JB Accepts, published online ahead of print on 22 September 2006

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J. Bacteriol. doi:10.1128/JB.00893-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Pip, a novel activator of phenazine biosynthesis in Pseudomonas chlororaphis PCL1391

Geneviève Girard^*, Sharief Barends, Sébastien Rigali, E. Tjeerd van Rij, Ben J. J. Lugtenberg, and Guido V. Bloemberg

Leiden University, Institute of Biology, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands; Leiden University, Leiden Institute of Chemistry, Department of Molecular Genetics, PO Box 9502, 2300 RA Leiden, The Netherlands

^* To whom correspondence should be addressed. Email: girardg79{at}yahoo.com,

Secondary metabolites are important factors for interactions between bacteria and other organisms. Pseudomonas chlororaphis PCL1391 produces the antifungal secondary metabolite phenazine-1-carboxamide (PCN) that inhibits growth of Fusarium oxysporum, the causing agent of tomato foot and root rot. Our previous work unraveled a cascade of genes regulating the PCN biosynthesis operon, phzABCDEFGH. Via a genetic screen, we identify in this study a novel TetR/AcrR regulator, named Pip (phenazine inducing protein), which is essential for PCN biosynthesis. Combination of a phenotypical characterization of a pip mutant, in trans complementation assays of various mutant strains, and electrophoretic mobility shift assays identified Pip as the fifth DNA-binding protein so far involved in regulation of PCN biosynthesis. In this regulatory pathway, Pip is positioned is downstream of PsrA (Pseudomonas sigma factor regulator) and the stationary-phase sigma-factor RpoS, while it is upstream of the quorum-sensing system PhzI/PhzR. These findings provide further evidence that the path leading to the expression of secondary metabolism gene-clusters in Pseudomonas species is highly complex.

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