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Abstracts
Workgroup: Frontiers in Disease Research
Comparative Pathogenesis of P. marinus Disease in Bivalves: Development of Prevention Strategies for C. virginica.
Principal Investigator(s):
Robert S. Anderson, Ph.D., University of Mayland Center for Environmental Science, Cheasapeake Bay Lab, anderson@cbl.umces.edu
Funding Period: 9/1/97-8/31/99
The antimicrobial activity of sera from bivalves with different resistance to dermo disease (Crassostrea virginica, C. gigas, Mytilus edulis, and Geukensia demissa) was tested from antimicrobial activity. Test microorganisms included a laboratory-propagated P. marinus strain and a bacterium, Bacillus megaterium. The growth kinetics of P. marinus in the presence of bivalve sera were measured turbidometrically. Bactericidal activity was quantified by determining the percent survivorship after serum exposure by the MTS/PMS assay. Activity was compared after calculating EC50 values (ug serum protein concentration required to inhibit/kill 50% of the test microbes). Serum from Maine (dermo-free) and local (dermo-exposed) C. virginica had comparable, low levels of anti-P. marinus activity, suggesting that parasite exposure was not the sole determinant of activity. Serum from C. gigas had no anti-P. marinus activity, although this species is reportedly resistant to dermo. Both mussel species tested had many hundred-fold higher anti-P. marinus activity than C. virginica. Anti-B. megaterium activity was consistently recorded for both oyster species, as well as for M. edulis. Antibacterial activity was not seen in G. demissa serum. Hemocyte extracts from all bivalves tested showed higher specific activity than did the corresponding serum samples. Ultrafiltration of bivalve sera showed that, in addition to antimicrobial proteins, M. edulis has active <10 kDa anti-P. marinus peptides that resemble defensins. These active peptides were more difficult to demonstrate in G. demissa and the oysters.
IMPACTS and/or BENEFITS:
These data indicate that antimicrobial agents show species-specific patterns of expression by bivalves, are produced and secreted by hemocytes, and may partially determine resistance to infectious disease. Some of the main conclusions of this study include: a) Although C. virginica and C. gigas differ in resistance to P. marinus, their sera contains comparable, very low levels of anti-P. marinus activity. b) In C. virginica, P. marinus exposure/infection does not influence their low level of anti-P. marinus activity. c) Although oysters have low serum anti-P. marinus activity, their serum contains strong antibacterial (anti-B. megaterium) activity. d) Mussels have serum proteins with 100- to 600-fold greater anti-P. marinus activity than oysters, probably a basis for their dermo resistance. e) Hemocytes secrete antimicrobial molecules in all bivalve species examined. f) Anti-P. marinus activity of M. edulis is mediated by a <10 kDa defensin-like molecule.
PROJECT PUBLICATIONS:
Anderson, R. S. and A. E. Beaven. 2000. Antimicrobial activity in cell-free hemolymph of oysters and mussels. J. Shellfish Res. 19: 641.
Anderson, R. S. and A. E. Beaven. 2001. Antibacterial activities of oyster (Crassostrea virginica) and mussel (Mytilus edulis and Geukensia demissa) plasma. Aquat. Living Resour. 14: 343-349.
Anderson, R. S. and A. E. Beaven. 2001. A comparative study of anti-Perkinsus marinus activity in bivalve sera. J. Shellfish Res. 20: 1011-1017.
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