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E. Fidelma Boyd, Ph.D.
BISC 682 Molecular Mechanisms of Pathogens
BISC 850 Advanced Topics in Microbiology
Vibrio parahaemolyticus an emerging human pathogen
Vibrio parahaemolyticus is the leading cause of bacterial seafood borne gastroenteritis worldwide. In recent years, a novel pandemic O3:K6 serogroup hypervirulence strain has emerged. This new variant contains several genomic regions known as pathogenicity islands that are absent from non pathogenic strains (Hurley et al., 2006, Boyd et al., 2008). One of our questions is to determine the factors that aided the emergence of the pandemic clone. To this end, we developed a new in vivo adult mouse model for V. parahaemolyticus colonization. Our new mouse model allows us for the first time to determine the bacterial factors required for host colonization. We have identified a number of global gene regulators important for in vivo survival (Whitaker et al., 2012, 2014, Haines-Menges et al, in preparation). For example, the Vibrio specifc ToxRS regulator is important for colonization through its regulation of the porin OmpU (Whitaker et al., 2012). The data suggest that there are discordant roles for sigma factors RpoS, RpoE and RpoN in colonization of the mouse intestine (Whitaker, et al., 2013; Haines-Menges et al, in preparation). An rpoN deletion mutant strain is a superior colonizer compared to the wild-type strain and this phenotype is due in part to a faster growth rate on intestinal mucus as well as individual components of mucus (Whitaker, et al., 2014). We have also identified a V. parahaemolyticus natural isolate that is a more proficient colonizer that either our wild-type or rpoN mutant strains. One of our questions is to determine the carbon utlization patterns in vivo and the different fitness effects of different carbon and nitrogen sources.
Vibrio parahaemolyticus is a halophile that is present in all coastal waters around the world. Salinity is an absolute requirement for growth and the bacterium can grow in up to 10% NaCl. Why and how this species is adapted to high salt tolerance whereas sister species have not is unknown. We identified in the genome unique clusterings of genes that show homology to osmotolerance systems (Boyd et al., 2008; Naughton et al., 2009). Comparative physiological analysis determined that under a number of different stress conditions, V. parahaemolyticus had a growth advantage compared to other Vibrio species (Naughton et al., 2009). Our data show that growth at moderate and high salinity compared to low salinity protects at low pH (Whitaker et al., 2010; Kalburge et al., 2013). We demonstrated that only the ectoine synthesis system but not the glycine betaine synthesis system is essential for fitness and survival at high salinity under low nutrient conditions (Ongagna-Yhombi and Boyd, 2013). Using in vitro competition assays we are examininig the fitness effects of different compatible solute transporter deletion mutation on survival (Ongagna-Yhombi and Boyd., unpublished data).
Vibrio cholerae, the causative agent of the dreaded diarrheal disease cholera
Two virulence factors are indispensable for infection, cholera toxin and the toxin corregulated pilus, and both are encoded on mobile and integrative gentic elements (MIGEs); the filamentous phage CTXphi and the TCP island or Vibrio Pathogenicity Island (VPI), respectively. My group identified a second pathogenicity island named VPI-2, which is present among all pathogenic isolates (Jermyn and Boyd, 2002, 2005). VPI-2 encodes the genes required for sialic acid scavenaging (nanH), uptake (siaPQM) and catabolism (nanA, nanEK, nagA) (Jermyn and Boyd, 2002, 2005, Almagro-Moreno and Boyd, 2009a). Sialidase encoded by nanH cleaves terminal sialic acid, a nine carbon backbone monosaccharide present on all cell surfaces, from cell surface glycans. In the intestinal mucin, sialidase converts host sialoglycans to GM1 gangliosides, the cell receptors for CT, with the release of free sialic acid that can be taken up and catabolized as a sole carbon and nitrogen source by V. cholerae (Almagro-Moreno and Boyd, 2009a). We demonstrated that the TRAP transporter SiaPQM (VC1777-VC1779) is the sole sialic acid transporter present in V. cholerae (Chowdhury et al., 2012). One of our research goals is to demonstrate that host specific glycans are essential for V. cholerae growth and survival in vivo.
Pathogenicity islands are large chromosomal regions acquired by a pathogenic strains within a species. We are examining the mechanisms of excision and integration of VPI-1 and VPI-2 and the role of island-encoded and host-encoded factors play in these functions. We demonstrated that VPI-2 can excise from the genome and a form circular intermediate and this is catalyzed by an integrase and excisionase encoded within VPI-2 (Murphy and Boyd, 2008; Almagro-Moreno et al., 2010). Our data suggests that there is cross talk between different islands in V. cholerae and this communication is mediated by RDFs/excisionases (Carpenter and Boyd, unpublshed data).
Vibrio vulnificus a marine bacterium and opportunistic pathogen of humans
Vibrio vulnificus is a highly invasive pathogen of both fish and humans.V. vulnificus population genetic structure consists of at least two major lineages containing unique regions required for survival within its varied niches (Cohen et al., 2007). We are using molecular genetic and genomic approaches to determine the key elements that allow the organism to survive in molluscs, fish and humans. We have identified in the genome a large number of regions unique to each sequenced strain (Quirke et al., 2006). One such region is region XII, a 33 kb cluster that encodes genes for the transport and metabolism of glycoaminoglycans (GAGs). GAGs can potentially be used by the bacterium as a carbon and nitrogen source and may explain the highly invasive nature of this species.
