PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “host:pathogen interactions”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources
PubMed1990

Pathogen-host interaction.

Host defense, as it generally applies to humans, refers to the individual's ability to withstand infections. Human host defense mechanisms are numerous, diversified, complex, and often interdependent. The administration of drugs may influence some phases of immunocompetence mechanisms. The effect of several antimicrobial agents on organic defenses has been studied. The parameters considered were chemotaxis, phagocytosis, intracellular killing, superoxide-anion production, antibody production, lymphocyte subset behavior, and natural killer cell activity. Some antibacterial agents inhibit these parameters, whereas others can enhance some of these immune parameters to differing extents. Some antibacterial agents have a neutral effect on these parameters.

Anti-Bacterial Agents↗
PubMed2006

Genomic analysis of host-pathogen interaction between Fusarium graminearum and wheat during early stages of disease development.

Fusarium graminearum strains responsible for causing the plant disease Fusarium head blight vary greatly in their ability to cause disease and produce mycotoxins on wheat. With the goal of understanding fungal gene expression related to pathogenicity, three cDNA libraries were created by suppression subtractive hybridization using wheat heads inoculated with a highly aggressive strain and either water or a less aggressive strain of this pathogen. Eighty-four fungal genes expressed during initial disease development were identified. The probable functions of 49 of these genes could be inferred by bioinformatic analysis. Thirty-five ESTs had no known homologues in current databases and were not identified by ab initio gene prediction methods. These ESTs from infected wheat heads probably represent F. graminearum genes that previously were not annotated. Four genes represented in one of these libraries were selected for targeted gene replacement, leading to the characterization of a two-component response regulator homologue involved in pathogenicity of the fungus. The mutants for this gene showed reduced sporulation and delayed spread of Fusarium head blight on wheat.

Computational Biology↗
PubMed1969

Host-Pathogen Interactions: I. A Correlation Between alpha-Galactosidase Production and Virulence.

Resistance or susceptibility of Red Kidney, Pinto and Small White beans (Phaseolus vulgaris) to the alpha, beta, and gamma strains of Colletotrichum lindemuthianum was either confirmed or established. These fungal strains secrete alpha-galactosidase, beta-galactosidase and beta-xylosidase when grown on cell walls isolated from the hypocotyls of any of the above bean varieties. These enzymes effectively degrade cell walls isolated from susceptible 5-day old hypocotyls but degrade only slightly the walls isolated from resistant 18-day old hypocotyls. The amounts of the beta-galactosidase and beta-xylosidase secreted by the 3 fungal strains are relatively low and are approximately equivalent. The secretion of these 2 enzymes is not dependent upon the bean variety from which the hypocotyl cell walls used as a carbon source were isolated. However, the fungal strains secrete greater amounts of alpha-galactosidase when grown on hypocotyl cell walls isolated from susceptible plants than when grown on walls from resistant plants. Virulent isolates of the fungus, when grown on hypocotyl cell walls isolated from a susceptible plant, secrete more alpha-galactosidase than do attenuated (avirulent) isolates of the same fungal strain grown under the same conditions. The alpha-galactosidase secreted by each of the fungal strains is capable of removing galactose from the hypocotyl cell walls of each bean variety tested. Galactose is removed from the cell walls of each variety at the same rate regardless of whether the cell walls were isolated from a susceptible or resistant plant.

Journal Article↗
PubMed1971

Host-Pathogen Interactions: II. Parameters Affecting Polysaccharide-degrading Enzyme Secretion by Colletotrichum lindemuthianum Grown in Culture.

