Cloning and Characterization ofvuuA, a Gene Encoding theVibrio vulnificusFerric Vulnibactin Receptor

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Abstract
The ability ofVibrio vulnificusto acquire iron from the host has been shown to correlate with virulence. Many iron transport genes are regulated by iron, and inV. vulnificus, transcriptional regulation by iron depends on thefurgene. The N-terminal amino acid sequence of a 72-kDa iron-regulated outer membrane protein purified from aV. vulnificus furmutant had 53% homology with the first 15 amino acids of the mature protein of theVibrio choleraevibriobactin receptor, ViuA. In this report, we describe the cloning, DNA sequence, mutagenesis, and analysis of transcriptional regulation of the structural gene for VuuA, the vulnibactin receptor ofV. vulnificus. Analysis of the DNA sequence of thevuuApromoter region demonstrated a sequence identical to the upstream Fur box ofV. cholerae viuA. Northern blot analysis showed that the transcript was strongly regulated by iron. The amino acid sequence of VuuA was 74% identical to the sequence ofV. choleraeViuA and was homologous to those of several TonB-dependent outer membrane receptors. An internal deletion of theV. vulnificus vuuAgene resulted in the loss of expression of the 72-kDa protein and the loss of the ability to use transferrin or vulnibactin as a source of iron. This mutant showed reduced virulence in an infant mouse model. Introduction of a plasmid containing the completeviuAcoding sequence and 342 bp of upstream DNA into the mutant restored ferric vulnibactin and ferric transferrin utilization to the mutant.

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