Reciprocal regulation of pyoluteorin production with membrane transporter gene expression in Pseudomonas fluorescens Pf-5

Pyoluteorin is a chlorinated polyketide antibiotic secreted by the rhizosphere bacterium Pseudomonas fluorescens Pf-5. Genes encoding enzymes and transcriptional regulators involved in pyoluteorin production are clustered in the genome of Pf-5. Sequence analysis of genes adjacent to the known pyoluteorin biosynthetic gene cluster revealed the presence of an ABC transporter system. We disrupted two putative ABC transporter genes by inserting transcriptional fusions to an ice nucleation reporter gene. Mutations in pltI and pltJ, which are predicted to encode a membrane fusion protein and an ATP-binding cassette of the ABC transporter, respectively, greatly reduced pyoluteorin production by Pf-5. During the transition from exponential growth to stationary phase, populations of a pltI mutant were lower than those of a pltI⁺ strain in a culture medium containing pyoluteorin, suggesting a role for the transport system in efflux and the resistance of Pf-5 to the antibiotic. Although pltI or pltJ mutant strains displayed low pyoluteorin production, they did not accumulate proportionately more of the antibiotic intracellularly, indicating that pltI and pltJ do not encode an exclusive exporter for pyoluteorin. Transcription of the putative pyoluteorin efflux genes pltI and pltJ was enhanced by exogenous pyoluteorin. These new observations parallel an earlier finding that pyoluteorin enhances the transcription of pyoluteorin biosynthesis genes and pyoluteorin production in Pf-5. This report provides evidence of a coordination of pyoluteorin production and the transcription of genes encoding a linked transport apparatus, wherein each requires the other for optimal expression.