V. vulnificus can both catabolize and synthesize sialic acid. Only clinical isolates can catabolize sialic acid and these isolates encode a single transporter for sialic acid uptake similar to that found in V. cholerae (Lubin et al, 2012). All isolates appear to be capable of sialic acid biosynthesis. The two sequenced strains of V. vulnificus encode highly divergent sialic acid biosynthesis neu/nab genes and we have shown that the two strains produce different amounts of sialic acid (Lewis et al., 2011). Also it appears that V. vulnificus can synthesize different types of sialic acid (Lewis et al., 2011). We are investigating the type of sialic acid produced by V. vulnificus and the surface structure(s) that is decorated with this compound (Lubin et al. 2014 in preparation).
Megan R. Carpenter, B.S., -Ph.D./M.B.A. Graduate student program, (B.S. Lafayette College, PA), Vibrio pathogenicity Island excision and integration in Vibrio cholerae
Brandy Haines-Menges, B.S., -Ph.D. Graduate student in Chemistry Biology Interface Program, (B.S. Cedar Crest College, PA), Vibrio parahaemolyticus sigma factor regulatory systems
Sai Siddarth Kalburge, B.S. -Ph.D/M.B.A. Graduate student program, (B.S. Viswesvaraya Technological University, India), Vibrio parahaemolyticus stress responses.
Jean-Bernard Lubin B.S., -Ph.D. Graduate student in Chemistry Biology Interface Program, (B.S. Farmingdale State College, NY). Vibrio vulnificus sialic acid biosynthesis and catabolism
Nathan McDonald, B.S., Ph.D. Graduate student in Chemistry Biology Interface Program, (B.S. University of Delaware). Vibrio physiology and metabolism
Serge Ongagna-Yhombi, M.S., -Ph.D. Graduate student, (B.S. Marien Ngouabi University Brazzaville, Congo) Vibrio parahaemolyticus osmotic tolerance mechanisms
Abish Regmi, B.S., M.S. Graduate student (B.S. Towson State University). Vibrio vulnificus ecology and evolution.
Laura Powell, Undergraduate Researcher, University of Delaware
Molly Peters, Undergraduate Researcher, University of Delaware
1. Chowdhury, N. and E.F. Boyd. 2014. Identification and characterization of aerobic C4-dicarboxylate transporters in the human pathogen Vibrio cholerae. In Preparation.
2. Lubin, J.B., W.G. Lewis, N.M Gilbert, S. Almagro-Moreno, E.F. Boyd, and A.L. Lewis. 2014. Sialic acid-like molecules expressed on Vibrio vulnificus lipopolysaccharide are essential for bloodstream survival in a murine model of septicemia. In preparation.
3. Ongagna-Yhombi, S.Y. and E.F. Boyd. 2014. Deciphering the role of betaine choline carnitine transporters in the halophile Vibrio parahaemolyticus. Submitted.
4. Haines-Menges, B.L., Whitaker, W.B., and E.F. Boyd. 2014. The alternative sigma factor RpoE is essential for Vibrio parahaemolyticus cell envelope stress response and intestinal colonization. Submitted.
5. Haines-Menges, B.L., Whitaker, W.B., J.B. Lubin, and E.F. Boyd. 2014. Host Sialic Acids: A delicacy for the pathogen with discerning taste. In Metabolism and Bacterial Virulence. Edited T. Conway and P. Cohen, ASM Press. In Press.
6. Chowdhury, N., J.J. Kingston, W.B. Whitaker, M.R. Carpenter, A.L. Cohen, and E.F. Boyd. 2014. Sequence and expression divergence in an ancient gene duplication of the chaperonins groELgroES in Vibrio species. Submitted.
7. Kalburge, S.S., S. Polson, K. Boyd Crotty, L. Katz, M. Turnsek, C.L. Tarr, J. Martinez-Urtaza, and E.F. Boyd. 2014. Complete genome sequence of Vibrio parahaemolyticus UCM V493. Genome Announcements, 13;2(2).
8. Kalburge, S.S., Whitaker, W.B., and E.F. Boyd. 2014. High salt pre-adaptation of Vibrio parahaemolyticus enhances survival to lethal environmental stresses. J. Food Protection, 77(2):246-53.
9. Richards, G.P, M.A. Watson, E.F. Boyd, W. Burkhardt III, R. Lau, J. Uknalis and J. Fay. 2014. Seasonal levels of the Vibrio predator Bacteriovorax in Atlantic, Pacific and Gulf Coast Seawater. International Journal of Microbiology, In Press.
10. Whitaker, W.B., G.P. Richards, and E.F. Boyd. 2014. Loss of the sigma factor RpoN increases intestinal colonization proficiency of Vibrio parahaemolyticus in an adult mouse model. Infection and Immunity, 82:544-556.
Phone: (302) 831-1088
Fax: (302) 831-2281
Office: 328 Wolf Hall
Lab: 353 Wolf Hall
Department of Biological Sciences
University of Delaware
Newark, DE 19716
- B.S., Ph.D. - National University of Ireland (Galway, Ireland)
- Postdoctoral - The Pennsylvania State University
- Postdoctoral - Harvard University
- Postdoctoral - Tufts University School of Medicine