Cloning and characterization of vuuA, a gene encoding the Vibrio vulnificus ferric vulnibactin receptor

The ability of Vibrio vulnificus to acquire iron from the host has been sho wn to correlate with virulence. Many iron transport genes are regulated by iron, and in V. vulnificus, transcriptional regulation by iron depends on t he fur gene. The N-terminal amino acid sequence of a 72-kDa iron-regulated outer membrane protein purified from a V, vulnificus fur mutant had 53% hom ology with the first 15 amino acids of the mature protein of the Vibrio cho lerae vibriobactin receptor, ViuA, In this report, we describe the cloning, DNA sequence, mutagenesis, and analysis of transcriptional regulation of t he structural gene for VuuA, the vulnibactin receptor of V. vulnificus. Ana lysis of the DNA sequence of the vuuA promoter region demonstrated a sequen ce identical to the upstream Bur box of V, cholerae viuA. Northern blot ana lysis showed that the transcript was strongly regulated by iron. The amino acid sequence of VuuA was 74% identical to the sequence of V. cholerae ViuA and was homologous to those of several TonB-dependent. outer membrane rece ptors, An internal deletion of the V.: vulnificus vuuA gene resulted in the loss of expression of the 72-kDa protein and the loss of the ability to us e transferrin or vulnibactin as a source of iron. This mutant showed reduce d virulence in an infant mouse model. Introduction of a plasmid containing the complete viuA coding sequence and 342 bp of upstream DNA into the mutan t restored ferric vulnibactin and ferric transferrin utilization to the mut ant.