Involvement of enterobactin synthesis pathway in production of Microcin H47

Microcin H47 (MccH47) is a gene-encoded peptide antibiotic produced by an Escherichia coli clinical isolate which is active on strains of gram-negative bacteria. Its uptake by E. coli K-12-susceptible cells depends on the presence of any of the outer membrane proteins Cir, Fin, and FepA, the three catechol receptors of this organism. The nucleotide sequence of a portion of the MccH47 genetic system that had not yet been studied was elucidated. Five open reading frames were identified, three of which corresponded to genes encoding functions related to catechol-type siderophores: mchA and mchS1 are iroB and iroD homologues, respectively, and mchS4 was found to promote the production of the catecholate siderophore enterobactin. The possible relationship between enterobactin synthesis and MccH47 production was studied. Enterobactin-deficient strains failed to produce MccH47 when transformed with the antibiotic genetic determinants and upon introduction of the ent genetic cluster, the production of both the siderophore and MccH47 was restored. Further studies demonstrated that at least the enterobactin nonribosomal peptide synthase EntF is necessary for MccH47 synthesis. The relationship found between MccH47 and catecholate siderophore production is discussed, and a model outlining MccH47 synthesis is proposed.