A study of the histozoic oyster parasite, Perkinsus marinus: I. Disease processes in American oysters (Crassostrea virginica). II. Biochemistry of Perkinsus marinus

Numerous studies have investigated the disease processes of Perkinsus marinus in the oyster, Crassostrea virginica. However, the transmission dynamics and factors affecting P. marinus infection are still unclear. The objectives of this study were to investigate: (1) the principal and most effective lifestage of P. marinus, (2) the synergistic effects of temperature, salinity and P. marinus dose on disease prevalence, (3) suppression of host reactive oxygen intermediates by P. marinus, (4) the localization of acid phosphatase in the parasite, (5) the effects of temperature and salinity on acid phosphatase secretion, and (6) the P. marinus lipid and fatty acid composition. Meronts were more infective than prezoosporangia, and infectivity was dose dependent (100 cells minimum). High temperatures, salinities and P. marinus doses increased infection prevalence and intensity. Temperature was the most important factor influencing disease susceptibility, followed by cell dosage and salinity. Both temperature and salinity significantly affected the host cellular and humoral factors in oysters. P. marinus suppression of hemocyte reactive oxygen intermediates production, as assessed by chemiluminescence was dose dependent. Zymosan stimulated hemocyte chemiluminescence was reduced, suggesting that live P. marinus cells or their extra-cellular products suppress host reactive oxygen intermediates production. Acid phosphatase activity in P. marinus cells increased with increasing temperature. Meronts had higher acid phosphatase activity than prezoosporangia. Extracellular acid phosphatase secretion by P. marinus was dose dependent, increasing with temperature and osmolality. Electron microscopy revealed that acid phosphatase activity was localized primarily in the nucleus, but was also present in the cell membrane. Lipid classes of meronts resembled those found in their media. Phospholipids were the major lipid class in meronts, while triacylglycerols were dominant in prezoosporangia isolated from infected oyster tissue. Results indicated that meronts may be capable of interconversion of lipid classes. Both meronts and prezoosporangia had much higher levels of arachidonic acid than the host