De novo arachidonic acid synthesis in Perkinsus marinus, a protozoan parasite of the eastern oyster Crassostrea virginica.

The capability of synthesizing fatty acids de novo in the meront stage of the oyster protozoan parasite, Perkinsus marinus, was investigated employing stable-isotope-labeled precursors (1,2 13C-acetate and palmitic-d(31) acid). Fatty acid methyl esters derived from 1,2 13C-acetate and palmitic-d(31) acid were analyzed using gas chromatography/mass spectrometry and gas chromatography/flame ionization detection. Results revealed that in vitro cultured P. marinus meronts utilized 13C-acetate to synthesize a range of saturated and unsaturated fatty acids. The saturated fatty acids 14:0, 16:0, 18:0, 20:0, 22:0, 24:0 and the unsaturated fatty acids, 18:1(n-9), 18:2(n-6), 20:1(n-9), 20:2(n-6), 20:2(n-9), 20:3(n-6), 20:4(n-6) were found to contain 13C, after 7, 14, and 21 days incubation with the precursor. This indicates that meronts can synthesize fatty acid de novo using acetate as a substrate. Meronts efficiently elongated 16:0-d(31) to 18:0, 20:0, 22:0, 24:0, but desaturation activity was limited, after 7 and 14 days cultivation. Only a small quantity of 18:1-d(29) was detected. This suggests that meronts cannot directly convert exogenous palmitic acid or its products of elongation to unsaturated counterparts. The ability to synthesize 20:4(n-6) from acetate is particularly interesting. No parasitic protozoan has been reported to be capable of synthesizing long chain essential fatty acids, such as 20:4(n-6) de novo. Future study will be directed to determine whether the observed in vitro activities indeed reflect the in vivo activities, when meronts are associated with the host.