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PubMed1982

Host-Pathogen Interactions : XXI. Extraction of a Heat-Labile Elicitor of Phytoalexin Accumulation from Frozen Soybean Stems.

An extract of frozen and thawed soybean (Glycine max L. Merr. cv. Wayne) stems is active, in wounded soybean cotyledons, as a heat-labile elicitor of phytoalexins. The elicitor activity of the extract is destroyed by heating to 95 degrees C for 10 minutes. The fraction that contains heat-labile elicitor activity releases heat-stable elicitor-active molecules from purified soybean cell walls. Heat-labile elicitor activity voids a Bio-Gel P-6 column and can be absorbed onto and eluted from a DEAE Sephadex ion exchange column. Using the cotyledon phytoalexin elicitor assay, maximum heatlabile elicitor activity was obtained when soybean stems were extracted with acetate buffer at pH 6.0. Addition of 1 millimolar CaCl(2) increased apparent heat-labile elicitor activity. The heat-labile elicitor stimulated maximum phytoalexin accumulation when applied to cotyledons immediately after the cotyledons were cut. Partially purified stem extracts lost heat-labile elicitor activity during storage for several days at 3 degrees C. The possible role of a heat-labile elicitor in stimulation of phytoalexin accumulation by both abiotic and biotic elicitors is discussed.

Journal Article↗
PubMed1983

Host-Pathogen Interactions : XXII. A Galacturonic Acid Oligosaccharide from Plant Cell Walls Elicits Phytoalexins.

Elicitors of phytoalexin accumulation in soybean (Glycine max L. Merr., cv Wayne) cotyledons were released from soybean cell walls and from citrus pectin by partial acid hydrolysis. These two hydrolysates yielded nearly identical distributions of elicitor activity when fractionated on anion-exchange columns. Chromatography of the pectin elicitor on gel filtration and high-pressure anion-exchange columns did not further purify the elicitor. Elicitor activity of the preparation was lost by treatment with either endo-alpha-1,4-polygalacturonase or pectate lyase. Glycosyl residue compositions of the purified elicitors from cell walls and pectin were both found to be approximately 98% galacturonosyl residues. Linkage analysis of the pectin elicitor showed that most, if not all, of the galacturonosyl residues were alpha-1,4-linked. The high-mass molecular ions detected by fast atom bombardment-mass spectrometry of the most active elicitor fractions from cell walls and pectin both corresponded precisely to a molecule composed of 12 galacturonosyl residues. These results suggest that dodeca-alpha-1,4-d-galacturonide is the active elicitor, but the possibility remains that the active component could be a slightly modified oligogalacturonide present, but not detected, in the purified fractions.

Journal Article↗
PubMed1983

Host-Pathogen Interactions : XXIII. The Mechanism of the Antibacterial Action of Glycinol, a Pterocarpan Phytoalexin Synthesized by Soybeans.

The biochemical basis for the ability of the pterocarpan phytoalexin glycinol (3,6a,9-trihydroxypterocarpan) to inhibit the growth of bacteria was examined. Glycinol at bacteriostatic concentrations (e.g. 50 micrograms per milliliter) inhibits the ability of Erwinia carotovora to incorporate [(3)H]leucine, [(3)H]thymidine, or [(3)H]uridine into biopolymers. Exposure of Escherichia coli membrane vesicles to glycinol at 20 micrograms per milliliter results in inhibition of respiration-linked transport of [(14)C]lactose and [(14)C]glycine into the vesicles when either d-lactate or succinate is supplied as the energy source. The ability of E. coli membrane vesicles to transport [(14)C]alpha-methyl glucoside, a vectorial phosphorylation-mediated process, is also inhibited by glycinol at 20 micrograms per milliliter. Furthermore, exposure of membrane vesicles to glycinol (50 micrograms per milliliter) at 20 degrees C results in the leakage of accumulated [(14)C]alpha-methyl glucoside-6-phosphate. The effects of the phytoalexins glyceollin, capsidiol, and coumestrol, and daidzein, a compound structurally related to glycinol but without antibiotic activity, upon the E. coli membrane vesicle respiration-linked transport of [(14)C]glycine and of [(14)C]alpha-methyl glucoside was also examined. Glyceollin and coumestrol (50 micrograms per milliliter), but not daidzein, inhibit both membrane-associated transport processes. These data imply that the antimicrobial activity of glycinol, glyceollin, and coumestrol are due to a general interaction with the bacterial membrane. Capsidiol (50 micrograms per milliliter) inhibits d-lactate-dependent transport of [(14)C]glycine but not vectorial phosphorylation-mediated transport of [(14)C]alpha-methyl glucoside. Thus, capsidiol's mechanism of antimicrobial action seems to differ from that of the other phytoalexins examined.

