A mixotrophic preculture strategy enhances biomass and astaxanthin productivity of Chromochloris zofingiensis

Abstract

Abstract Background Chromochloris zofingiensis is a competitive potential source of natural astaxanthin, as the alternative of Haematococcus pluvialis. However, its intracellular astaxanthin synthesis is inhibited under heterotrophic mode, which impedes the establishment of its ultra-high-density cultivation for astaxanthin industrial production. Results Preculture can provide a buffer for cells to acclimate drastic condition transformations and achieve a greater physiological state. An original mixotrophic preculture (MP) strategy established in this study successfully increased the heterotrophic biomass concentration of C. zofingiensis up to 121.5 g L− 1 in a 20 L fermenter, surpassing the highest high-density record. Meanwhile, the astaxanthin productivity achieved 0.111 g L− 1 day− 1, which is 7.3-fold higher than the best record of C. zofingiensis, and even exceeded that of H. pluvialis. The molecular mechanisms of C. zofingiensis under MP were further investigated using carbon partitioning model, transcriptome, and 13C tracer-based metabolic flux analysis. The results revealed that MP promoted protein degradation for lipid synthesis under heterotrophic cultivation. It also enhanced the expression of genes related to central carbon metabolism, thus providing sufficient energy for biomass accumulation. The metabolic flux to lipids and carotenoids under MP was elevated, providing abundant precursors for astaxanthin biosynthesis. Conclusions This study firstly proposed a MP strategy to regulated the physiological state of C. zofingiensis cells before fermentation, thus realized its heterotrophic high-density growth and increase the astaxanthin yield on a pilot scale. This strategy exhibits great potential to be utilized in astaxanthin industrial production and more microalgal related industry.