The effect of increased phenazine antibiotic production on the inhibition of economically important soilborne plant pathogens by pseudomonas a ureofaciens 3084
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Pseudomonas aureofaciens 3084 produces three phenazine antibiotics which are responsible for the ability of the strain to compete with the indigenous microflora in the rhizosphere. An additional consequence of phenazine production is the inhibition of several fungal plant pathogens in vitro. Phenazine production is regulated by a positive activator (PhzR) that acts in conjuction with a diffusable signal produced by Phzl. Introduction of additional copies of PhzR into strain 3084 resulted in ca. a five-fold increase in the level of phenazine production and increased the ability of strain 3084 to inhibit the growth of nine economically important fungal pathogens in vitro. Six of the nine fungal strains were inhibited significantly more in the presence of the over-producing strain. Gaeumannomyces graminis, was inhibited greater than 50%, regardless of the level of phenazines produced. The addition of a specific carbon source in Kanner medium (medium B) enhanced pigment production and inhibition of the fungal strains as compared to 1/5 potato dextrose agar medium (medium A), consistent with the proposed role of nutrients in the regulation of phenazine biosynthesis. The sclerotia formation of Sclerotinia sclerotiorum was 0% in the presence of strain 3084 and strain 3085 on medium B. However, 3084 could not significantly reduce sclerotia formation on medium A, where less phenazine pigments were produced. In greenhouse cone assays, 3084 significantly reduced disease incidence and disease severity. The phenazine deficient mutant strain 3084 Z, was significantly less effective in cone assay experiments. 1999, Taylor & Francis Group, LLC.
