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J. Bacteriol., Dec 1997, 7663-7670, Vol 179, No. 24
DW Wood, F Gong, MM Daykin, P Williams and LS Pierson 3rd
Pseudomonas aureofaciens 30-84 is a soilborne bacterium that colonizes the
wheat rhizosphere. This strain produces three phenazine antibiotics which
suppress take-all disease of wheat by inhibition of the causative agent
Gaeumannomyces graminis var. tritici. Phenazines also enhance survival of
30-84 within the wheat rhizosphere in competition with other organisms.
Expression of the phenazine biosynthetic operon is controlled by the
phzR/phzI N-acyl-homoserine lactone (AHL) response system (L. S. Pierson
III et al., J. Bacterial 176:3966-3974, 1994; D. W. Wood and L. S. Pierson
III, Gene 168:49-53, 1996). By using high- pressure liquid chromatography
coupled with high-resolution mass spectrometry, the AHL produced by PhzI
has now been identified as N- hexanoyl-homoserine lactone (HHL). In
addition, the ability of HHL to serve as an interpopulation signal molecule
in the wheat rhizosphere has been examined by using isogenic reporter
strains. Disruption of phzI reduced expression of the phenazine
biosynthetic operon 1,000-fold in the wheat rhizosphere. Coinoculation of
an isogenic strain which produced the endogenous HHL signal restored
phenazine gene expression in the phzI mutant to wild-type levels in situ.
These results demonstrate that HHL is required for phenazine expression in
situ and is an effective interpopulation signal molecule in the wheat
rhizosphere.
Copyright © 1997, American Society for Microbiology
N-acyl-homoserine lactone-mediated regulation of phenazine gene expression by Pseudomonas aureofaciens 30-84 in the wheat rhizosphere
Department of Plant Pathology, University of Arizona, Tucson 85721, USA.
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