The effect of a number of physiological variables on the secretion of polysaccharide-degrading enzymes by culture-grown Colletotrichum lindemuthianum (Saccardo and Magnus) Scribner was determined. The number of spores used to inoculate cultures grown on isolated bean hypocotyl cell walls affects the time after inoculation at which enzyme secretion occurs, but has no significant effect on the maximal amount of enzyme ultimately secreted. Cell walls isolated from bean leaves, first internodes, or hypocotyls (susceptible to C. lindemuthianum infection), when used as carbon source for C. lindemuthianum growth, stimulate the fungus to secrete more alpha-galactosidase than do cell walls isolated from roots (resistant to infection). The concentration of carbon source used for fungal growth determines the final level of enzyme activity in the culture fluid. The level of enzyme secretion is not proportional to fungal growth; rather, enzyme secretion is induced. Maximal alpha-galactosidase activity in the culture medium is found when the concentration of cell walls used as carbon source is 1% or greater. A higher concentration of cell walls is necessary for maximal alpha-arabinosidase activity. Galactose, when used as the carbon source, stimulates alpha-galactosidase secretion but, at comparable concentrations, is less effective in doing so than are cell walls. Polysaccharide-degrading enzymes are secreted by C. lindemuthianum at different times during growth of the pathogen on isolated cell walls. Pectinase and alpha-arabinosidase are secreted first, followed by beta-xylosidase and cellulase, then beta-glucosidase, and, finally, alpha-galactosidase.

Journal Article↗
PubMed1973

Host-Pathogen Interactions: VI. A Single Plant Protein Efficiently Inhibits Endopolygalacturonases Secreted by Colletotrichum Lindemuthianum and Aspergillus Niger.

Endopolygalacturonases have been purified from the extracellular enzymes of Colletotrichum lindemuthianum and Aspergillus niger. A protein, purified from Red Kidney (Phaseolus vulgaris) beans for its ability to inhibit the endopolygalacturonase secreted by C. lindemuthianum, inhibits the A. niger endopolygalacturonase almost as efficiently as it inhibits the C. lindemuthianum enzyme.

Journal Article↗
PubMed1976

Host-Pathogen Interactions: IX. Quantitative Assays of Elicitor Activity and Characterization of the Elicitor Present in the Extracellular Medium of Cultures of Phytophthora megasperma var. sojae.

Resistance of soybean (Glycine max L.) seedlings to Phytophthora megasperma var. sojae (Pms) is in part due to the accumulation in infected tissue of a compound which is toxic to Pms. The accumulation of this compound, a phytoalexin called glyceollin, is triggered by infection, but it can also be triggered by molecules, "elicitors," present in cultures of Pms. The ability of the Pms elicitor to stimulate phytoalexin accumulation in soybean tissues has been used as the basis for biological assays of elicitor activity. Two bioassays were developed and characterized in this study of the Pms elicitor. These bioassays use the cotyledons and the hypocotyls of soybean seedlings. The cotyledon assay was used to characterize the extracellular Pms elicitor. This elicitor was isolated from Pms cultures and purified by ion exchange and molecular sieving chromatography. The extracellular Pms elicitor was determined to be a predominantly 3-linked glucan, which is similar in composition and structure to a polysaccharide component of Pms mycelial walls.

Journal Article↗
PubMed1976

Host-Pathogen Interactions: X. Fractionation and Biological Activity of an Elicitor Isolated from the Mycelial Walls of Phytophthora megasperma var. sojae.

An elicitor of phytoalexin production in soybean (Glycine max L.) tissues was isolated from purified Phytophthora megasperma var. sojae mycelial walls by a heat treatment similar to that used to solubilize the surface antigens from the cell walls of Saccharomyces cerevisiae. The wall-released elicitor is a discrete, minor portion of the P. megasperma var. sojae mycelial walls. The elicitor released from the mycelial walls was divided by diethylaminoethylcellulose and concanavalin A-Sepharose chromatography into four fractions, each having different chemical characteristics. The four fractions were obtained from each of the three races of P. megasperma var. sojae. The corresponding fractions from each of the three races are very similar in composition and elicitor activity. The results suggest that the elicitor activity of each fraction resides in the glucan component of the fraction. Evidence is presented to demonstrate that the elicitors are not race-specific and that the accumulation of glyceollin is not sufficient to account for race-specific resistance.

Journal Article↗
PubMed1976

Host-Pathogen Interactions: XII. Response of Suspension-cultured Soybean Cells to the Elicitor Isolated from Phytophthora megasperma var. sojae, a Fungal Pathogen of Soybeans.

The glucan elicitor isolated from the mycelial walls of Phytophthora megasperma var. sojae, the fungus which causes stem and root rot in soybeans, stimulates the activity of phenylalanine ammonia-lyase and the accumulation of glyceollin in suspension-cultured soybean cells. Nigeran, a commercially available fungal wall glucan, was the only other compound tested which has any activity in this system. Glyceollin is a phenylpropanoid-derived phytoalexin which is toxic to P. megasperma var. sojae. Evidence is presented to support the hypothesis that the action of elicitors in stimulating phytoalexin synthesis is not species or variety specific but, rather, is part of a general defensive response of plants.

