Identification of an operon required for ferrichrome iron utilization in Vibrio cholerae

Mutagenesis of Vibrio cholerae with TnphoA, followed by screening for fusio ns that were activated under low-iron conditions, led to the identification of seven independent fusion strains, each of which was deficient in the ab ility to utilize ferrichrome as a sole iron source for growth in a plate bi oassay and had an insertion in genes encoding products homologous to Escher ichia coli FhuA or FhuD. Expression of the gene fusions was independent of IrgB but regulated by Fur. We report here a map of the operon and the predi cted amino acid sequence of FhuA, based on the nucleotide sequence. Unlike those of the E. coli fhu operon, the V. cholerac ferrichrome utilization ge nes are located adjacent and opposite in orientation to a gene encoding an ATP-binding cassette transporter homolog, but this gene, if disrupted, does not affect the utilization of ferrichrome in vitro.