Journal Article↗
PubMed1983

Host-Pathogen Interactions : XXIV. Fragments Isolated from Suspension-Cultured Sycamore Cell Walls Inhibit the Ability of the Cells to Incorporate [C]Leucine into Proteins.

A bioassay to measure the incorporation of [(14)C]leucine into acid-precipitable polymers of suspension-cultured sycamore (Acer pseudoplatanus L.) cells is described. Using this assay, cell wall fragments solubilized from sycamore cell walls by partial acid hydrolysis are shown to contain components that inhibit the incorporation of [(14)C]leucine into the acid-precipitable polymers. This inhibition was not attributable to a suppression of [(14)C]leucine uptake. The effectiveness of the wall fragments in inhibiting [(14)C]leucine incorporation was substantially relieved by plasmolysis of the cells. Fragments released from starch and citrus pectin are shown not to possess such inhibitory activities.

Journal Article↗
PubMed1984

Host-Pathogen Interactions : XXV. Endopolygalacturonic Acid Lyase from Erwinia carotovora Elicits Phytoalexin Accumulation by Releasing Plant Cell Wall Fragments.

Heat-labile elicitors of phytoalexin accumulation in soybeans (Glycine max L. Merr. cv Wayne) were detected in culture filtrates of Erwinia carotovora grown on a defined medium containing citrus pectin as the sole carbon source. The heat-labile elicitors were highly purified by cation-exchange chromatography on a CM-Sephadex (C-50) column, followed by agarose-affinity chromatography on a Bio-Gel A-0.5m gel filtration column. The heat-labile elicitor activity co-purified with two alpha-1,4-endopolygalacturonic acid lyases (EC 4.2.2.2). Endopolygalacturonic acid lyase activity appeared to be necessary for elicitor activity because heat-inactivated enzyme preparations did not elicit phytoalexins. The purified endopolygalacturonic acid lyases elicited pterocarpan phytoalexins at microbial-inhibitory concentrations in the soybean-cotyledon bioassay when applied at a concentration of 55 nanograms per milliliter (1 x 10(-9) molar). One of these lyases released heat-stable elicitors from soybean cell walls, citrus pectin, and sodium polypectate. The heat-stable elicitor-active material solubilized from soybean cell walls by the lyase was composed of at least 90% (w/v) uronosyl residues. These results demonstrate that endopolygalacturonic acid lyase elicits phytoalexin accumulation by releasing fragments from pectic polysaccharides in plant cell walls.

Journal Article↗
PubMed1986

Host-Pathogen Interactions : XXIX. Oligogalacturonides Released from Sodium Polypectate by Endopolygalacturonic Acid Lyase Are Elicitors of Phytoalexins in Soybean.

