LIPID-COMPOSITION OF EUGLENA-GRACILIS IN RELATION TO CARBON-NITROGEN BALANCE

The lipid class and fatty acid compositions of Euglena gl acilis were analysed after growth under various conditions of autotrophy or photoh eterotrophy, in order to identify the contribution of lactate (a carbo n source) and ammonium phosphate (a nitrogen source) to the metabolism of these compounds. When ammonium and lactate were both present in th e medium, in concentrations that allowed growth, the lipid composition of algae appeared to be independent of the ammonium concentration. Th e effects of increasing ammonium phosphate concentration on lipid meta bolism were observed only when lactate was depleted. With increasing n itrogen concentration in the medium, an increase in the content of gal actolipids rich in polyunsaturated C-16 and C-18 fatty acids (FA) was noted, as well as an increase in the monogalactosyldiacylglycerol : di galactosyldiacylglycerol ratio; these changes could be related to an i ncrease in the number of the stacked lamellae present in chloroplasts. Nitrogen concentration had no influence on the C-12 and C-14 FA but i nduced a loss of C-22 FA. In the absence of ammonium phosphate in the culture medium, increasing lactate concentrations were accompanied by a decrease in all plastid lipids, whereas the content of storage lipid s (enriched in 14:0 and 16:0) increased. Partial inhibition of the pol ydesaturation of C-18 FA was observed and was accompanied by an accumu lation of 18:1.