Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Stephen L. Kaattari


Perkinsus marinus is an alveolate protozoan parasite of the eastern oyster (Crassostrea virginica) which is responsible for much of the decline in United States oyster populations. Perkinsus marinus can be cultured in vitro, but is rapidly attenuated in the process. Supplementation of a protein-free medium with oyster products altered proliferation, changed protease expression in the parasite extracellular products (ECP), induced morphological forms typically seen in vivo, and partially reversed parasite attenuation. Supplements derived from dissected oyster tissues were used to determine if these changes could be differentially elicited. These supplements, with the exception of adductor muscle, reduced proliferation. Whole oyster and digestive gland/gonad supplements favored palintomic, rather than binary, fission. The total ECP protease activity was generally decreased in supplemented cultures, though gill/mantle supplements may have induced proteases. A low molecular weight subset of proteases was upregulated most effectively by heart- and adductor muscle-derived supplements. Serine proteases and other ECP proteins may be virulence factors. Attempts to create antibodies to study P. marinus cells and ECP have been largely unsuccessful due to poor immune responses and crossreactivity. Ultrafiltration-concentrated P. marinus ECP were poorly immunogenic and toxic to experimental animals. Immunogenicity was not substantially affected by heat denaturation or proteolytic inhibition. Co-administration of ECP with oyster plasma caused a suppression in the anti-plasma antibody response with restriction of epitope recognition. Analysis of medium constituents revealed that a surfactant, Pluronic F-68 (PF68), was immunosuppressive. Although isolated protein antigens from the ECP remained immunosuppressive, separation of the antigens from PF68 enabled antibody production. Five monoclonal antibodies were created against ECP from unsupplemented medium and were used to study ECP function, regulation, and mechanism of storage and release. ECP are secreted by release from the cell wall and from two morphologically distinct intracellular compartments. A sandwich ELISA allowed quantification of an ECP protein with significantly reduced expression in supplemented cultures. Another antibody, which specifically bound to trophozoite and tomont walls, was used to investigate morphological and antigenic changes during thioglycollate-induced formation of prezoosporangia, and confirm supplement-induced formation of prezoosporangia. This antibody labeled P. marinus cells in fixed oyster tissue in a species-specific manner.



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