LIPID-COMPOSITION OF THE TOXIC MARINE DIATOM, NITZSCHIA-PUNGENS

A bloom of Nitzschia pungens f. multiseries was the source of domoic acid in mussels which caused an outbreak of amnesic shellfish poisoning in Canada. Because algal lipid and fatty acid production is known to vary during blooms we examined the lipid content, the lipid class composition and the fatty acid composition of N. pungens grown under nutrient-replete and silicon-limited conditions. The total lipid content ranged from 13 to 30 pg per cell; the major lipid classes were polar lipids (including phospholipids) and free fatty acids. GC analysis of total fatty acid methyl esters showed that the proportion of total dienes, trienes and tetraenes increased with silicon limitation at the expense of saturated fatty acids. N. pungens had unusually high contents of 16:4nl which increased with silicon limitation to 11 +/- 1% of the total fatty acids. High proportions of this polyunsaturated fatty acid may thus be a useful marker of N. pungens in natural plankton blooms and associated food web organisms. Lipids extracted from cultured N. pungens may also be a useful source of 16:4nl for biomedical studies.