High yield production of lutein by heterotrophic Chlorella protothecoides in fed-batch systems

Abstract

Heterotrophic cultivation of Chlorella protothecoides was carried out in a 3.7–1 fermentor in batch mode with initial concentrations of 40 g/l glucose and of 3.6 g/l urea until late exponential phase when concentrated nutrients containing glucose and urea were fed into the culture, in which the nitrogen source was sufficient compared to carbon source and a maximum biomass concentration of 48.0 g/l (on a dry weight basis) was achieved. This biomass concentration was 28.4 g/1 higher than that observed in batch culture under the same conditions at the initial cultivation stage. In another cultivation run, the culture was provided with the same initial concentrations of glucose and urea as above in the batch mode, followed by a relatively reduced supply of nitrogen source in the fed-batch mode to establish a nitrogen-limited culture. Such a modification resulted in an enhanced lutein production without significantly lowering biomass production. The cellular lutein content in this process was 0.27 mg/g higher than that obtained in the N-sufficient culture. This improvement was also reflected by higher values of maximum lutein yield, lutein productivity and lutein yield coefficient on glucose. This N-limited fed-batch culture was successfully scaled up from 3.7 1 to 30 1, and a three-step cultivation process was developed for the high yield production of lutein. The maximum biomass concentration (45.8 g/1 dry cells) achieved in the large fermentor (30 1) was comparable to that in the small one (3.7 1). The maintenance of this culture at a higher temperature (i. e., 32 °C) for 84 h resulted in a 19.9% increase in lutein content, but a 13.6% decrease in biomass concentration. This enhancement of lutein production resulted from the combination of nitrogen limitation and high temperature stress.