Effects of CO(2) Concentration during Growth on Fatty Acid Composition in Microalgae

The degree of unsaturation of fatty acids was higher in Chlorella vulgaris 11h cells grown with air (low-CO₂ cells) than in the cells grown with air enriched with 2% CO₂ (high-CO₂ cells). The change in the ratio of linoleic acid to α-linolenic acid was particularly significant. This change of the ratio was observed in four major lipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylcholine, and phosphatidylethanolamine). The relative contents of lipid classes were essentially the same both in high-CO₂ and low-CO₂ cells. After high-CO₂ cells were transferred to low CO₂ condition, total amount of fatty acids remained constant but the relative content of α-linolenic acid increased during a 6-hour lag phase in growth with concomitant decreases in linoleic and oleic acids. When low-CO₂ cells were transferred to high CO₂ condition, total amount of fatty acids and relative content of oleic acid increased significantly. The amount of α-linolenic acid remained almost constant, while the amounts of palmitic, oleic, and linoleic acids increased. Similar, but smaller, changes in fatty acid compositions were observed in two species of green algae Chlamydomonas reinhardtii and Dunaliella tertiolecta. However, no difference was found in Euglena gracilis, Porphyridium cruentum, Anabaena variabilis, and Anacystis nidulans.