Positional distribution of fatty acids, and molecular species of polar lipids, in the diatom Phaeodactylum tricornutum

Each of the four main polar lipids from Phaeodactylum tricornutum UTEX 640, monogalactyosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylcholine (PC), was separated into its molecular species by reverse-phase HPLC, and the positional distribution of fatty acids in each species was determined. Numbers of separated peaks in each lipid class were: MGDG, 10; DGDG, 7; SQDG, 10; and PC, 11. Eicosapentaenoic acid (EPA) was present in 20 of the 45 molecular species but predominated in the MGDG and DGDG classes, where 13 of the proposed structures contained EPA. EPA was always located in the sn-1 position except in two lipid species, MG5 and PC2, where it was present at both the sn-1 and sn-2 locations. The predominant polar lipid molecular species found in P. tricornutum UTEX 640 were (mg total fatty acids per g dry weight of biomass) 20:5-16:4-MG, 41-2; 20:5-16:1-DG, 21.0; 16:1-16:1-SQ, 18-2; and 20:5-16: 1-MG, 18-0. [Structure indicates fatty acid at sn-1 position- fatty acid at sn-2 position-carbohydrate component at sn-3 position of the glycerol molecule. Abbreviations: 20: 5, EPA; 16: 4