Host-Pathogen Interactions

Abstract

The biochemical basis for the ability of the pterocarpan phytoalexin glycinol (3,6a,9-trihydroxypterocarpan) to inhibit the growth of bacteria was examined. Glycinol 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 -lactate-dependent transport of I14CIglycine but not vectorial phosphorylation-mediated transport of 114CIa-methyl glucoside. Thus, capsidiors mechanism of antimicrobial action seems to differ from that of the other phytoalexins examined.Phytoalexins are low-mol-wt antibiotics produced by plants in response to various biotic and abiotic elicitors (1, 2,20,27,31,39 glycinol may inhibit the growth of widely diverse microorganisms by a similar mechanism of action (45).Previous studies on the mechanism of action of structurally diverse phytoalexins have implicated the membrane as the site of antimicrobial action (19,23,29,30,34,42). The research detailed in this paper was undertaken to determine the locus of action of glycinol. A comparison ofglycinol's effect on bacterial membranes with the effect on the membranes of other phytoalexins has allowed us to examine the question of whether the mode of action of glycinol is representative of other phytoalexins. (i-z-y+a ), a gift of Dr. R. Kaback, Roche Institute of Molecular Biology, Nutley, NJ, was maintained on nutrient agar (Difco) slants and plates. The E. coli used in the preparation of membrane vesicles was grown on Escherichia medium 63 (9). MATERIALS AND METHODS Materials. L-General. Liquid culture assays of the ability of glycinol to inhibit bacterial growth were performed as described (45). Glycinol concentrations were determined by A at 287 nm in absolute ethanol (Es7 = 5800). Membrane vesicles were prepared from E.coli following the method of Kaback (14), except that a 20-cc syringe equipped with an 18-gauge needle, rather than a Teflon and glass homogenizer, was used for resuspension of the membrane pellet (H. R. Kaback, personal communication). The membrane-vesicle preparations were shown to be free of bacterial contamination by incubation on nutrient agar. Protein concentrations were determined by the procedure of Bradford (7)

Isoflavonoid-inducible resistance to the phytoalexin glyceollin in soybean rhizobia

“…Therefore, it appears that the inhibition of specific target enzymes might be the primary mode of the antibiotic effect of glyceollin. However, as shown in the present study, glyceollin-resistant B. japonicum cells tolerate concentrations of glyceollin up to 440 ,M. Such high concentrations have been reported to disturb membrane integrity (44).…”

“…While some results suggest a nonspecific mode of action involving disruption of membrane integrity (44), other data support the hypothesis that glyceollin works via specific sensitive target enzymes such as ATPase (12) or NADH-ubiquinone-oxidoreductase (2). From unpublished data, we know that the NADH-ubiquinone-oxidoreductase of B. japonicum 110spc4 is highly sensitive to glyceollin, being strongly affected at concentrations as low as 2 ,uM.…”

“…From unpublished data, we know that the NADH-ubiquinone-oxidoreductase of B. japonicum 110spc4 is highly sensitive to glyceollin, being strongly affected at concentrations as low as 2 ,uM. The nonspecific membrane effects of glyceollin were observed at much higher concentrations (44). Therefore, it appears that the inhibition of specific target enzymes might be the primary mode of the antibiotic effect of glyceollin.…”

Characterization and virulence properties of Erwinia chrysanthemi lipopolysaccharide-defective, phi EC2-resistant mutants

“…The loss of virulence of some mutants could result either from the disappearance of a structure (LPS) protecting the bacterium from potential defense mechanism or allowing the initial stage of the disease, or from the appearance of a structure (LPS) able to elicit plant defense response. In the first context, some rough mutants, like the two avirulent mutants, might be more susceptible to antimicrobial agents (20) such as phytoalexins (25,35) or might be enhanced in the release of some signal able to induce such host defetse mechanisms (7). Alternatively, exposure of a specific portion of the LPS might allow it to serve as bacterial receptor (or signal) for some plant factor(s) (as lectins for instance), resulting then in drastic bacterial agglutination (30).…”

Effects of glyceollin on mRNA expression in the female mouse brain.

“…Subsequent studies showed that Glys potentially exhibit their antibacterial effects by inhibiting cellular processes and altering the structural integrity of bacterial membranes, thereby impeding bacterial growth (Weinstein and Albersheim 1983).…”