Quorum-sensing-dependent regulation of biosynthesis of the polyketide antibiotic mupirocin in Pseudomonas fluorescens NCIMB 10586

Mupirocin (pseudomonic acid) is a polyketide antibiotic, targeting isoleucy l-tRNA synthase, and produced by Pseudomonas fluorescens NCIMB 10586. It is used clinically as a topical treatment for staphylococcal infections, part icularly in contexts where there is a problem with methicillin-resistant St aphylococcus aureus (MRSA). In studying the mupirocin biosynthetic cluster the authors identified two putative regulatory genes, mupR and mupI, whose predicted amino acid sequences showed significant identity to proteins invo lved in quorum-sensing-dependent regulatory systems such as LasR/LuxR (tran scriptional activators) and LasI/LuxI (synthases for N-acythomoserine lacto nes - AHLs - that activate LasR/LuxR). Inactivation by deletion mutations u sing a suicide vector strategy confirmed the requirement for both genes in mupirocin biosynthesis. Cross-feeding experiments between bacterial strains as well as solvent extraction showed that, as predicted, wild-type P. fluo rescens NCIMB 10586 produces a diffusible substance that overcomes the defe ct of a mupI mutant. Use of biosensor strains showed that the MupI product can activate the Pseudomonas aeruginosa lasRIasI system and that P. aerugin osa produces one or more compounds that can replace the MupI product. Inser tion of a xyIE reporter gene into mupA, the first ORF of the mupirocin bios ynthetic operon, showed that together mupR/mupI control expression of the o peron in such a way that the cluster is switched on late in exponential pha se and in stationary phase.