Recent studies have demonstrated that an apparently homogeneous preparation of an alpha-1,4-d-endopolygalacturonic acid lyase (EC 4.2.2.2) isolated from the phytopathogenic bacterium Erwinia carotovora induced phytoalexin accumulation in cotyledons of soybean (Glycine max [L.] Merr. cv Wayne) and that this pectin-degrading enzyme released heat-stable elicitors of phytoalexins from soybean cell walls, citrus pectin, and sodium polypectate (KR Davis et al. 1984 Plant Physiol 74: 52-60). The present paper reports the purification, by anion-exchange chromatography on QAE-Sephadex columns followed by gel-permeation chromatography on a Bio-Gel P-6 column, of the two fractions with highest specific elicitor activity present in a crude elicitor-preparation obtained by lyase treatment of sodium polypectate. Structural analysis of the fraction with highest specific elicitor activity indicated that the major, if not only, component was a decasaccharide of alpha-1,4-d-galactosyluronic acid that contained the expected product of lyase cleavage, 4-deoxy-beta-l-5-threohexopyranos-4-enyluronic acid (4,5-unsaturated galactosyluronic acid), at the nonreducing terminus. This modified decagalacturonide fraction exhibited half-maximum and maximum elicitor activity at 1 microgram/cotyledon (6 micromolar) and 5 micrograms/cotyledon (32 micromolar) galactosyluronic acid equivalents, respectively. Reducing 90 to 95% of the carboxyl groups of the galactosyluronic acid residues abolished the elicitor activity of the decagalacturonide fraction. The second most elicitor-active fraction contained mostly undeca-alpha-1,4-d-galactosyluronic acid that contained 4,5-unsaturated galactosyluronic acid at the nonreducing termini. This fraction exhibited half-maximum and maximum elicitor activity at approximately 3 micrograms/cotyledon (17 micromolar) and 6 micrograms/cotyledon (34 micromolar) galactosyluronic acid equivalents, respectively. These results confirm and extend previous observations that oligogalacturonides derived from the pectic polysaccharides of plant cell walls can serve as regulatory molecules that induce phytoalexin accumulation in soybean. These results are consistent with the hypothesis that oligogalacturonides play a role in disease resistance in plants.

Journal Article↗
PubMed1989

Host-Pathogen Interactions : XXXIII. A Plant Protein Converts a Fungal Pathogenesis Factor into an Elicitor of Plant Defense Responses.

This paper describes the effect of a plant-derived polygalacturonase-inhibiting protein (PGIP) on the activity of endopolygalacturonases isolated from fungi. PGIP's effect on endopolygalacturonases is to enhance the production of oligogalacturonides that are active as elicitors of phytoalexin (antibiotic) accumulation and other defense reactions in plants. Only oligogalacturonides with a degree of polymerization higher than nine are able to elicit phytoalexin synthesis in soybean cotyledons. In the absence of PGIP, a 1-minute exposure of polygalacturonic acid to endopolygalacturonase resulted in the production of elicitor-active oligogalacturonides. However, the enzyme depolymerized essentially all of the polygalacturonic acid substrate to elicitor-inactive oligogalacturonides within 15 minutes. When the digestion of polygalacturonic acid was carried out with the same amount of enzyme but in the presence of excess PGIP, the rate of production of elicitor-active oligogalacturonides was dramatically altered. The amount of elicitor-active oligogalacturonide steadily increased for 24 hours. It was only after about 48 hours that the enzyme converted the polygalacturonic acid into short, elicitor-inactive oligomers. PGIP is a specific, reversible, saturable, high-affinity receptor for endopolygalacturonase. Formation of the PGIP-endopolygalacturonase complex results in increased concentrations of oligogalacturonides that activate plant defense responses. The interaction of the plant-derived PGIP with fungal endopolygalacturonases may be a mechanism by which plants convert endopolygalacturonase, a factor important for the virulence of pathogens, into a factor that elicits plant defense mechanisms.

Journal Article↗
PubMed1989

Adhesion of colonization factor antigen II-positive enterotoxigenic Escherichia coli strains to human enterocytelike differentiated HT-29 cells: a basis for host-pathogen interactions in the gut.

