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Abstracts
Workgroup: Frontiers in Disease Research
Acid phosphatase(s): a virulence factor of the protozoan parasite, Perkinsus marinus, against host oyster's defense?
Principal Investigator(s):
Fu-Lin E. Chu, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA, mailto:chu@vims.edu
Funding Period: 09/01/96 to 08/31/97
The objectives of the one-year project were to biochemically and physiologically characterize Perkinsus marinus acid phosphatase and other antioxidant enzymes and determine the effects of temperature and salinity on the acid phosphatase secretion from P. marinus. During the one-year funding period, we determined 1. The extra- and intra-cellular antioxidant enzymatic activities in different strains of P. marinus; 2. Effect of temperature and salinity on the secretion of acid phosphatase from P. marinus; and 3. The intra-cellular and distribution of acid phosphatase in P. marinus. The extra- and intra-cellular activities of acid phosphatase (AP), superoxide dismutase (SOD), catalase, and glutathione peroxidase (GP) were examined in six different P. marinus strains/isolates, i.e., Delaware Bay, New Jersey (DB-NJ), Mobjack Bay, Virginia (MB-VA), Barataria Bay, Louisiana (BB-LA), Laguna Madre, Texas (LM-TX), Oxford, Maryland (OX-MD), and York River, Virginia (YR-VA). It was found that no calatase or GP was detected in P. marinus meront cells and the extra-cellular product (ECP). The YR-VA strain had significantly higher extracellular AP activities (units/mg cell protein) than all other strains. Intracellular AP activity was low (<1.0 unit/mg total cell protein) in all strains. LM-TX strain had the greatest intracellular AP activity. The mean SOD activity (ng SOD/mg total cell protein) was higher in the YR-VA strain, but statistically insignificant from the other strains. SOD activity was detected only in the culture media of 97 days old P. marinus culture. The effects of temperatures (4, 12, 20, and 28ƒC) and osmolality (400, 570, 840 mOsm/kg; equivalent to 14, 20, and 28 ppt) were investigated. AP secretion by P. marinus meronts was found to be cell density dependent and increased with increased culture temperatures and cell proliferation. AP secretion was similar in P. marinus cultured at 400 and 570 mOsm/kg media, but higher than P. marinus cultured at 870 mOsm/kg media. Results of the ultrastructural study revealed that intense AP activity was in the nucleus of the parasite. Based on its distribution in the nucleus, AP may be playing a role in events leading to cell cycle regulation. Although, it is still unclear whether AP in P. marinus plays a role in suppressing the host defense, it was discovered that no production of reactive oxygen intermediates (ROIs), toxic metabolites, was elicited when oyster hemocytes were challenged with P. marinus. Additionally, chemiluminescence (a measurement of ROI production) evoked from zymosan (yeast)-stimulated hemocytes was suppressed (reduced) when treated with live P. marinus meronts and ECP.
IMPACTS and/or BENEFITS:
Results of the study provide important information for a better understanding of the biochemistry, physiology and the virulence of the oyster parasite, Perkinsus marinus. It was a first study on the characterization of acid phosphatase and potential antioxidant enzymes in P. marinus and their roles in interfering and modulation of host defense. Via this study, it was first discovered that P. marinus cells and ECP were capable of suppressing host respiration burst, production of reactive oxygen intermediates, although the exact mechanism behind the ROI suppression by P. marinus remains to be elucidated. Results of the study have been presented in both international and national professional/scientific conferences/workshops and reported in two publications in renowned scientific journals. Currently an additional manuscript is in preparation and will be submitted for publication.
PROJECT PUBLICATIONS:
Volety, A. K. and F.-L. E. Chu. 1997. Acid phosphatase activity in Perkinsus marinus, the protistan parasite of the American oyster, Crassostrea virginica. J. Parasitol., 83:1093-1098.
Volety, A. and F.-L. E. Chu. 1995. Suppression of chemiluminescence of eastern oyster (Crassostrea virginica) hemocytes by the protozoan parasite, Perkinsus marinus. Dev. Com. Immunol. 19:135-142.
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