Self-cycling fermentation of a citric acid producing strain of Candida lipolytica

Abstract

Self-cycling fermentation (SCF) is a technique used to cultivate synchronous populations of cells. The present work applied SCF to a citric acid producing strain of Candida lipolytica. Extremely stable, reproducible patterns of growth were achieved with a high level of cell synchrony (synchrony index=0.82). Synchrony was maintained, even when the individual cycle times were extended past the point of depletion of the limiting nutrient, demonstrating that SCF can be operated with cycle times significantly longer than the double time of the microorganism. Furthermore, the doubling time of the cells was independent of the cycle time and remained constant even at the longest cycle times. This technique resulted in a full order of magnitude increase in the biomass production rate compared to literature values. This biomass was found to be suitable for the production of citric acid in a second stage reactor. This second stage was not optimized but the citric acid production rate was comparable to rates found in the literature. These preliminary results indicated that this two stage system would lead to at least a five fold increase in actual citric acid production compared to conventional batch reactors of the same size.