Glucose triggers cell structure changes and regulates astaxanthin biosynthesis in Chromochloris zofingiensis

Heterotrophic cultivation of Chromochloris zofingiensis is considered as a promising means of astaxanthin production; however, the astaxanthin content in heterotrophic cells is generally lower than that in photoautotrophic cells. To address this issue, the regulatory effects of glucose on astaxanthin accumulation were investigated. We found that glucose could increase astaxanthin accumulation by elevating the gene expression of PSY, LCYb, CHYb and BKT within 24 h; however, after 24 h, expression of those genes in the control group was higher than that in the glucose group, leading to an increased astaxanthin content in the control group after 48 h. At 96 and 192 h, the astaxanthin contents in the control group were 1.26 and 1.27 times of those in the glucose group, respectively. Further investigation showed that, glucose treatment triggered a decrease in chlorophylls content, caused degradation of chloroplasts at 24 h, which may be the reason for the above variation in gene expression and that in astaxanthin accumulation. Moreover, glucose also caused a slight increase in total fatty acid content and altered cellular lipid composition. Collectively, these findings suggested that glucose may regulate astaxanthin accumulation through its influence on cell structure.