title: Influence of fusaric acid on phenazine-1-carboxamide synthesis and gene expression of Pseudomonas chlororaphis strain PCL1391.
abstract: Production of the antifungal metabolite phenazine-1-carboxamide (PCN) by Pseudomonas chlororaphis strain PCL1391 is essential for the suppression of tomato foot and root rot caused by the soil-borne fungus F. oxysporum f. sp. radicis-lycopersici. The authors have shown previously that fusaric acid (FA), a phytotoxin produced by Fusarium oxysporum, represses the production of PCN and of the quorum-sensing signal N-hexanoyl-l-homoserine lactone (C(6)-HSL). Here they report that PCN repression by FA is maintained even during PCN-stimulating environmental conditions such as additional phenylalanine, additional ferric iron and a low Mg(2+) concentration. Constitutive expression of phzI or phzR increases the production of C(6)-HSL and abolishes the repression of PCN production by FA. Transcriptome analysis using P. chlororaphis PCL1391 microarrays showed that FA represses expression of the phenazine biosynthetic operon (phzABCDEFGH) and of the quorum-sensing regulatory genes phzI and phzR. FA does not alter expression of the PCN regulators gacS, rpoS and psrA. In conclusion, reduction of PCN levels by FA is due to direct or indirect repression of phzR and phzI. Microarray analyses identified genes of which the expression is strongly influenced by FA. Genes highly upregulated by FA are also upregulated by iron starvation in Pseudomonas aeruginosa. This remarkable overlap in the expression profile suggests an overlapping stress response to FA and iron starvation.
authors.affiliation: Leiden University, Institute of Biology, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
authors.forename: E Tjeerd
authors.initials: ET
authors.lastname: van Rij
authors.affiliation: Leiden University, Institute of Biology, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
authors.forename: Geneviève
authors.initials: G
authors.lastname: Girard
authors.affiliation: Leiden University, Institute of Biology, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
authors.forename: Ben J J
authors.initials: BJJ
authors.lastname: Lugtenberg
authors.affiliation: Leiden University, Institute of Biology, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
authors.forename: Guido V
authors.initials: GV
authors.lastname: Bloemberg
mesh_terms: D005669:Fusaric Acid / Q000494:pharmacology*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D005798:Genes, Bacterial; D018551:Solanum lycopersicum / Q000382:microbiology; D010572:Pest Control, Biological; D010619:Phenazines / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology; D011549:Pseudomonas / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D010619:Phenazines; C420923:phenazine-1-carboxamide; D005669:Fusaric Acid