CLONING OF A VIBRIO-CHOLERAE VIBRIOBACTIN GENE-CLUSTER - IDENTIFICATION OF GENES REQUIRED FOR EARLY STEPS IN SIDEROPHORE BIOSYNTHESIS

Vibrio cholerae secretes the catechol siderophore vibriobactin in resp onse to iron limitation. Vibriobactin is structurally similar to enter obactin, the siderophore produced by Escherichia coli, and both organi sms produce 2,3-dihydroxybenzoic acid (DHBA) as an intermediate in sid erophore biosynthesis. To isolate and characterize V. cholerae genes i nvolved in vibriobactin biosynthesis, we constructed a genomic cosmid bank of V. cholerae DNA and isolated clones that complemented mutation s in E. coli enterobactin biosynthesis genes. V. cholerae homologs of entA, entB, entC, entD, and entE were identified on overlapping cosmid clones. Our data indicate that the vibriobactin genes are clustered, like the E. coli enterobactin genes, but the organization of the genes within these clusters is different. In this paper, we present the org anization and sequences of genes involved in the synthesis and activat ion of DHBA. In addition, a V. cholerae strain with a chromosomal muta tion in vibA was constructed by marker exchange. This strain was unabl e to produce vibriobactin or DHBA, confirming that in V. cholerae VibA catalyzes an early step in vibriobactin biosynthesis.