• Ph.D. (1979) University of California, Los Angeles
• M.S. (1974) University of Wisconsin, Madison
• A.B. (1972) University of California, Los Angeles
• Post-doctoral fellow (1979-1982) University of California, Berkeley

• MIC413 - Advanced Microbiology Lecture I
• MIC415 - Advanced Microbiology Laboratory I
• MIC414 - Advanced Microbiology Lecture II
• MIC416 - Advanced Microbiology Laboratory II
• MIC561 - Recent Advances in Molecular Cloning

Physiology and gene expression in Borrelia burgdorferi

We are investigating the physiology of B. burgdorferi (the causative agent of Lyme disease) with an emphasis on gene expression during starvation-stress. Lyme disease is the most prevalent arthropod vector-borne disease in North America. B. burgdorferi cells shuttle between their tick-vector and their mammalian hosts. The tick host (Ixodes scapularis) takes only three blood meals during its two-year life cycle, yet the bacteria survive for extended periods in the tick midgut between feedings. Additionally, the bacteria may enter nutrient limited sites in the mammalian host, such as the cerebral spinal fluid. We are interested in examining the regulation of the of gene expression during starvation or nutrient limitation. Recent evidence from my lab suggests that B. burgdorferi cells: 1) respond to serum starvation with a temporally controlled program of changes in protein expression; and 2) regulate their responses to starvation by the stringent response, controlled by SpoT (encoded by spoT) and by alternative sigma factors such as RpoS or sigma squared(encoded by rpoS). This work is being carried out in collaboration with Dr. Thomas Mather (URI), Dr. Ira Schwartz (NY Medical College), and Dr. Richard Marconi (Virginia Commonwealth University). Our previous studies of B. burgdorferi have examined heat shock or stress-proteins and their roles in disease and as chaperone proteins.

Host-pathogen interactions in Vibrio anguillarum

Vibrio anguillarum is the causative agent of warm water vibriosis, a hemorrhagic septicemia, in a wide variety of fish, shellfish, and crustaceans. Infections by this organism are a major impediment to marine aquaculture and result in large economic losses to that industry. We are investigating the molecular basis of virulence in this bacterial pathogen. We are currently investigating two virulence factors in this bacterium – extracellular protease activity and hemolytic activity. We have shown that the major extracellular protease, EmpA (encoded by the empA gene) is synthesized as a pre-pro-protein, secreted by the type 2 secretion system as pro-EmpA, and subsequently processed extracellularly to the mature EmpA by a second secreted protease, Epp. We are interested in determining the roles of EmpA, pro-EmpA, and Epp in promoting pathogenesis. We have also characterized the hemolytic activity of V. anguillarum and have discovered that there are two gene clusters that encode at least 8 genes that define the hemolytic activity. One gene cluster includes vah1 and plp. The Vah1 protein acts as a hemolysin/cytotoxin, while the Plp protein has phospholipase A2 activity. The second gene cluster contains 6 genes, rtxACHBDE. The RtxA protein (~440kDa) is a powerful hemolysin/cytotoxin that is a member of the multi-functional autoprocessing repeat-in-toxin (MARTX) toxin family. The rtxBDE genes encode the type 1 secretion system necessary for the secretion of RtxA. We are currently investigating the regulation of gene expression of the hemolysins and also the mechanisms by which they act as cytotoxins and hemolysins.

Oriol Sunyer, PhD (Univ. Penn.)

1. Li, L., X. Mo, and D.R. Nelson. 2011. HlyU is a positive regulator of hemolysin expression in Vibrio anguillarum. J. Bacteriol. 193:4779-4789.

2. Rhodes, R.G., J.A. Atoyan, and D.R. Nelson. 2010. The chitobiose transporter, chbC, is required for chitin utilization in Borrelia burgdorferi. BMC Microbiology 10:21.

3. Rhodes, R.G., W. Coy, and D.R. Nelson. 2009. Chitobiose utilization in Borrelia burgdorferi is dually regulated by RpoD and RpoS. BMC Microbiology 9:108.

4. Staroscik, A.M. and D.R. Nelson. 2008. The influence of salmon surface mucus on the growth of Flavobacterium columnare. J. Fish Dis. 31:59-69.

5. Fallon, B.A., J.G. Keilp, K.M. Corbera, E. Petkova, C.B. Britton, E. Dwyer, I. Slavov, J. Cheng, J. Dobkin, D.R. Nelson, H.A. Sackeim. 2008. A randomized, placebo-controlled trial of repeated IV antibiotic therapy for Lyme encephalopathy. Neurology 70:992-1003.

6. Varina, M., S.M. Denkin, A.M. Staroscik, and D.R. Nelson. 2008. Identification and characterization of Epp, the secreted processing protease for the Vibrio anguillarum EmpA metalloprotease. J. Bacteriol. 190:6589-6597.

7. Li, L., J.L. Rock, and D.R. Nelson. 2008. Identification and characterization of an RTX gene cluster in Vibrio anguillarum. Infect. Immun. 76:2620-2632.

8. Rock, J.L. and D.R. Nelson. 2006. Identification and characterization of a hemolysin gene cluster in Vibrio anguillarum. Infect. Immun. 74:2777-2786.

9. 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.

10. 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.

11. Denkin, S.M., P. Sekaric, and D.R. Nelson. 2004. Gel shift analysis of the empA promoter region in Vibrio anguillarum. BMC Microbiology 4:42.

12. Concepcion, M.B. and D.R. Nelson. 2003. Expression of spoT in Borrelia burgdorferi during serum starvation. J. Bacteriol. 185:444-452.

13. Roberts, D.M., M.J. Caimano, J.D. Radolf, D.R. Nelson, and R.T. Marconi. 2002. Influence of environmental conditions on the expression and cellular partitioning of members of the Bdr protein family in the Lyme disease spirochetes. Infect. Immun. 70:7033-7041.

14. Nelson, D.R., Rooney, S., N. Miller, and T.N. Mather. 2000. Complement-mediated killing of Borrelia burgdorferi in deer sera. J. Parasitol. 86:1232-1238.

15. Alban, P.S., P.W. Johnson, and D.R. Nelson. 2000. Serum starvation-induced changes in protein synthesis and morphology of Borrelia burgdorferi. Microbiology 146:119-127.

16. Denkin, S. M. and D. R. Nelson. 1999. Induction of protease activity by gastrointestinal mucus in Vibrio anguillarum. Appl. Environ. Microbiol. 65:3555-3560.

17. 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.

18. Nelson, D.R., Y. Sadlowski, M. Eguchi, K. Otto, and S. Kjelleberg. 1997. The starvation-stress response of Vibrio anguillarum. Microbiology 143:2305-2312.

19. 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.

20. Ewing, C.A. Scorpio, D.R. Nelson, and T. Mather. 1994. Isolation of Borrelia burgdorferi from saliva of the tick vector, Ixodes scapularis. J. Clin. Microbiol. 32:755-758.

21. Scorpio, A., A. Laquerre, P. Johnson, D.C. Laux, and D.R. Nelson. 1994. Subcellular localization and chaperone functions of Hsp60 and Hsp70 in Borrelia burgdorferi. J. Bacteriol. 176:6449-6456.

22. Girouard, L.A., S. Jindal, D.C. Laux, and D.R. Nelson. 1993. Immune recognition of human Hsp60 by Lyme disease patient sera. Microbial Path. 14:287-297.