Effect of C:N Ratio on Gamma-linolenic Acid Production by Mucor circinelloides Grown on Acetic Acid

Abstract

Summary The effect of different carbon to nitrogen (C:N) ratios, using acetic acid as carbon substrate, on the growth and production of gamma-linolenic acid (GLA) by Mucor circinelloides CBS 203.28 was examined in fed-batch cultures operated in pH-stat mode with an acetic acid/(NH4)2SO4 solution as titrant. With an increase in the C:N ratio of the feed from 20:1 to 100:1, the final biomass concentration and the percentage of GLA in the neutral lipid fraction decreased. However, the concomitant large increase in the crude oil content of up to 31% of the dry biomass resulted in the intracellular GLA content increasing from a value of 13 to 38.6 mg/g biomass. Increasing the C:N ratio also resulted in an increase in the neutral lipid fraction of the oil with a decrease in the glyco- and phospholipid fractions. The highest GLA concentration of 0.51 g/l culture, a biomass concentration of 23.4 g/l and a GLA content of 22.6% in the neutral lipid fraction was found when using a C:N ratio of 25:1, but with a relatively low GLA content of 21.7 mg/g biomass and a crude oil content of only 11.2%. The respiratory quotient stabilized at a value of about 1.1, suggesting that the glyoxylate shunt was not significantly active relative to the total carbon flux during the lipid accumulation phase.