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Biomedical subjects

I Chet

Publications and source records attributed to I Chet.

At least 55 records · Page 3Linked to original sources
PubMed1983

Ochratoxin A production by Aspergillus ochraceus Wilhelm grown under controlled atmospheres.

When Aspergillus ochraceus NRRL 3174 was grown under controlled atmospheres with 1 and 5% O2 and without CO2, the amount of ochratoxin produced was the same as that produced by the control colonies. Increasing the O2 level up to 40% reduced ochratoxin production by 75%, whereas at 60% O2, ochratoxin production was enhanced. In atmospheres enriched with 10 or 20% CO2, ochratoxin production was reduced when O2 concentrations were below 20% and enhanced when the O2 concentration was 40 or 60% O2. Ochratoxin production was completely inhibited at 30% CO2 and above, regardless of the O2 level. Colony growth was partially inhibited at 60% CO2, and no growth occurred at 80% CO2 or above. However, when colonies inhibited by 60% CO2 or above were subsequently exposed to air, radial growth, number of sclerotia formed, and the amount of ochratoxin produced were the same as in the control colonies. The results indicate that A. ochraceus is tolerant to CO2 concentrations higher than those required to control storage insects.

Aspergillus↗
PubMed1983

Possible role of lectins in mycoparasitism.

Lectin activity in a host-mycoparasite relationship was demonstrated with Rhizoctonia solani and Trichoderma harzianum. Attachment of O but not A and B erythrocytes to hyphae occurred on R. solani but not on its mycoparasite. This phenomenon, which was Ca2+ and Mn2+ dependent, was prevented by galactose, present in T. harzianum cell walls, and by fucose.

ABO Blood-Group System↗
PubMed1983

Ochratoxin production by Aspergillus ochraceus as affected by methionine and structurally related compounds.

When 10(-2) M of L- or D-methionine was added to a synthetic medium containing xylose as the sole carbon source, ochratoxin production by Aspergillus ochraceus was strongly inhibited. At that concentration methionine derivatives, e.g., alpha-methyl-DL-methionine, DL-methionine sulfoxide, and L-methionine sulfone, did not inhibit ochratoxin production, whereas DL-methionine S-methyl sulfonium chloride (MMSC) inhibited ochratoxin production to a large extent. L-Methionine, as well as MMSC, also completely inhibited sclerotia formation, while D-methionine and DL-methionine sulfoxide caused only a partial inhibition. At lower concentrations (10(-3) and 10(-4) M), none of the compounds exhibited inhibitory effects. In cases where strong ochratoxin inhibition was detected, fungal radial growth or mycelial dry weight was inhibited by only 10-25%, while the initial pH of the medium dropped from approximately 6.5 to approximately 4.4-5.0. Adjustment of the initial pH of media supplemented with 10(-2) M L-methionine, D-methionine, or MMSC to a pH of approximately 7.8 did not change the inhibitory effects on ochratoxin production in media containing L-methionine. On the other hand, sclerotia formation was restored in all three treatments.

Aspergillus↗
PubMed1981

Changes in the chemical composition of oospores of Pythium aphanidermatum during bimodal germination.

The developmental mode by which oospores of Pythium aphanidermatum germinate may be controlled by the concentration of glucose present in the germination medium. When incubated in a liquid medium containing emulsified lecithin without added glucose (S + L), oospores germinated indirectly, with zoospore release occurring during the 10th to 13th h. A decrease in dry weight of the fungus took place by the 13th h of indirect germination. When 0.2 mM glucose was added to S + L, the dry weight of germlings increased and direct germination occurred without zoospore formation. Polar lipid comprised the bulk of total acylglycerides of dormant oospores. A greater decrease in total fatty acid content took place during direct germination than during indirect germination. During both developmental modes of germination, polar lipid content decreased considerably; neutral lipids, however, increased during indirect germination and decreased during direct germination. Protein content of the fungus increased in both developmental modes of germination, being initially 9.7% of the dry weight of dormant oospores. After 13 h of incubation, KOH-soluble polysaccharide decreased by 35% during direct germination and by 48% during indirect germination.

Fatty Acids↗
PubMed1978

Quantitative assay for algal chemotaxis.

A quantitative capillary assay is described for measuring chemoreception in the neritic and littoral unicellular alga Dunaliella tertiolecta. Lucite chemotaxis plates were used in the assay with 3-microliter capillaries. A Coulter Counter was employed to determine algal cell numbers. D. tertiolecta is attracted to ammonium ion with a maximum positive response at 10(-3) M. Inclusion of calcium and L-methionine in the chemotaxis medium stimulates algal chemoreception, although neither chemical is essential for motility. Attraction of the chlorophyte to ammonium is dependent on time of incubation, cell density, and pH. The optimum pH for attraction was found to be 6.25.

