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Title: ARACHIDONIC ACID SYNTHETIC PATHWAYS IN THE OYSTER PROTOZOAN PARASITE PERKINSUS MARINUS: EVIDENCE OF USAGE OF A DELTA-8 PATHWAY

Author
item CHU, FU-LIN - VA INST. OF MARINE SCI.
item LUND, ERIC - VA INST. OF MARINE SCI.
item HARVEY, ELLEN - VA INST. OF MARINE SCI.
item ADLOF, RICHARD

Submitted to: Molecular and Biochemical Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2003
Publication Date: 1/1/2004
Citation: Chu, F.E., Lund, E.D., Harvey, E., Adlof, R.O. 2004. Arachidonic acid synthetic pathways in the oyster protozoan parasite Perkinsus marinus: Evidence of usage of a delta-8 pathway. Molecular and Biochemical Parasitology. 133:45-51.

Interpretive Summary: Diseases caused by parasitic species of the genus, Perkinsus, in bivalve mollusks are world wide problems. The parasite, Perkinsus marinus (Dermo) is one of the two important protozoan parasites causing severe mortality in the American (eastern) oyster, Crassostrea virginica, on the U.S. east and Gulf coasts since the 1950s. Previously, no information existed on lipid metabolism and biosynthesis in this parasite, although its host is an ecologically and economically important aquatic species. The ability of P. marinus to synthesize arachidonic acid (AA) is novel. No other parasitic protozoans have been reported to have such a capability. The parasite was fed tagged fats and their metabolism (uptake and conversion) to AA followed. The in-depth understanding of the significance of de novo lipid and FA synthesis in P. marinus and its relationship to the parasite's development, life cycle completion, disease transmission and pathogenesis of the host obtained from this study should provide a useful model for development of drugs targeting lipid metabolic pathways. These drugs could help control disease in oyster acquaculture production, with potential applications to other bivalve species and even to humans.

Technical Abstract: The meront stage of the oyster protozoan parasite, Perkinsus marinus, is capable of synthesizing saturated and unsaturated fatty acids including the essential fatty acid, arachidonic acid [AA; 20:4(n6)]. Eukaryotes employ either delta-6 or delta-8 desaturase pathway or both to synthesize AA. To elucidate the arachidonic acid synthetic pathways in P. marinus, meronts were incubated with deuterium-labeled precursors 18:1(n9)-d6, 18:2(n6)-d4, 18:3(n3)-d4, and 20:3(n3)-d8. The lipids were extracted, converted to fatty acid methyl esters and analyzed using gas chromatography/mass spectrometry and gas chromatography/flame ionization detection. Labeled 18:2(n6), 20:2(n6), 20:3(n6) and 20:4(n6) were detected in meront lipids after 1, 3, 5 and 10 days incubation with 18:1(n9)-d6. Labeled 20:2(n6), 20:3(n6) and 20:4(n6) were found in lipids from meronts after incubation with 18:2(n6)-d4. No labeled 18:3(n-6) was detected in either incubation. Apparently, when incubated with 18:1(n-9)-d6, the parasite first desaturated 18:1(n9)-d6 to 18:2(n6)-d6 by delta-12 desaturase, then to 20:2(n6)-d6 by elongation, and ultimately to 20:3(n6)-d6 and 20:4(n6)-d6 using sequential delta-8 and delta-5 desaturation. Similarly, when incubated with 18:2(n6)-d4, P. marinus converted the 18:2(n6)-d4 to 20:2(n6)-d4 by elongation, to 20:3(n6)-d4 by delta-8 desaturase, and then to 20:4(n6)-d4 by delta-5 desaturase. These results provide evidence that P. marinus employs the delta-8 rather than the delta-6 metabolic pathway for arachidonic acid synthesis and, by development of specific drugs targeting this metabolic pathway, a useful model for control of this parasite in oysters and, potentially, for control of diseases caused by Perkinsus spp. in other bivalve species.