and L-isoleucine the shock effect on the component composition of the actinomycin complex was marked.

Anti-Bacterial Agents↗

PubMed1999

[Ionophore characteristics of heliomycin].

A highly purified product, identified as a well-known antibiotic geliomycin, has been derived by gradient extraction of the mycelium from Streptomyces robefuscus isolated from soil specimens as a result of purposeful search for a producer of hydrophobic ionophore antibiotics. The ionophore properties of geliomycin are highly labile and inducible. Cationic or anionic nature and the angle of the function performed depend on the concentration, type of electrolyte, protocol of measurements, and some additives used for the preparation of geliomycin electrodes to measurements. Stable development of the cationic function was detected for potassium chloride. The lability of ionophore properties was the highest with ammonium chloride as the electrolyte. Ammonium acetate and potassium and sodium chlorides notably increased the stability of geliomycin electrodes. Selective activity of geliomycin towards potassium ion is a more permanent characteristic. The results permit a conclusion about the inducibility of ionophore properties of geliomycin, which may play an important role in the vital activity of the producer and manifest as a regulatory factor in maintenance of water and acid base balance.

Anti-Bacterial Agents↗

PubMed1998

[Gradient extraction of ammonium specific ionophore antibiotics from mycelium].

Streptomyces brunneofungs 118 and S.griseolus 224 were isolated from natural objects and shown to synthesize ammonium specific products belonging to macrotetrolide compounds. Gradient extraction was applied to the mycelium and it was demonstrated that the compounds were rather labile both in the native cells and on synthetic carriers and could be hydrolyzed by aqueous solutions of acetone and ethanol to various linear oligomers of narctinic acids. Acetone mainly stabilized the monomer and dimer fragments whereas in the ethanol extracts a complete set of the oligomers (from the monomer to the tetramer) was detectable. Graident extract of suspension of the microbial intact cells is useful in the study of some properties and the primary identification of biologically active hydrophobic products even at the early stages of their isolation.

Acetone↗

PubMed1997

[Antibiotic and electrochemical properties of some natural ionophoric compounds from streptomycetes].

The systematic position of 8 Streptomyces strains isolated from nature was determined as a result of purposeful search for producers of ionophore compounds; 7 of them belong to different species. Study of the antibiotic activity of these strains and of antibiotics isolated from them as crystals permit us to hypothesize that Streptomyces may be the test organisms most fit for production of hydrophobic ionophores from streptomycetes. Alteration of the ranges of cationic and anionic selectivity by using different electrolytes indicates a high lability of the natural ionophore compounds, which may be due to their physiological function: to take an active part in the exchange processes of all inorganic ions between the cell and environment. This very property may seriously impede the use of ionophores for some practical purposes, e.g., making ion-selective electrodes.

Anti-Bacterial Agents↗

PubMed1995

[UV-spectroscopic study of complex formation between nonactin and picrates of monovalent cations].

A macrotetrolide preparation including nonactin (about 75 per cent), monactin (about 23 pr cent) and traces of dinactin and trinactin was analyzed with the method of UV spectroscopy. It was shown to form hydrophobic complexes in organic solvents with picrates of univalent cations of ammonium, potassium and sodium. The complex strength depended not only on the cation nature, but also on the solvent and pH of the picrate aqueous solutions. The comparison of methylene chloride used for tetrananactin with chloroform demonstrated that nonactin formed stable complexes in chloroform at neutral pH of the aqueous phase, a solution of picric acid and ammonium chloride.

Anti-Bacterial Agents↗

PubMed1989

[Isolation and properties of macrotetrolide synthase from the mycelium of Actinomycetes].

The formation of cyclic polyester antibiotics (macrotetrolides) from nactinic acids in a cell-free system in the presence of a mycelium homogenate of Streptomyces chryzomallus var. macrotetrolidi, a producer of a complex of homologous macrotetrolide antibiotics, was demonstrated. An enzyme catalyzing the formation of an ester macrotetrolide ring and possessing a specific activity of 360 mumol/min/mg of protein has been isolated for the first time from the mycelium homogenate and purified 176-fold with a 18% yield. Macrotetrolide synthase represents a macromolecular complex with a molecular mass of 360 kDa formed by several heterogeneous polypeptides. The effects of physico-chemical environmental factors on the stability and activity of the enzyme were demonstrated. The optimal conditions for the manifestation of the synthase activity (10 mM Tris-HCl, pH 8.0, 10% ethanol, 2% glycerol, 200 micrograms/ml of nactinic acids) were selected. The kinetic parameters of the enzyme-catalyzed macrotetrolide synthesis reaction (Km = 2.9.10(-4) M, V = 22.3 microM/min) were determined.

