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David R. Nelson

Host-pathogen interactions in Vibrio anguillarum

This bacterium causes vibriosis, a hemorrhagic septicemia, in a wide variety of fish, shellfish, and crustaceans. We are interested in identifying, cloning, and characterizing V. anguillarum genes expressed during colonization of the fish gastrointestinal tract. We have previously identified several V. anguillarum proteins expressed during growth in fish intestinal mucus. We have also characterized the starvation-stress response of this pathogen. Our current focus is on the regulation of expression of the extracellular metalloprotease (encoded by empA) and the hemolysin (encoded by vah1). We have demonstrated that empA expression is induced by incubation in fish gastrointestinal mucus when the cells are at high density. We have shown that the expression of empA is dependent upon the alternative sigma factor, RpoS. We have also demonstrated that expression of the EmpA protein requires post-translational processing. Recent work has determined that vah1 expression is regulated by a gene that encodes a phospholipase homologue. Additionally, it appears that there are two separate hemolysin operons. Aspects of this work are done in collaboration with Dr. Marta Gomez-Chiarri (URI) and Dr. Terrence Bradley (URI).

Vibrio anguillarum stained with uranyl acetate. Cells were grown overnight in LB20 at 27°C. Note the single polar flagellum. Electron micrograph by Paul Johnson (URI Genomics and Sequencing Center).

Selected publications:

• Garcia, T., K. Otto, S. Kjelleberg, and D.R. Nelson. 1997. The growth of Vibrio anguillarum in salmon intestinal mucus. Appl. Environ. Microbiol. 63:1034-1039.
• Nelson, D.R., Y. Sadlowski, M. Eguchi, K. Otto, and S. Kjelleberg. 1997. The starvation-stress response of Vibrio anguillarum. Microbiology 143:2305-2312.
• Denkin, S. M. and D. R. Nelson. 1999. Induction of protease activity by gastrointestinal mucus in Vibrio anguillarum. Appl. Environ. Microbiol. 65:3555-3560.
• Soffientino, B., T. Gwaltney, D. R. Nelson , J.L. Specker, M. Mauel, and M. Gomez-Chiarri. 1999. Infectious nectrotizing enteritis and mortality caused by Vibrio carchariae in summer flounder (Paralichthys dentatus) during intensive culture. Dis. Aquat. Organ. 38:201-210.
• Denkin, S.M. and D.R. Nelson. 2004. Regulation of Vibrio anguillarum empA Metalloprotease Expression and Its Role in Virulence. Appl. Environ. Microbiol. 70:4193-4204
• Starocik, A.M., S.M. Denkin, and D.R. Nelson. 2005. Regulation of the Vibrio anguillarum metalloprotease EmpA by post-translational modification. J. Bacteriol. 187:2257-2260