Enterotoxigenic Escherichia coli are the most common cause of travelers' and infant diarrhea in less-developed countries. In the present work, among several metabolically labeled human diarrheagenic E. coli strains, enterotoxigenic strains expressing colonization factor antigen II were shown to bind to HT-29 intestinal cell monolayers when these cells were grown in conditions promoting their enterocytic differentiation. Indirect immunofluorescence with fimbrial antisera revealed that pathogen attachment was associated with the production of a specific bacterial adhesin, the E. coli surface antigen CS3. Scanning and transmission electron micrographs showed an apical pattern of colonization, characteristic of enterotoxigenic E. coli infections. The above data were consistent with all observations previously made with human enterocytes obtained from intestinal biopsies. The lectin-carbohydrate nature of this cell-cell recognition mechanism was also established. Bacterial binding to differentiated HT-29 cells was inhibited by a mixture of newborn meconium glycopeptides. By coating the cell layers with the plant agglutinin from Evonymus europaea, pathogen attachment was also prevented. Binding of 125I-labeled CS3 adhesin and E. europaea agglutinin to brush border membrane proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to nitrocellulose revealed three bands of about 30, 20, and 13 kilodaltons, which acted as receptors for both bacterial and plant lectins. These data suggest that the sugar units to which the bacterial colonization factor CS3 binds are synthesized as carbohydrate chains of three brush border membrane glycoproteins in HT-29 cells by a differentiation-specific pathway.

Antigens, Bacterial↗
PubMed2000

Candida albicans RIM101 pH response pathway is required for host-pathogen interactions.

The ability of Candida albicans to respond to diverse environments is critical for its success as a pathogen. The RIM101 pathway controls gene expression and the yeast-to-hyphal transition in C. albicans in response to changes in environmental pH in vitro. In this study, we found that the RIM101 pathway is necessary in vivo for pathogenesis. First, we show that rim101(-)/rim101(-) and rim8(-)/rim8(-) mutants have a significant reduction in virulence using the mouse model of hematogenously disseminated systemic candidiasis. Second, these mutants show a marked reduction in kidney pathology. Third, the rim101(-)/rim101(-) and rim8(-)/rim8(-) mutants show defects in the ability to damage endothelial cells in situ. Finally, we show that an activated allele of RIM101, RIM101-405, is a suppressor of the rim8(-) mutation in vivo as it rescues the virulence, histological, and endothelial damage defects of the rim8(-)/rim8(-) mutant. These results demonstrate that the RIM101 pathway is required for C. albicans virulence in vivo and that the function of Rim8p in pathogenesis is to activate Rim101p.

Animals↗
PubMed2003

Correlation of acetate catabolism and growth yield in Staphylococcus aureus: implications for host-pathogen interactions.

Recently, we reported that the prototypical Staphylococcus aureus strain RN6390 (a derivative of NCTC 8325) had significantly reduced aconitase activity relative to a diverse group of S. aureus isolates, leading to the hypothesis that strain RN6390 has impaired tricarboxylic acid (TCA) cycle-mediated acetate catabolism. Analysis of the culture supernatant from RN6390 confirmed that acetate was incompletely catabolized, suggesting that the ability to catabolize acetate can be lost by S. aureus. To test this hypothesis, we examined the carbon catabolism of the S. aureus strains whose genome sequences are publicly available. All strains catabolized glucose and excreted acetate into the culture medium. However, strains NCTC 8325 and N315 failed to catabolize acetate during the postexponential growth phase, resulting in significantly lower growth yields relative to strains that catabolized acetate. Strains NCTC 8325 and RN6390 contained an 11-bp deletion in rsbU, the gene encoding a positive regulator of the alternative sigma factor sigma(B) encoded by sigB. An isogenic derivative strain of RN6390 containing the wild-type rsbU gene had significantly increased acetate catabolism, demonstrating that sigma(B) is required for acetate catabolism. Taken together, the data suggest that naturally occurring mutations can alter the ability of S. aureus to catabolize acetate, a surprising discovery, as TCA cycle function has been demonstrated to be involved in the virulence, survival, and persistence of several pathogenic organisms. Additionally, these mutations decrease the fitness of S. aureus by reducing the number of progeny placed into subsequent generations, suggesting that in certain situations a decreased growth yield is advantageous.

Acetic Acid↗
PubMed2004

Host-pathogen interaction during pneumococcal infection in patients with chronic obstructive pulmonary disease.

