REASSESSMENT OF LIPID-COMPOSITION OF THE DIATOM, SKELETONEMA-COSTATUM

In the present work, we questioned the natural or artifactual origin o f the large amounts of free fatty acids recovered in lipids from the d iatom Skeletonema costatum. Using rapid cell harvest and a very drasti c method to extract the lipids, we demonstrated that these lipid patte rns rich in free fatty acids were relevant to the degradation of compl ex lipids. A revised lipid composition of S. costatum is given which d iffers from those previously described by the absence of free fatty ac ids, while the proportion of polar lipids is substantially increased. Membrane lipids are mostly represented and storage lipids are less abu ndant, since we analysed the cells during their exponential growth pha se. However, the fatty acid composition is in agreement with previous data. Polyunsaturated fatty acids (PUFA) consist essentially of 20:5 o mega 3, 16:3 omega 4 and 16:4 omega 1, while 16:1 omega 7 is the main monounsaturated FA. This confirms that, with regard to its lipid compo sition, the diatom, S. costatum, provides a good diet for molluscs, pa rticularly through its high proportion of omega 3 PUFA. Using this ext raction procedure, sterols were found to be identical to previous resu lts but a new compound, a 18:1 fatty alcohol, was detected. The conseq uences of this reassessement on the lipid compositions of diatoms so f ar published and their application to the lipid diet of mollusc larvae in aquaculture are discussed.