Anti-Bacterial Agents↗

PubMed1988

[Enzyme activity of Bacillus polymyxa 153, the producer of polymyxin B, during sporulation and biosynthesis].

Metabolic properties of Bacillus polymyxa 153 were studied during vegetative growth, polymyxin B biosynthesis and active sporulation. In the cell extracts there was detected activity of exoproteases, endoproteases, tricarboxylic acid cycle dehydrogenases and pyruvate dehydrogenase. The enzymes activity in the cells growing into spores was higher than that in the cells of the vegetative developmental type. The activity of the enzymes depended on the culture age.

Bacillus↗

PubMed1987

[Intracellular ATP content and nonactin biosynthesis].

The effect of potassium orthophosphate on growth of the mycelium, its ATP contents and biosynthesis of the macrotetrolide antibiotic nonactin by Str. chrysomallus var. macrotetrolidi was studied. Direct dependence of the ATP contents in the mycelium on the amount of the phosphate added to the medium and consumed by the developing actinomycete was shown. Changes in the intracellular content of ATP depended also on the mycelium age. It was characterized by two peaks. Hemin was detected in the actinomycete mycelium. Its levels were sufficiently high and depended on the mycelium age and cultivation conditions, in particular on the phosphate content in the medium. Higher levels of nonactin biosynthesis were characteristic of the mycelium with lower contents of ATP, proteins and hemin. Intensive production of the antibiotic proceeded at the background of decreasing levels of ATP in the mycelium.

Adenosine Triphosphate↗

PubMed1986

[Effect of orthophosphate on the formation of the antibiotic nonactin].

The potassium orthophosphate added to the media with developing actinomycetes inhibits the nonactin macrotetrolide antibiotic but causes the increase of mycelium growth. The degree of inhibition depends on the quantity of orthophosphate and almost doesn't depend on the time of its adding to the actinomycetes culture. The degree of phosphorus consumption by actinomycetes is higher, the more its content in the media. The antibiotic synthesis takes place during the phosphorus consumption but not after its exhaustion from the media.

Anti-Bacterial Agents↗

PubMed1985

[Nonactin biosynthesis. The incorporation of precursors into the antibiotic molecule].

It was shown that 14C-glucose and 14C-acetate are incorporated with the mycelial suspension of Streptomyces chrysomallus var. macrotetrolidi into the macromolecular compounds of the biomass and into nonactin, an antibiotic of the macrotetrolide group. The dependence of the incorporation on the time of the mycelium incubation with the 14C-substrate was similar for both compounds. Incorporation of 14C-acetate into nonactin was observed at earlier incubation periods, while intensive incorporation of 14C-glucose started after 60-90 minutes of incubation. The culture was shown to have two pathways of glucose metabolism, i. e. glycolysis and pentosophosphate pathway. Under the experimental conditions glycolysis was more important for both the biomass construction and the antibiotic synthesis. Inhibition of various areas of the tricarbonic acid cycle had a significant effect on incorporation of 14C-acetate into nonactin. The character of the effect depended on the site of the inhibitor action: inhibition of aconitase by trifluoroacetate lowered the level of the antibiotic synthesis by 2-4 times and inhibition of succinate dehydrogenase by malonate increased it by 2 times.

Acetates↗

PubMed1985

[Biological action and complex-forming properties of a macrotetrolide antibiotic complex].

Macrotetrolide antibiotic complexes containing 60-80 per cent of nonactin were studied and their high antibacterial activity was shown. The macrotetrolides had a disintegrating effect on the bacterial membrane, which was evident from induction of the protoplast lysis and release of low-molecular compounds from the bacterial cells. The complex-forming properties of nonactin with respect to the ammonium, potassium and sodium ions were investigated in vitro. The selectivity level with respect to the ammonium ions was higher. Nonactin incorporated into an artificial membrane provided a linear dependence of the delta mV on the ammonium chloride concentration within the ranges of 10(-1)-10(-5) M.

