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J. Bacteriol. doi:10.1128/JB.01587-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Altering the Ratio of Phenazines in Pseudomonas chlororaphis (aureofaciens) 30-84: Effects on Biofilm Formation and Pathogen Inhibition

Department of Plant Sciences, Division of Plant Pathology & Microbiology, The University of Arizona, Tucson, AZ 85721

^* To whom correspondence should be addressed. Email: Lsp{at}u.arizona.edu.

	Abstract

Pseudomonas chlororaphis strain 30-84 is a plant beneficial bacterium able to control take-all disease of wheat caused by the fungal pathogen Gaeumannomyces graminis var. tritici (Ggt). The production of phenazines (PZs) by strain 30-84 is the primary mechanism of pathogen inhibition, and contributes to the persistence of strain 30-84 in the rhizosphere. PZ production is regulated in part by the PhzR/PhzI quorum sensing (QS) system. Previous flow cell analyses demonstrated that QS and PZs are involved in biofilm formation in P. chlororaphis (26). P. chlororaphis produces mainly two PZs, phenazine carboxylic acid (PCA) and 2-hydroxy-phenazine carboxylic acid (2-OH-PCA). In the present study, we examined the effect of altering the ratio of PZs produced by P. chlororaphis on biofilm formation and pathogen inhibition. As part of this study, we generated derivatives of strain 30-84 that produced only PCA or over-produced 2-OH-PCA. Using flow cell assays, we found that these PZ-altered derivatives of strain 30-84 differed from the wild type in initial attachment, mature biofilm architecture, and dispersal from biofilms. For example, increased 2-OH-PCA production promoted initial attachment and altered the 3-dimensional structure of the mature biofilm relative to the wild type. Additionally, both alterations promoted thicker biofilm development and lowered dispersal rates compared to the wild type. The PZ-altered derivatives of strain 30-84 also differed in their ability to inhibit the fungal pathogen Ggt. Loss of 2-OH-PCA resulted in a significant reduction in the inhibition of Ggt. Our findings suggest that alterations in the ratios of antibiotic secondary metabolites synthesized by an organism may have complex and wide-ranging effects on its biology.

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