Biosynthesis of Lipids by Kinetoplastid Flagellates

Crithidia fasciculata, Crithidia oncopelti, Crithidia luciliae, Crithidia sp. from Arilus cristatus, Crithidia acanthocephali, Blastocrithidia culicis, Leishmania tarentolae, and Leptomonas leptoglossi were grown under axenic conditions in chemically defined media, and their fatty acids were determined. Palmitic, stearic, and a C19 cyclopropane acid were the major saturated fatty acids. Oleic, linoleic, and γ-linolenic were the major unsaturated fatty acids. α-Linolenic acid could not be detected in any of these organisms. Monounsaturated fatty acids were synthesized by direct oxidative desaturation of the corresponding saturated acids, and polyunsaturated fatty acids were synthesized by progressive desaturation and chain elongation of the monoenoic acids. The major lipids of C. fasciculata and C. oncopelti— triglycerides, sterol esters, phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine—were identical. Phosphatidylethanolamine contained the bulk of the cyclopropane acid found in C. fasciculata. Ergosterol was the major sterol of Crithidia, Blastocrithidia, and Leishmania species. Methionine served as a source of methyl groups for the biosynthesis of both ergosterol and the cyclopropane acid.