Acyl lipid composition variation related to culture age and nitrogen concentration in continuous culture of the microalga Phaeodactylum tricornutum

The influence of culture age and nitrogen concentration on the distribution of fatty acids among the different acyl lipid classes has been studied in continuous cultures of the microalga Phaeodactylum tricornutum. The culture age was tested in the range of 1.15-7 days, controlled by adjusting the di lution rate of fresh medium supplied. The effect of nitrogen concentration was tested from saturating conditions to starvation by modifying nitrate co ncentration in the fresh medium. Culture age had almost no influence on the fatty acid content; 16:0, 16:3 and 20:5 increased moderately wherein the l evel of 16:1 decreased when the culture age decreased. Culture age had no e ffect on the total fatty acid content that remained around 11% of dry weigh t. Conversely, culture age had a greater impact on lipid classes, producing changes in amounts of triacylglycerols (TAG) which ranged between 43% and 69%, and galactolipids (GLs) that oscillated between 20% and 40%. In genera l, the content of polar lipids of the biomass decreased with culture age. T he other factor assayed, nitrogen content, affected the fatty acid profile. Saturated and monounsaturated fatty acids accumulated when the nitrogen co ncentration was decreased. The experiments regarding the effect of nitrogen concentration on lipid species were carried out with cells of an average a ge of 3.5 days. A decrease of the nitrogen concentration caused the GL frac tion to decrease from 21 to 12%. Conversely, both neutral lipids (NLs) and phospolipids (PLs) increased from about 73 to 79% and from 6 to 8%, respect ively. In these experiments, TAG was the lipid class with the highest incre ase, from 69 to 75%. (C) 2000 Elsevier Science Ltd. All rights reserved.