High cell density mixotrophic culture of Spirulina platensis on glucose for phycocyanin production using a fed-batch system

Abstract

A mixotrophic culture might be used as an alternative to conventional photoautotrophic mass culture systems for production of high value chemicals and pharmaceuticals by Spirulina platensis. The possibility of using mixotrophic culture to achieve high cell densities and phycocyanin productivities was investigated using fed-batch culture in a 3.7-l fermentor. In fed-batch cultures, the highest cell concentration of 10.24 g l −1 (dry weight) and the highest phycocyanin production of 795 mg l −1 were achieved which were much higher than those reported in the literature. The highest biomass concentration and phycocyanin production in the mixotrophic fed-batch culture were 5.1-fold and 2.8-fold, respectively, of that obtained in the photoautotrophic batch culture using the same fermentor. The cellular phycocyanin content was enhanced with increasing photosynthetic activities. In the photoautotrophic batch culture, the phycocyanin content was constant at approximately 135 mg g −1 dry cells throughout the course of cultivation. In contrast, in the mixotrophic batch culture, the phycocyanin content was not constant. It increased from 54 mg g −1 to 125 g −1 dry cells during the course of cultivation presumably due to the continuous changes of heterotrophic to photoautotrophic domination. These results suggest that the maximum phycocyanin production should occur at the best combination of cell densities and photosynthetic activities in mixotrophic fed-batch cultures of the microalga.