Commercial sugars as substrates for lipid accumulation in Cunninghamella echinulata and Mortierella isabellina fungi

Cunninghamella echinulata and Mortierella isabellina, fungi capable of accumulating single cell oil (SCO) containing gamma-linolenic acid (GLA), were cultivated on sugar-based media, at initial substrate concentration 60 g/L. It was demonstrated that the carbon source plays an essential role on lipid accumulation process. Especially, on glucose, C. echinulata produced 3.9 g/L lipids containing 19.5% GLA, whereas M. isabellina achieved 9.9 g/L of lipid, containing 3.5% GLA. Growth on fructose was also satisfactory for both microorganisms. Although M. isabellina failed to grow adequately on saccharose, C. echinulata presented appreciable biomass production of 17.6 g/L, containing 18% of fat. Extra-cellular invertase activity was also detected in the case of C. echinulata cultures, achieving 0.5 U/mL. Both molds presented satisfactory growth on molasses, with significant amounts of SCO and GLA produced, accompanied by non-negligible substrate decolorization. Scaling-up in a 3-L bioreactor of M. isabellina with glucose as a substrate resulted in 17.5 g/L of biomass, containing 12.7 g/L of lipid. Finally, fractionation of cellular lipid for both strains showed that neutral lipids represented about 90-92% w/w upon total accumulated lipids, whilst fractions of glycolipids plus sphingolipids and phospholipids were 6-7 and 3-4%, respectively.