Role of Gluconic Acid Production in the Regulation of Biocontrol Traits of Pseudomonas fluorescens CHA0

ABSTRACT The rhizobacterium Pseudomonas fluorescens CHA0 promotes the growth of various crop plants and protects them against root diseases caused by pathogenic fungi. The main mechanism of disease suppression by this strain is the production of the antifungal compounds 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT). Direct plant growth promotion can be achieved through solubilization of inorganic phosphates by the production of organic acids, mainly gluconic acid, which is one of the principal acids produced by Pseudomonas spp. The aim of this study was to elucidate the role of gluconic acid production in CHA0. Therefore, mutants were created with deletions in the genes encoding glucose dehydrogenase (gcd) and gluconate dehydrogenase (gad), required for the conversion of glucose to gluconic acid and gluconic acid to 2-ketogluconate, respectively. These enzymes should be of predominant importance for rhizosphere-colonizing biocontrol bacteria, as major carbon sources provided by plant root exudates are made up of glucose. Our results show that the ability of strain CHA0 to acidify its environment and to solubilize mineral phosphate is strongly dependent on its ability to produce gluconic acid. Moreover, we provide evidence that the formation of gluconic acid by CHA0 completely inhibits the production of PLT and partially inhibits that of DAPG. In the Δgcd mutant, which does not produce gluconic acid, the enhanced production of antifungal compounds was associated with improved biocontrol activity against take-all disease of wheat, caused by Gaeumannomyces graminis var. tritici. This study provides new evidence for a close association of gluconic acid metabolism with antifungal compound production and biocontrol activity in P. fluorescens CHA0.

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Role of NADP-dependent and quinoprotein glucose dehydrogenases in gluconic acid production by Gluconobacter oxydans

Enzyme and Microbial Technology ◽

10.1016/0141-0229(89)90075-6 ◽

1989 ◽

Vol 11 (3) ◽

pp. 160-164 ◽

Cited By ~ 37

Author(s):

J.T. Pronk ◽

P.R. Levering ◽

W. Olijve ◽

J.P. van Dijken

Keyword(s):

Gluconic Acid ◽

Acid Production ◽

Gluconobacter Oxydans ◽

Gluconic Acid Production

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Identification and Manipulation of Soil Properties To Improve the Biological Control Performance of Phenazine-Producing Pseudomonas fluorescens

Applied and Environmental Microbiology ◽

10.1128/aem.69.6.3333-3343.2003 ◽

2003 ◽

Vol 69 (6) ◽

pp. 3333-3343 ◽

Cited By ~ 74

Author(s):

Bonnie H. Ownley ◽

Brion K. Duffy ◽

David M. Weller

Keyword(s):

Soil Properties ◽

Pseudomonas Fluorescens ◽

Soil Ph ◽

Ammonium Nitrogen ◽

Disease Suppression ◽

Gaeumannomyces Graminis ◽

Total Carbon ◽

Principal Component Factor Analysis ◽

Biocontrol Activity ◽

Take All

ABSTRACT Pseudomonas fluorescens 2-79RN10 protects wheat against take-all disease caused by Gaeumannomyces graminis var. tritici; however, the level of protection in the field varies from site to site. Identification of soil factors that exert the greatest influence on disease suppression is essential to improving biocontrol. In order to assess the relative importance of 28 soil properties on take-all suppression, seeds were treated with strain 2-79RN10 (which produces phenazine-1-carboxylate [PCA+]) or a series of mutants with PCA+ and PCA− phenotypes. Bacterized seeds were planted in 10 soils, representative of the wheat-growing region in the Pacific Northwest. Sixteen soil properties were correlated with disease suppression. Biocontrol activity of PCA+ strains was positively correlated with ammonium-nitrogen, percent sand, soil pH, sodium (extractable and soluble), sulfate-sulfur, and zinc. In contrast, biocontrol was negatively correlated with cation-exchange capacity (CEC), exchangeable acidity, iron, manganese, percent clay, percent organic matter (OM), percent silt, total carbon, and total nitrogen. Principal component factor analysis of the 16 soil properties identified a three-component solution that accounted for 87 percent of the variance in disease rating (biocontrol). A model was identified with step-wise regression analysis (R 2 = 0.96; Cp statistic = 6.17) that included six key soil properties: ammonium-nitrogen, CEC, iron, percent silt, soil pH, and zinc. As predicted by our regression model, the biocontrol activity of 2-79RN10 was improved by amending a soil low in Zn with 50 μg of zinc-EDTA/g of soil. We then investigated the negative correlation of OM with disease suppression and found that addition of OM (as wheat straw) at rates typical of high-OM soils significantly reduced biocontrol activity of 2-79RN10.

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