Our New Paper Published in Algal Research

Chlorella sorokiniana is capable of high-cell-density heterotrophic cultivation, endowing it with exceptional potential for large-scale, efficient lutein production. However, its industrial application has been hindered by low lutein content and the inability to precisely control carotenoid composition. To address these limitations, a chlorophyll-deficient and lutein-enriched yellow mutant C. sorokiniana MT03 was employed to investigate the effects of carbon–nitrogen (C/N) ratio modulation on lutein and protein production under heterotrophic conditions. Systematic optimization identified a C/N ratio of 16 as optimal, resulting in marked enhancement of both lutein and protein accumulation. Integrated physiological and transcriptomic analyses demonstrated that carbon depletion combined with nitrogen repletion coordinately regulated central carbon metabolism, macromolecular biosynthesis, heme homeostasis, and carotenoid biosynthetic pathways. Notably, key genes involved in fatty acid biosynthesis, starch degradation, amino acid biosynthesis, and carotenoid formation were significantly upregulated, highlighting the tight integration of nitrogen availability with carbon partitioning. Heme accumulation was found to enhance CYP97-mediated lutein synthesis, further linking nitrogen status to carotenogenic flux. A two-stage cultivation strategy, comprising (I) fed-batch growth for high-cell-density biomass production, followed by (II) carbon-depleted and nitrogen-replete conditions to trigger lutein and protein synthesis, was successfully implemented in a 5-L bioreactor. This approach yielded a final biomass concentration of 184.46 g/L, with volumetric titers of 481.63 mg/L lutein and 76.31 g/L protein, surpassing most values reported in the literature. These results demonstrate that rational C/N metabolic regulation effectively redirects carbon flux toward target metabolites, providing a scalable and industrially viable platform for the co-production of lutein and protein in microalgae.