Sugar-based growth, astaxanthin accumulation and carotenogenic transcription of heterotrophic Chlorella zofingiensis (Chlorophyta)

The green microalga Chlorella zofingiensis can grow and produce the ketocarotenoid astaxanthin in the dark with glucose as sole carbon and energy source. In the present study, we reported that glucose, mannose, fructose, sucrose, galactose and lactose could differentially support the cell growth and astaxanthin biosynthesis. Of the sugars surveyed, glucose and mannose were the best carbon sources for the algal growth in the dark, as indicated by the relatively high specific growth rates (ca. 0.03 h(-1)) and high cell dry densities (ca. 10 g l(-1)). Furthermore, the algal cells cultured with glucose and mannose accumulated the highest amounts of astaxanthin (ca. 1 mg g(-1)), indicating a correlation between cell growth and astaxanthin formation. In addition, various sugars differentially regulated the transcription of three carotenogenic genes encoding phytoene desaturase (PDS), beta-carotene ketolase (BKT), and beta-carotene hydroxylase (CHYb) respectively. By using glucose fed-batch fermentation, high cell dry weight concentration (ca. 53 g l(-1)) and high astaxanthin production (ca. 32 mg l(-1)) were obtained, which are much higher than those ever reported in the alga. The present study suggests that C. zofingiensis is suitable for the production of natural astaxanthin on a massive scale. (C) 2008 Elsevier Ltd. All rights reserved.