The pyrH gene of Vibrio vulnificus is an essential in vivo survival factor.

We have suggested an important role of the pyrH gene during the infectious process of Vibrio vulnificus. Previously, we have identified 12 genes expressed preferentially during human infections by using in vivo-induced antigen technology. Among the in vivo-expressed genes, pyrH encodes UMP kinase catalyzing UMP phosphorylation. Introduction of a deletion mutation to the pyrH gene was lethal to V. vulnificus, and an insertional mutant showed a high frequency of curing. We constructed a site-directed mutant strain (R62H/D77N) on Arg-62 and Asp-77, both predicted to be involved in UMP binding, and characterized the R62H/D77N strain compared with the previously reported insertional mutant. We further investigated the essential role of the pyrH gene in the establishment of infection using the R62H/D77N strain. Cytotoxicity was decreased in the R62H/D77N strain, and the defect was restored by an in trans complementation. The intraperitoneal 50% lethal dose of the R62H/D77N strain increased by 26- and 238,000-fold in normal and iron-overloaded mice, respectively. The growth of the R62H/D77N strain in 50% HeLa cell lysate, 100% human ascitic fluid, and 50% human serum was significantly retarded compared to that of the isogenic wild-type strain. The R62H/D77N mutant also had a critical defect in the ability to survive and replicate even in iron-overloaded mice. These results demonstrate that pyrH is essential for the in vivo survival and growth of V. vulnificus and should be an attractive new target for the development of antibacterial drugs and replication-controllable live attenuated vaccines.