Lipids of Cunninghamella echinulata with emphasis to γ-linolenic acid distribution among lipid classes

Changes in lipid composition of the oleaginous fungus Cunninghamella echinulata were monitored during growth. Lipid fractions and individual lipid classes varied in amount, relative proportions, and fatty acid profile depending on the developmental stage. Neutral lipids (N), comprised mainly of triacylglycerol, were accumulated in the fungal mycelium during both the late exponential and the stationary growth phases with a concomitant decrease in the amount of polar lipids. While fatty acid composition of N fraction remained almost constant, individual N classes showed a noticeable alteration in gamma-linolenic acid (GLA) concentration. The glycolipid plus sphingolipid (G+S) fraction consisted mainly of monoglycosylglycerol and diglycosylglycerol. The sugar composition of G+S fraction was analyzed and showed a partial replacement of galactose for glucose as growth proceeded. Phospholipid (P) major classes were phosphatidylcholine (PC) and phosphatidylethanolamine, followed by phosphatidylinositol, phosphatidylserine, and diphosphatidylglycerol. P fatty acid composition showed significant changes with time, resulting in a considerable drop in the unsaturation index of this fraction. While in mid exponential growth phase, all P classes contained more than 20% w/w GLA of total fatty acids, and their concentration decreased to 12-17% w/w, except for the PC class where GLA concentration remained at high levels (e.g., more than 20% w/w). The constant level of GLA in PC at all growth phases suggests that PC was the major source of GLA. Sterol analysis showed that their concentration increased during growth, whereas ergosterol was the major component.