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Regulation of the antibiotic pyoluteorin in Pseudomonas fluorescens Pf-5 includes positive autoregulation, and influence by 2,4-diacetylphloroglucinol and pyrrolnitrin

Regulation of the antibiotic pyoluteorin in Pseudomonas fluorescens Pf-5 includes positive autoregulation, and influence by 2,4-diacetylphloroglucinol and pyrrolnitrin

Abstracts of the General Meeting of the American Society for Microbiology 103: K-107

Background: The focus of this study is the regulation of an antibiotic, pyoluteorin (PLT), produced by the plant-associated soil bacterium Pseudomonas fluorescens Pf-5. PLT, a chlorinated polyketide, is one of a suite of antibiotics produced by Pf-5 that antagonize seed- and root-rotting plant pathogens. We recently found that regulation of PLT production in Pf-5 includes autoinduction; moreover, additions of two other antibiotics, 2,4-diacetylphloroglucinol (PHL) and pyrrolnitrin, impacted the level of PLT biosynthetic gene transcription. Methods and Results: Using HPLC and transcriptional fusions, we found that, in Pf-5, PLT and PHL (both polyketide antibiotics secreted by Pf-5) each positively regulated their own production while mutually inhibiting one another's production. This phenomenon occurred i) in the presence of low (nanomolar) concentrations of either compound, and ii) at the transcriptional level, for PLT. Moreover, PLT autoinduction occurred in vivo, as demonstrated by cross-feeding experiments on seeds and roots in pasteurized soil. The existence of the PLT signaling phenomenon raises the question of a PLT receptor. A cluster of ten genes has been shown to be required for PLT biosynthesis, and transcription of genes within the cluster requires the linked gene pltR, which encodes a member of the LysR family of transcriptional regulators. Members of the LysR family typically exert pathway-specific, cofactor-dependent control over linked loci. The cofactor often is the very compound whose production is under regulation. Because both PLT gene transcription and autoinduction are absent in a pltR mutant, we are currently pursuing the hypothesis that PLT signaling is mediated by the binding of PLT to the PltR protein, inducing PltR to activate transcription from promoters within the PLT biosynthetic gene cluster. Conclusion: Our experiments suggest i) that regulation of PLT production may involve crosstalk among antibiotics of Pf-5, and ii) that a new role for PLT as an intra- and intercellular signaling compound exists, in addition to its previously known role as a toxin.

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