Lipid class specific production of EPA and DHA in Phytoplankton Dinoflagellate Heterocapsa Triquetra

Abstract

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are dietary polyunsaturated fatty acids (PUFA) with a range of health benefits. Phytoplankton are the primary marine producers of EPA and DHA through the process of photosynthesis. Measuring the effect of light intensity and temperature variation on the production of PUFA was the purpose of this study. Heterocapsa triquetra, a dinoflagellate, was the phytoplankton used in this study and its response to specific environmental conditions was compared to Phaeocystis globosa, a prymnesiophyte. H. triquetra were cultivated in two different light intensities (88 and 140 µmol photons m-2 s-1) having the same temperature (24 oC) and another light intensity with a different temperature (210 µmol photons m-2 s-1 and 14 oC). For comparison with a different species, P. globosa was grown at the same condition as one of the H. triquetra (140 µmol photons m-2 s-1and 24 oC). Spikes of 99% NaH13CO3 were added and after 6 h, cultures were harvested. Lipid classes were identified and quantified by high performance liquid chromatography (HPLC), FA proportions were measured with gas chromatography flame ionization detection (GCFID), and incorporation of 13C in FA was measured by gas chromatography mass spectroscopy (GCMS).

Decreasing light intensity increased the production of DHA in digalactosyldiacyl glycerol (DGDG), while decreasing the production of DHA, 18:5n-3, and 18:3n-3 in triacylglycerol (TAG) in H. triquetra. Lowering the temperature allowed the measurement of production of DHA in DGDG even though a higher light intensity was used, thereby proving that lowering the temperature can possibly increase production rates of PUFA in DGDG. P. globosa grown under the same conditions as H. triquetra (24 oC, and 140 µmol photons m-2 s-1) was better labelled and had higher production of all PUFA in DGDG, and lower production of DHA, 18:4n-3 and 18:3n-3 in TAG, thus showing that different phytoplankton species respond to the same environmental conditions differently. This study conveys a feasible method to measure the rate of production of EPA and DHA in phytoplankton.