Molecular Plant-Microbe Interactions (2001) 14, 969-979

Thomas F.C. Chin-A-Woeng, Daan van den Broek, Gert de Voer, Koen M.G.M. van der Drift, Sietske Tuinman, Jane E. Thomas-Oates, Ben J.J. Lugtenberg and Guido V. Bloemberg (2001)
Phenazine-1-carboxamide production in the biocontrol strain Pseudomonas chlororaphis PCL1391 is regulated by multiple factors secreted into the growth medium
Molecular Plant-Microbe Interactions 14 (8), 969-979
Abstract: Pseudomonas chlororaphis PCL1391 controls tomato foot and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici. The production of phenazine-1-carboxamide (PCN) is crucial for this biocontrol activity. In vitro production of PCN is observed only at high-population densities, suggesting that production is under the regulation of quorum sensing. The main autoinducer molecule produced by PCL1391 was identified structurally as N-hexanoyl-L-homoserine lactone (C(6)-HSL). The two other autoinducers that were produced comigrate with N-butanoyl-L-homoserine lactone (C(4)-HSL) and N-octanoyl-L-homoserine lactone (C(8)-HSL). Two PCL1391 mutants lacking production of PCN were defective in the genes phzI and phzR, respectively, the nucleotide sequences of which were determined completely. Production of PCN by the phzI mutant could be complemented by the addition of exogenous synthetic C(6)-HSL, but not by C(4)-HSL, C(8)-HSL, or any other HSL tested. Expression analyses of Tn5luxAB reporter strains of phzI, phzR, and the phz biosynthetic operon clearly showed that phzI expression and PCN production is regulated by C(6)-HSL in a population density-dependent manner. The introduction of multiple copies of the regulatory genes phzI and phzR on various plasmids resulted in an increase of the production of HSLs, expression of the PCN biosynthetic operon, and consequently, PCN production, up to a sixfold increase in a copy-dependent manner. Surprisingly, our expression studies show that an additional, yet unidentified factor(s), which are neither PCN nor C(4)-HSL or C(8)-HSL, secreted into the growth medium of the overnight cultures, is involved in the positive regulation of phzI, and is able to induce PCN biosynthesis at low cell densities in a growing culture, resulting in an increase of PCN production.
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Link to article at publishers website
Database assignments for author(s): Ben J.J. Lugtenberg

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
molecular biology - genes

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Fusarium crown and root rot	Tomato (Solanum lycopersicum)
Pseudomonas chlororaphis (antagonist)	Fusarium crown and root rot	Tomato (Solanum lycopersicum)
	Fusarium oxysporum