The crosstalk between astaxanthin, fatty acids and reactive oxygen species in heterotrophic Chlorella zofingiensis

Chlorella zofingiensis can achieve ultrahigh cell density under heterotrophic growth conditions and has been considered as a promising producer of astaxanthin. Astaxanthin is predominantly esterified with fatty acids, in the form of either mono-ester or di-ester. The interrelationship between astaxanthin and fatty acids remains poorly understood. In the present study, we found that astaxanthin induction was accompanied by fatty acid accumulation in the glucose-fed heterotrophic C. zofingiensis cells. The presence of cerulenin, a specific inhibitor against fatty acid biosynthesis, led to a significant increase in the content of astaxanthin, di-ester in particular. When treated with sesamol, which is known to inhibit intracellular NADPH supply, a considerable decrease in astaxanthin was observed, together with a slight drop in fatty acids. Reactive oxygen species (ROS) level was found to correlate well with astaxanthin content in C. zofingiensis regardless of culture conditions. Collectively, these findings suggest that astaxanthin biosynthesis may compete with fatty acids for the carbon precursors and reducing power, and NADPH supply is important for astaxanthin accumulation, which will help us better understand astaxanthin biosynthesis in heterotrophic C. zofingiensis and benefit the future engineering for astaxanthin production.