Regulation of production of the antifungal metabolite 2,4-diacetylphloroglucinol in Pseudomonas fluorescens F113:: genetic analysis of phlF as a transcriptional repressor

The antifungal metabolite 2,4-diacetylphloroglucinol plays a major role in the biocontrol capabilities of Pseudomonas fluorescens. The phloroglucinol biosynthetic locus of P. fluorescens F113 has been isolated previously, From nucleotide sequence data, a putative regulator gene (phlF) was identified upstream and divergently transcribed from the phlACBD phloroglucinol biosynthetic genes. PhlF shows similarity to various transcriptional repressors in the EMBL database and exhibits a helix-turn-helix motif in its amino acid sequence. phlF was cloned into an expression vector and the PhlF protein product was purified. Gel retardation experiments demonstrated PhlF to be a DNA-binding protein and showed that it binds to the phlA-phlF intergenic region. Introduction of phlF into P. fluorescens F113 in multiple copies resulted in repression of phloroglucinol production in this strain, This effect was mediated at the transcription level since the expression of a phloroglucinol biosynthetic gene fusion in this background was equally repressed, Furthermore, the inactivation of phlF results in derepression of phloroglucinol production in this strain.