Mechanism(s) of long chain n-3 essential fatty acid production in two species of heterotrophic protists: <Emphasis Type="Italic">Oxyrrhis marina</Emphasis> and <Emphasis Type="Italic">Gyrodinium dominans</Emphasis> |
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Authors: | Eric D Lund Fu-Lin E Chu Ellen Harvey Richard Adlof |
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Institution: | (1) Virginia Institute of Marine Science, College of William and Mary, P. O. 1346, Gloucester Point, VA 23062, USA;(2) USDA, ARS, NCAUR, 1815 N. University, Peoria, IL 61604, USA |
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Abstract: | As intermediaries, some heterotrophic protists can enhance the content of the long chain n-3 essential fatty acids (LCn-3EFAs),
eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), of low food quality algae for subsequent use at higher trophic
levels. However, the mechanisms that produce LCn-3EFAs are presently unknown, although LCn-3EFA production by heterotrophic
protists at the phytoplankton–zooplankton interface may potentially affect the nutritional status of the pelagic system. We
investigated whether the heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans, produce LCn-3EFAs via elongation and desaturation of dietary LCn-3EFA precursors and/or synthesize LCn-3EFAs de novo by:
(1) feeding the two heterotrophic protists with a prey deficient in n-3 fatty acids, (2) incubating them in medium containing
13C-labeled sodium acetate, and (3) feeding the two protists gelatin acacia microspheres (GAMs) containing a deuterium-labeled
LCn-3EFA precursor, linolenic acid 18:3(n-3)-d4]. Both O. marina and G. dominans synthesized EPA and DHA when fed the n-3 fatty acid-deficient prey, Perkinsus marinus, a parasitic protozoan. O. marina, but not G. dominans utilized 13C-labeled acetate from the medium to produce uniformly labeled fatty acids, including DHA. Both heterotroph species consumed
GAMs containing 18:3(n-3)-d4 and catabolized 18:3(n-3)-d4 to 16:3(n-3)-d4 and 14:3(n-3)-d4, while no 20 or 22 carbon metabolites
of 18:3(n-3)-d4 were detected. These results suggest that O. marina and G. dominans do not elongate and desaturate dietary LCn-3EFA precursors to produce LCn-3EFAs, but rather they produce LCn-3EFAs de novo,
possibly via a polyketide synthesis pathway. |
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