Ammonium Chloride↗
PubMed1978

Localization of beta-(1,3)-glucanase in the mycelium of Sclerotium rolfsii.

The role of the lytic enzyme beta-(1,3)-glucanase in cell wall synthesis and its distribution in the mycelium of the fungus Sclerotium rolfsii were studied. Enzyme activity was determined after enzyme extraction with Triton X-100 from a cell wall preparation. Specific zones of immunofluorescence appeared in the hyphal tips, clamp connections, new septa, and lateral branching when a specific antiserum was used with the indirect method of the fluorescent antibody staining. Enzymatic activity in the cell wall preparation was inactivated by diethylpyrocarbonate. However, 69% of the total enzymatic activity was present in a latent form which was not affected by the ester. This result suggests that most of the beta-(1,3)-glucanase was present along the hyphal cell walls in a "masked" form. An active enzyme appeared only in those regions which showed immunofluorescence. The activity of glucan synthetase, an enzyme essential for wall formation, was higher in the branching funus grown on L-threonine-supplemented synthetic medium than in the synthetic medium-grown fungus.

Cell Wall↗
PubMed1977

Melanin biosynthesis during differentiation of Physarum polycephalum.

Melanin synthesis in the myxomycete Physarum polycephalum occurs during sporulation but not during spherule formation. Melanin-like pigment was extracted from spores. An almost identical substance of polyphenols was extracted from spherules and characterized by its ultraviolet and infrared absorbance spectra. Polyphenol oxidase activity in spherules was very low and showed only one weak isoenzyme band in isoelectric focusing polyacrylamide gels. A much higher activity, and an increasing number of isoenzymes, were detected in sporulating cultures after illumination during the differentiation process. The addition of melanin precursors resulted in the synthesis of brownish-yellow spherules, probably containing dopachrome, whereas the addition of polyphenol oxidase inhibitors resulted in yellow sporangia. The results indicate that melanin synthesis is probably only a stage in maturation but not an essential part of the morphogenetic process itself.

Catechol Oxidase↗
PubMed1977

A simple quantitative assay for bacterial motility.

It is argued that the average motility of bacterial populations should be identified with a diffusivity parameter. A simple capillary assay for quantifying this parameter is described, and some results obtained by using this procedure are presented. It is concluded that the assay combine speed and simplicity of operation with sufficient accuracy to make it a valuable tool in the assessment of motility.

Bacterial Physiological Phenomena↗
PubMed1977

The relationship between rhythmic hyphal growth and circadian formation of sclerotia in Sclerotium rolfsii Sacc.

The mycelium of the phytopathogenic fungus Sclerotium rolfsii type R (ATCC 26326) grown on a solid medium supplemented with 70 mM l-threonine exhibits a synchronous formation of sclerotia in circles whereas both leading and lateral hyphae enter into a rhythmic growth rate. A rhythmic activity of malate synthetase (malate synthase, EC 4.1.3.2) which accompanied the hyphal rhythm and preceded the formation of sclerotial circles was demonstrated. Both translocation of L-[14C]threonine and incorporation of L-[14C]leucine were significantly related to the circadian formation of sclerotia.

Circadian Rhythm↗
PubMed1977

Chemotaxis and movement of Physarum polycephalum and its responses to some neurotransmitters and psychomimetic compounds.

A method was developed for studying the effect of some neurotransmitters and drugs on the rate of movement and the chemotactic value of the plasmodium of Physarum polycephalum. Epinephrine (adrenaline) at a concentration of 1 mg/ml, reduced the rate of movement and shortened the length of the cycles of shuttle streaming, but did not affect the chemotactic response. The drugs DL-amphetamine, cannabinol and heroin diminished the rate of movement, whereas Na-barbitol misled the chemotactic response.

Amphetamine↗
PubMed1976

Metabolism of L-threonine and its relationship to sclerotium formation in Sclerotium rolfsii.

The activities of L-threonine dehydrogenase (I), 2-amino-3-oxybutyrate:CoA ligase (II), malate synthetase (III), isocitrate lyase (IV), glyoxylate dehydrogenase (V), glycine decarboxylase (VI), L-serine hydroxymethyltransferase (VII), glucan synthetase (VIII), glucose 6-phosphate dehydrogenase (IX) and succinic dehydrogenase (X) were detected in cell-free extracts prepared from the mycelium of the fungus Sclerotium rolfsii type R. Transfer of S. rolfsii to a threonine-containing medium resulted in a significant increase in the intracellular concentrations of L-threonine, glycine, serine and glyoxylate, and a decrease in oxalate. Incubation with 14C-labelled L-threonine resulted in an immediate output of 14CO2, and an accumulation of labelled glycine and serine in the mycelium. L-Threonine (10(-2)M) increased branching, favoured formation of sclerotia, and induced the formation of enzymes I to VIII, but not IX and X. Sodium oxalate (1-5 X 10(-2)M) inhibited branching, sclerotium formation and the activity of enzymes III and IV. Glycine (10(-1) M) inhibited branching, sclerotium formation and activity of I and II. Ammonium chloride (10(-1) to 10(-2) M) inhibited formation of sclerotia, threonine uptake and activity of III. Acetyl-CoA inhibited V and L-cysteine inhibited I as well as sclerotium formation and branching. It is suggested that hyphal morphogenesis and formation of sclerotia in S. rolfsii require an increased supply of carbohydrate intermediates and energy and that these are mainly supplied by the glyoxylate pathway.