Journal Article↗
PubMed1977

Host-Pathogen Interactions: XIII. Extracellular Invertases Secreted by Three Races of a Plant Pathogen Are Glycoproteins Which Possess Different Carbohydrate Structures.

The invertase present in the culture fluid of races 1, 2, and 3 of Phytophthora megasperma Drechs. var. sojae A. A. Hildebrand (Pms) were purified until they gave but a single band, whether stained for protein or carbohydrate, after isoelectric focusing in flat bed gels. The sugar compositions of multiple preparations of the purified invertases from each race of this fungal pathogen were determined by quantitative gas chromatography of their alditol acetates. The invertases are composed of about 25% carbohydrate. Mannose and glucosamine make up more than 97% of the carbohydrate portions of the invertases of all three Pms races analyzed, but the ratio of mannose to glucosamine is clearly not the same in each race. The glycosyl linkage compositions of the glucosamine-containing mannans of multiple preparations of the Pms invertases were determined by GC-MS analysis of the partially methylated alditol acetate derivatives. The results of these analyses demonstrate clear quantitative differences between the glycosyl components of the different Pms races. The existence of race-specific carbohydrate structures in the differentially virulent Pms races suggests that these carbohydrates may be involved in determining the specificity of hostpathogen interactions.

Journal Article↗
PubMed1978

Host-Pathogen Interactions: XIV. Isolation and Partial Characterization of an Elicitor from Yeast Extract.

An elicitor of glyceollin accumulation in soybeans (Glycine max L.) has been isolated from a commercially available extract of brewers' yeast. Yeast is not a known pathogen of plants. The elicitor was isolated by precipitation in 80% (v/v) ethanol followed by column chromatography on DEAE-cellulose, sulfopropyl-Sephadex, and concanavalin A-Sepharose. Compositional and structural analysis showed the elicitor to be a glucan containing terminal, 3-, 6-, and 3,6-linked glucosyl residues. The yeast elicitor stimulates the accumulation of glyceollin in the cotyledons and hypocotyls of soybeans when as little as 15 nanograms or 100 nanograms of the elicitor is applied to the respective tissues. The yeast elicitor is very similar in both structure and absolute elicitor activity to an elicitor isolated from the mycelial walls of Phytophthora megasperma var. sojae, a pathogen of soybeans. These and other results of this laboratory suggest that plants are able to respond to the presence of a wide range of fungi by recognizing, as foreign to the plant, structural polysaccharides of the mycelial walls of the fungi.

Journal Article↗
PubMed1978

Host-Pathogen Interactions: XV. Fungal Glucans Which Elicit Phytoalexin Accumulation in Soybean Also Elicit the Accumulation of Phytoalexins in Other Plants.

A beta-glucan isolated from the mycelial walls of Phytophthora megasperma var. sojae and a glucan purified from yeast extract stimulate the accumulation of phytoalexins in red kidney bean, Phaseolus vulgaris, and stimulate the accumulation of the phytoalexin, rishitin, in potato tubers, Solanum tuberosum. These glucans have previously been shown to be potent elicitors of glyceollin accumulation in soybean, Glycine max.Treatment of kidney bean cotyledons with the glucan elicitors resulted in the accumulation of at least five fungistatic compounds. These compounds migrate during thin layer chromatography identically to the fungistatic compounds which accumulate in kidney beans which have been inoculated with Colletotrichum lindemuthianum, a fungal pathogen of kidney beans.Potatoes accumulate as much as 29 micrograms of rishitin per gram fresh weight following exposure to the glucan from Phytophthora megasperma var. sojae and as much as 19.5 micrograms of rishitin per gram fresh weight following exposure to yeast glucan. Potatoes accumulated 28 micrograms of rishitin per gram fresh weight following inoculation with live Phytophthora megasperma var. sojae.

Journal Article↗
PubMed1981

Host-Pathogen Interactions: XVI. PURIFICATION AND CHARACTERIZATION OF A beta-GLUCOSYL HYDROLASE/TRANSFERASE PRESENT IN THE WALLS OF SOYBEAN CELLS.