Anti-Bacterial Agents↗

PubMed1985

[Macrotetrolide antibiotics from mycelia of Streptomyces chrysomallus].

White crystalline antibiotically active substances identified as macrotetrolides were isolated from the mycelium of four actinomycetous strains, i.e. S. chrysomallus var. I, S. chrysomallus var. III, S. chrysomallus var. carotenoides and S. chrysomallus var. macrotetrolidi. The component composition of the macrotetrolide antibiotics of all four strains was identical. It was characterized by predominance of nonactin, a lower homologue. The composition ratio was the following: 69-79 per cent of nonactin, 19-29 per cent of monactin, 1-3 per cent of dinactin and the traces of trinactin and tetranactin. The strains differed in the intensity of production of the macrotetrolides and the ability to synthesize other biologically active substances.

Anti-Bacterial Agents↗

PubMed1984

[Composition of cell walls of 2 mutant strains of Streptomyces chrysomallus].

The cell walls and peptidoglycans of two mutant strains, Streptomyces chrysomallus var. carotenoides and Streptomyces chrysomallus var. macrotetrolidi, were studied. The strains are organisms producing carotenes and antibiotics of the macrotetrolide group. By the qualitative composition of the peptidoglycans the mutants belong to Streptomyces and are similar. Their glycan portion consists of equimolar quantities of N-acetyl glucosamine and muramic acid. The peptide subunit is presented by glutamic acid, L, L-diaminopimelic acid, glycine and alanine. The molar ratio of alanine is 1.2-1.3. The mutant strains differ in the content of carbohydrates, total phosphorus and phosphorus belonging to teichoic acids. Teichoic acids of the cell walls of the both strains are of the ribitolhosphate nature. The cell walls of the mutants contain polysaccharides differing from teichoic acids and consisting of glucose, galactose, arabinose and fucose. The influence of the cell wall composition of the mutant strains on their morphology and metabolism and comparison of the data relative to the mutant strains with those relative to the starting strain are discussed.

Amino Acids↗

PubMed1980

[Effect of K+ ions on Bac. polymyxa 153 growth and the biosynthesis of polymyxin B].

The growth of Bac. polymyxa, 153 producing polymyxin B did not change under the effect of various concentrations of potassium ions, while the antibiotic productivity of the cells significantly decreased. A great amount of polymyxin is excreted by the bacteria into the fermentation broth and a certain portion of the antibiotic remains in the cells. Under the experimental conditions the potassium salts slightly changed the pH value of the fermentation broth and probably did not affect polymyxin secretion from the cells into the fermentation broth.

Bacillus↗

PubMed1980

[Antibiotic action on Bacillus polymyxa 153 enzymatic activity].

The study on the effect of some antibiotics on the activity of pyruvate dehydrogenase (PDG) and dehydrogenases of the tricarboxylic acid cycle (TAC) in the cell extracts of Bac. polymyxa 153 producing polymyxin B showed that the level of the reaction of the individual enzymes to the effect of various antibiotics was different. Specific sensitivity to polymyxins M and B was found in succinate dehydrogenase and that to polymyxin B in malate dehydrogenase. The activity of the first components of the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes was completely suppressed not only by polymyxins M and B but also by novobiocin, ristomycin and nistatin. The activity of NADP-dependent isocitrate dehydrogenase was not suppressed by either of the antibiotics tested.

Anti-Bacterial Agents↗

PubMed1979

[Separation of the biosynthesis products of a mutant strain of Actinomyces chrysomallus var. carotenoides and the identification of actinomycin antibiotics].

An orange antibiotically active substance isolated from the mycelium of a mutant strain of Actinomyces chrysomallus var. carotenoides was identified as a mixture of actinomycins according to its light absorption spectra, circular dichroism spectra, IR spectra and chromatographic comparison with the standard samples. A scheme for successive extraction of the biologically active substances from the mycelium resulting in isolation of a fraction enriched with antibiotic substances and a fraction enriched with pigments is presented. A method for separation and purification of 3 groups of biologically active substances from the mycelium enriched extract was developed.

Antibiotics, Antineoplastic↗