Alcohol Oxidoreductases↗
PubMed1976

The relationship between chemical structure of attractants and chemotaxis by a marine bacterium.

The chemotactic responses of a marine pseudomonad to steroisomers and analogues of amino acids and sugars were tested. The data reveal that the bacterium is equally attracted to D, L, and DL forms of the amino acids. In contrastr, chemical analogues of the amino acids and glucose yielded significantly lower chemotactic responses. The threshold of bacterial detection was 10(-8) M for leucine and cysteine. However, the threshold molarity of most of the analogues was higher than those of the related amino acids and sugars.

Amino Acids↗
PubMed1975

The effect of alfalfa saponins on growth and lysis of Physarum polycephalum.

The prelytic events associated with the interaction of saponins with Physarum polycephalum membrane components were studied. It was found that alfalfa saponins form interaction products with membranal sterols, proteins and phospholipids. The interaction of saponins with proteins affect also certain membranal enzymic activities such as NADH oxidase and Malate dehydrogenase. It is suggested that although the interaction of the saponin with sterols is much more specific than with other membranal components, the lysis of plasmodia of P. polycephalum should be attributed to a concerted attack on the various membrane constituents. In continuation of these interactions, the changes of permeability of plasmodia membrane were expressed by increment of inorganic sodium ions and water influx, traced by lysis, while no efflux of ions was observed.

Cell Membrane↗
PubMed1975

Repulsion of bacteria from marine surfaces.

Organic compounds are capable of repelling motile bacteria from marine surfaces. The most effective compounds were acrylamide and benzoic and tannic acids. These were active at concentrations that were not toxic to the bacteria. Repellents were incorporated in nontoxic paints and applied to metal panels. Treated panels immersed in seawater developed a bacterial film of only 10(6) bacteria per cm6 after 12 days compared with untreated panels, which had 5 times 10(12) bacteria per cm2 after the same period. Field studies confirmed the effectiveness of these repellents. The use of biological repellents provides a new approach to the control of marine fouling.

Acrylamides↗
PubMed1975

Release of cell-bound polygalacturonase and cellulase from mycelium of Rhizoctonia solani.

Propagules of Rhizoctonia solani grown in modified Czapek's medium containing sodium polypectate or carboxymethyl cellulose as a sole carbon source produced both extracellular and cell-bound polygalacturonase (PG), and cellulase (Cx), respectively. The cell-bound enzymes can be released to various extents by shaking the germinating propagules in solutions of NaCl, KCl, phosphate buffer, Na2EDTA (ethylenediaminetetraacetate), detergents such as Triton X-100 (octyl phenoxypolyethoxyethanol), Tween 80 (polyoxyethylene sorbitan monooleate), Celmusol, and distilled water. Sodium dodecyl sulfate (SDS) inactivated both PG and Cx but did no affect Cx activity in phosphate buffer solution. PG was more easily released by salts from the mycelium of R. solani than Cx. The release of both enzymes was a passive process and was not due to an osmotic effect. The amount of the cell-bound fraction was correlated with the total amount of the extracellular fraction rather than with the mycelial growth. At least one-third of the cell-bound fractions of both enzymes was found to be associated with the cell wall fraction of the mycelium.

Cell Wall↗
PubMed1975

The effect of glucose and lactose on beta-D-galactosidase activity and formation of sclerotia in Sclerotium rolfsii.

Addition of 0.5% (w/v) lactose to a glucose-mineral mdeium (SM) induced formation of sclerotia and beta-D-galactosidase (beta-D-galactoside galactohydrolase)(EC 3.2.1.23) synthesis in Sclerotium rolfsii types A and R; These effects as well as lactose uptake were inversely related to glucose concentration within the tested range of 0.5 to 2.5% (w/v). Transfer of lactose-grown colonies to a glucose-supplemented medium nullified the inducible effect of lactose on formation of sclerotia, whereas transfer to water agar did not. It is concluded that glucose nullifies the effect of lactose on S. rolfsii by interfering with its active uptake.

Galactosidases↗