Identification and characterization of gene cluster for synthesis of the polyketide antibiotic 2,4-diacetylphloroglucinol from Pseudomonas fluorescens Q2-87

The polyketide metabolite 2,4-diacetylphloroglucinol (2,4-DAPG) is produced by many strains of fluorescent Pseudomonas spp. with biocontrol activity a gainst soilborne fungal plant pathogens. Genes required for 2,4-DAPG synthe sis by P. fluorescens Q2-87 are encoded by a 6.5-kb fragment of genomic DNA that can transfer production of 2,4-DAPG to 2,4-DAPG-nonproducing recipien t Pseudomonas strains. In this study the nucleotide sequence was determined for the 6.5-kb fragment and flanking regions of genomic DNA from strain Q2 -87. Six open reading frames were identified, four of which (phlACBD) compr ise an operon that includes a set of three genes (phlACB) conserved between eubacteria and archaebacteria and a gene (phlD) encoding a polyketide synt hase with homology to chalcone and stilbene synthases from plants. The bios ynthetic operon is flanked on either side by phlE and phlF, which code resp ectively for putative efflux and regulatory (repressor) proteins. Expressio n in Escherichia coli of phlA, phlC, phlB, and phlD, individually or in com bination, identified a novel polyketide biosynthetic pathway in which PhlD is responsible for the production of monoacetylphloroglucinol (MAPG). PhlA, PhlC, and PhlB are necessary to convert MAPG to 2,4-DAPG, and they also ma y function in the synthesis of MAPG.