Lipid and fatty acid composition of the marine brown alga Dictyopteris membranacea

Glycerolipids and fatty acids of D. membranacea (Dictyotales) were analysed. The betaine lipid DGTA and the glycolipids MGDG, DGDG and SQDG were major components. The phospholipids PE, PG, PI and PHEG were present in minor amounts only. This lipid pattern, which is characterised by the presence of DGTA and the absence of PC, has been found exclusively in brown algae belonging to the orders Dictyotales, Durvillaeales and Fucales. Major fatty acids were 16:0, 18:1, 18:2, alpha 18:3, 18:4 and 20:4 acids. MGDG was the most unsaturated lipid with high levels of 18:4 acid. SQDG showed the highest degree of saturation containing a considerable proportion of 16:0 acid. DGTA contained 14:0, 18:1, 18:2 and 20:4 as major fatty acids. Among phospholipids, PE and PHEG had a very similar pattern which was enriched in 20:4 acid. Analysis of the positional distribution of fatty acids revealed that DGTA and MGDG were almost exclusively of the ''eukaryotic'' type, whereas SQDG was predominantly of the ''prokaryotic'' type. For the first time, molecular species of selected lipids have been analysed in a brown alga. In DGTA, 14:0/18:1, 14:0/18:2 and 14:0/20:4 were the main molecular species. In MGDG the highly unsaturated alpha 18:3/18:4, 18:4/18:4 and 18:4/20:5 were predominant.