A LOCUS CODING FOR PUTATIVE NON RIBOSOMAL PEPTIDE POLYKETIDE SYNTHASEFUNCTIONS IS MUTATED IN A SWARMING-DEFECTIVE PROTONS MIRABILIS STRAIN/

We describe a large bacterial locus that, unusually, encodes component s typically required for both the non-ribosomal synthesis of peptides and also polyketide/fatty acid synthase function. Two tandem ABC trans porter genes in this putative nrp (non-ribosomal peptide/polyketide) o peron suggest that the principal product may be secreted. Immediately distal to the nrp operon is a gene, irpP, encoding a small peptide sim ilar to the Bacillus ComX pheromone that in its mature, extracellular form increases expression of unlinked non-ribosomal peptide synthesis genes. Transcription of both the nrp operon and irpP was up-regulated in iron-limiting culture conditions, consistent with the presence of a putative Fur repressor-binding site 5' of irpP. The locus was isolate d from Proteus mirabilis as the site of a TnphoA insertion causing imp aired swarm cell differentiation and an aberrant swarming pattern. The mutation was in one of the transporter genes, but a comparable swarmi ng defect resulted from interposon disruption of the putative nrp synt hetase gene.