Acute exacerbation is a frequent complication of chronic obstructive pulmonary disease (COPD). Recent studies suggested a role for bacteria such as Streptococcus pneumoniae in the development of acute exacerbation. For this study, we investigated the following in COPD patients: (i) the epidemiology of pneumococcal colonization and infection, (ii) the effect of pneumococcal colonization on the development of exacerbation, and (iii) the immunological response against S. pneumoniae. We cultured sputa of 269 COPD patients during a stable state and during exacerbation of COPD and characterized 115 pneumococcal isolates by use of serotyping. Moreover, we studied serum immunoglobulin G (IgG) antibody titers, antibody avidities, and functional antibody titers against the seven conjugate vaccine serotypes in these patients. Colonization with only pneumococci (monocultures) increased the risk of exacerbation, with a hazard ratio of 2.93 (95% confidence interval, 1.41 to 6.07). The most prevalent pneumococcal serotypes found were serotypes 19F, 3, 14, 9L/N/V, 23A/B, and 11. We calculated the theoretical coverage for the 7- and 11-valent pneumococcal vaccines to be 60 and 73%, respectively. All patients had detectable IgG levels against the seven conjugate vaccine serotypes. These antibody titers were significantly lower than those in vaccinated healthy adults. Finally, on average, a 2.5-fold rise in serotype-specific and functional antibodies in S. pneumoniae-positive sputum cultures was observed during exacerbation. Our data indicate that pneumococcal colonization in COPD patients is frequently caused by vaccine serotype strains. Moreover, pneumococcal colonization is a risk factor for exacerbation of COPD. Finally, our findings demonstrate that COPD patients are able to mount a significant immune response to pneumococcal infection. COPD patients may therefore benefit from pneumococcal vaccination.

Adult↗
PubMed1995

Purification, characterization, and genetic analysis of Mycobacterium tuberculosis urease, a potentially critical determinant of host-pathogen interaction.

Mycobacterium tuberculosis urease (urea amidohydrolase [EC 3.5.1.5]) was purified and shown to contain three subunits: two small subunits, each approximately 11,000 Da, and a large subunit of 62,000 Da. The N-terminal sequences of the three subunits were homologous to those of the A, B, and C subunits, respectively, of other bacterial ureases. M. tuberculosis urease was specific for urea, with a Km of 0.3 mM, and did not hydrolyze thiourea, hydroxyurea, arginine, or asparagine. The enzyme was active over a broad pH range (optimal activity at pH 7.2) and was remarkably stable against heating to 60 degrees C and resistant to denaturation with urea. The enzyme was not inhibited by 1 mM EDTA but was inhibited by N-ethylmaleimide, hydroxyurea, acetohydroxamate, and phenylphosphorodiamidate. Urease activity was readily detectable in M. tuberculosis growing in nitrogen-rich broth, but expression increased 10-fold upon nitrogen deprivation, which is consistent with a role for the enzyme in nitrogen acquisition by the bacterium. The gene cluster encoding urease was shown to have organizational similarities to urease gene clusters of other bacteria. The nucleotide sequence of the M. tuberculosis urease gene cluster revealed open reading frames corresponding to the urease A, B, and C subunits, as well as to the urease accessory molecules F and G.

Amino Acid Sequence↗
PubMed2002

Host-pathogen interactions: the seduction of molecular cross talk.

Bacterial pathogens have evolved two major strategies to colonise the intestinal epithelium. Adherent microorganisms bind to the apical pole of the intestinal epithelium, whereas invasive microorganisms disrupt and invade the epithelium. Recognition of the genetic bases of bacterial pathogenicity and analysis of the molecular cross talks established between pathogens and their mammalian target cells have illuminated this diversity of interactions. We have compared the strategies of enteroinvasive pathogens, with emphasis on bacterial species such as Shigella, Yersinia, and Salmonella, that represent paradigms of interaction. Cross talks leading to alteration of the epithelial cell actin cytoskeleton appear as a recurrent theme during entry and dissemination into epithelial cells. Other cross talks alter the trafficking of cellular vesicles and induce changes in the intracellular compartment in which they reside, thus creating niches favourable to bacterial survival and growth. Finally, a variety of strategies also exist to deal with other components of the epithelial barrier, such as macrophages. Pro-phagocytic, anti-phagocytic, and pro-apoptotic processes appear to be of particular importance.

Actins↗