Lipid composition during growth of motile and coccolith forms of Emiliania huxleyi

Abstract

Flagellated and coccolith cell types of Emiliania huxleyi were grown axenically and the lipid class and fatty acid compositions of the main polar lipid classes examined throughout the growth cycle. The lipid compositions of the two cell types were similar with only slight differences noted, the coccolith form tending to have higher levels of neutral lipids than the flagellate. Methyl and ethyl ketones were present in both cell types. The proportion of phospholipids and glycolipids increased during the log-phase, while neutral lipids (free fatty acids, triacylglycerols, ketones and hydrocarbons) achieved their highest levels in the late stationary-phase. The polar lipids of both cell types were very rich in polyunsaturated fatty acids (PUFA). In sulphoquinovosylglyercol + phosphatidylethanolamine, 18:3 n-3 and 18:4 n-3 were the predominant fatty acids totalling 42.4–55.7%, while 18:5 n-3 (33.1–79.2%) was the main fatty acid in digalactosyldiacylglycerols. This fatty acid was also predominant in monogalactosydiacylglycerols (36.6–57.7%), with lesser amounts of 18:4 n-3 and 22:6 n-3. Phosphatidylcholine was dominated by two molecular species, 22:6 n-3/22:6 n-3 and 14:0/22:6 n-3, accounting for 25.7–33.7 and 42.0–58.3%, respectively. Changes in PUFA composition over the growth cycle were small. The C 18 PUFA associated with thylakoid glycolipids tended to increase during the log-phase and decreased in the late stationary-phase while 22:6 n-3 peaked in the late stationary-phase. The results are discussed in relation to the ecology of this alga.