THE UTILIZATION OF SHORT-CHAIN MONOCARBOXYLIC ACIDS AS CARBON-SOURCESFOR THE PRODUCTION OF GAMMA-LINOLENIC ACID BY MUCOR STRAINS IN FED-BATCH CULTURE

The Fischer-Tropsch reaction water, which contains C-2 to C-5 monocarb oxylic acids, generated as a co-product of the Sasol industrial oil-fr om-coal process, constitutes a potential cheap carbon substrate for th e production of gamma-linolenic acid (GLA) by selected Mucor species. Three strains of Mucor were each grown in an air-lift reactor operated in a fed-batch, pH-stat mode under N-limitation with a mixture of C-2 to C-5 monocarboxylic acids as both pH titrant and carbon source. The production of GLA from this substrate was evaluated. Growth typically resulted in the rapid assimilation of acetic, n-butyric and n-valeric acids. Although propionic, iso-butyric and isovaleric acids were assi milated to varying degrees, these acids accumulated in the culture. Mu cor circinelloides CBS 203.28 gave the best results in that it assimil ated 36% to 100% of each acid, had a biomass yield coefficient of 0.3 (calculated on acids utilized), and contained 28% crude oil, 84% of wh ich comprised neutral lipids with a GLA content of 14.4%, giving 33 mg GLA/g biomass. GLA accumulation coincided with a decrease in the stea ric-acid content of the neutral-lipid fraction. The results were compa rable with previous results obtained with acetic acid and glucose as s ole carbon sources, demonstrating the feasibility of producing GLA fro m the above mixture of organic acids.