The fact that fungal glucans will stimulate soybeans to accumulate phytoalexins prompted an investigation of soybean cell beta-1,3-glucanases and beta-glucosidases, as well as the ability of these enzymes to hydrolyze the fungal glucans. Several beta-1,3-glucanases and beta-glucosidases can be solubilized from the walls of suspension-cultured soybean cells by treatment with 1.0 molar sodium acetate buffer. An enzyme, which has been termed beta-glucosylase I, is the dominant beta-1,3-glucanase in the cell wall extracts. Utilizing CM-Sephadex chromatography, hydroxylapatite chromatography, and affinity chromatography, beta-glucosylase I has been purified 71-fold, with 39% recovery, from the mixture of cell wall enzymes. The affinity chromatography column material was prepared by covalently attaching p-aminophenyl-1-beta-d-glucopyranoside, an analog of a beta-glucosylase I substrate, to Sepharose. beta-Glucosylase I, purified by this procedure, yields a single band on isoelectric focusing gels (pH 8.9). However, the purified beta-glucosylase I yields a darkly-staining protein band at an apparent molecular weight of 69,000 and several lightly-staining protein bands in sodium dodecyl sulfate polyacrylamide gels. Additional purification procedures fail to remove these lightly-staining protein bands.beta-Glucosylase I will hydrolyze the beta-glucan substrates, laminarin (3-linked) and lichenan (3- and 4-linked), and therefore, possesses beta-glucanase activity. Studies of the progressive hydrolysis of laminarin by beta-glucosylase I demonstrate that the enzyme hydrolyzes polysaccharide substrates in an exo manner. beta-Glucosylase I will also hydrolyze a variety of low molecular weight beta-glucosides including various beta-linked diglucosides. Thus, beta-glucosylase I also possesses beta-glucosidase activity.Several lines of evidence are presented that the beta-glucanase and the beta-glucosidase activities exhibited by purified beta-glucosylase I preparations are catalyzed by the same enzyme. This evidence includes inhibition studies which indicate that the beta-glucanase and the beta-glucosidase activities of beta-glucosylase I are catalyzed at the same active site. beta-Glucosylase I will also catalyze glucosyl transfer. This catalytic activity is responsible for the observed ability of the enzyme to synthesize di- and trisaccharides from laminarin. The disaccharides formed by beta-glucosylase I-catalyzed transglucosylation are the beta-anomers of the 6-, 4-, 3-, and 2-linked diglucosides in the relative proportions of 10:1:1:1. The ability of beta-glucosylase I to catalyze glucosyl transfer indicates that beta-glucosylase I is biochemically more similar to previously studied beta-glucosidases than to beta-glucanases. This conclusion is supported by the observation that beta-glucosylase I is strongly inhibited by 1,5-d-gluconolactone, an inhibitor of beta-glucosidases but not of beta-glucanases.

Journal Article↗
PubMed1981

Host-Pathogen Interactions : XVII. HYDROLYSIS OF BIOLOGICALLY ACTIVE FUNGAL GLUCANS BY ENZYMES ISOLATED FROM SOYBEAN CELLS.

The ability of beta-glucosylase I, a soybean cell wall beta-glucosyl hydrolase, to degrade elicitors of phytoalexin accumulation was studied. Extensive beta-glucosylase I treatment of the glucan elicitor isolated from the mycelial walls of Phytophthora megasperma var. sojae results in hydrolysis of 77% of the glucosidic bonds of the elicitor and destruction of 94% of its activity. Soybean cell walls contain some additional factor, probably one or more additional enzymes, which can assist beta-glucosylase I in hydrolyzing the glucan elicitor. This was demonstrated by the more rapid hydrolysis of the glucan elicitor by a mixture of soybean cell wall enzymes (containing beta-glucosylase I). In a single treatment, the mixture of cell wall enzymes hydrolyzed 91% of the glucosidic bonds and destroyed 85% of the activity of the elicitor. The enzymes from soybean cell walls will also hydrolyze elicitor-active oligoglucosides prepared from the mycelial walls of Phytophthora megasperma var. sojae. The active oligoglucosides are more susceptible than the glucan elicitor to hydrolysis by these enzymes. The mixture of cell wall enzymes or beta-glucosylase I, by itself, hydrolyzes more than 96% of the glucosidic bonds and destroys more than 99% of the activity of the oligoglucoside elicitor. Two possible advantages for the existence of these enzymes in the walls of soybean cells are discussed.

