Genetic analysis of the Erwinia chrysanthemi 3937 chrysobactin iron-transport system: characterization of a gene cluster involved in uptake and biosynthetic pathways

Twenty of the twenty-two MudII1734 insertions impairing the chrysobactin iron-assimilation system of Erwinia chrysanthemi 3937 were localized to a 50 kbp genomic insert contained in the R-prime plasmid, R'4 (Enard et al., 1988). Using the conjugative plasmid pULB110 (RP4::mini-Mu) and the generalized transducing phage phi EC2, we located this iron-transport region and the two unlinked mutations on the chromosome linkage map. Chrysobactin is a catechol-type siderophore and, as we have previously observed with the entA locus of Escherichia coli, the E. chrysanthemi-derived R'4 was found to complement E. coli entB and entE mutations. A 2.9 kb EcoRi and a 4.8 kb BamHI fragment in the R'4 sharing homology with the E. coli entCEBAP15 operon DNA were subcloned. These fragments were used as DNA/DNA hybridization probes to screen a wild-type gene library, yielding a recombinant cosmid (pEC7) able to complement mutations disrupting the 2,3-dihydroxybenzoic acid biosynthetic pathway in both Erwinia and Escherichia spp. as well as the E. coli entE mutation. Physical mapping of the genomic MudII1734 insertions corresponding to these mutations led to the identification of a cluster of genes confined to a DNA sequence of about 10 kb required for both biosynthetic and receptor functions.