Journal Article↗
PubMed1981

Host-Pathogen Interactions : XVIII. ISOLATION AND BIOLOGICAL ACTIVITY OF GLYCINOL, A PTEROCARPAN PHYTOALEXIN SYNTHESIZED BY SOYBEANS.

A previously unrecognized phytoalexin has been isolated from soybean cotyledons that had been infected with bacteria or exposed to ultraviolet light. The phytoalexin has been purified to homogeneity by silica gel flash chromatography and high pressure liquid chromatography. It has been structurally characterized by its ultraviolet, circular dichroism and nuclear magnetic resonance spectra, polarimetry, and its mass spectrometric fragmentation pattern. The phytoalexin, (6aS,11aS)-3,6a,9-trihydroxypterocarpan, is a compound that had previously been detected in CuCl(2)-treated soybeans and is structurally related to the previously identified soybean phytoalexins glycerollins I to IV. It is proposed that the trivial name glycinol be used for this phytoalexin. Glycinol is a broad spectrum antibiotic capable of prolonging the lag phase of growth of all six bacteria examined, namely Erwinia carotovora, Pseudomonas glycinea (races 1 and 3), Escherichia coli, Xanthomonas phaseoli, and Bacillus subtilis. Glycinol also inhibits the growth of the fungi Phytophthora megasperma f. sp. glycinea (race 1), Saccharomyces cerevisiae, and Cladosporium cucumerinum. Glycinol is a static agent against the six bacterial species listed above and against S. cerevisiae, and appears to be static against the other fungi examined. As with other phytoalexins, there is no correlation between the pathogenicity of a microorganism and its sensitivity to glycinol.

Journal Article↗
PubMed1981

Host-Pathogen Interactions : XIX. THE ENDOGENOUS ELICITOR, A FRAGMENT OF A PLANT CELL WALL POLYSACCHARIDE THAT ELICITS PHYTOALEXIN ACCUMULATION IN SOYBEANS.

An elicitor of phytoalexin accumulation (endogenous elicitor) is solubilized from purified cell walls of soybean (Glycine max [L.] Merr., cv. Wayne) by extracting the walls with hot water or by subjecting the walls to partial acid hydrolysis. The endogenous elicitor obtained from soybean cell walls binds to an anion exchange resin. The elicitor-active material released from the resin contains oligosaccharides rich in galacturonic acid; small amounts of rhamnose and xylose are also present. The preponderance of galacturonic acid in the elicitor-active fragments suggests that the elicitor is, in fact, a fragment of a pectic polysaccharide. This possibility is supported by the observation that treatment of the wall fragments with a highly purified endopolygalacturonase destroys their ability to elicit phytoalexin accumulation. This observation, together with other evidence presented in this paper, suggests that galacturonic acid is an essential constituent of the elicitor-active wall fragments. Endogenous elicitors were also solubilized by partial hydrolysis from cell walls of suspension-cultured tobacco, sycamore, and wheat cells.

Journal Article↗
PubMed1982

Host-Pathogen Interactions : XX. BIOLOGICAL VARIATION IN THE PROTECTION OF SOYBEANS FROM INFECTION BY PHYTOPHTHORA MEGASPERMA F. SP. GLYCINEA.

Phytophthora megasperma f.sp. glycinea, which causes soybean (Glycine max) root and stem rot, exists as several races which differ in their ability to infect a range of soybean cultivars. A glycoprotein-rich fraction (Fraction I) isolated from fungal culture fluid protects soybean seedlings from infection with compatible races. In an early study (13), seedlings were protected only by Fraction I purified from incompatible races. In 1979, seedlings were better protected by Fraction I isolated from incompatible races than by Fraction I isolated from compatible races. In 1980, seedlings were protected equally well by Fraction I from incompatible and compatible races. Materials similar in composition to Fraction I did not protect seedlings from infection. No cause could be identified for the apparent change, during the 3-year period, in the race specificity of the protection assay. Variability in the bioassay prohibited further purification or characterization of Fraction I components that protect seedlings from infection.

Journal Article↗