Synergistic Application of Cytidine Monophosphate and Sodium Chloride for Enhanced Co-Production of Astaxanthin and Fatty Acids in Haematococcus lacustris Motile Cells Under High-Light Stress

This study evaluated the synergistic effects of sodium chloride (NaCl) and cytidine monophosphate (CMP) on enhancing the co-production of astaxanthin and fatty acids while suppressing secondary cell wall (SCW) formation in Haematococcus lacustris (synonym: H. pluvialis) under high-light stress. An orthogonal design identified the optimal combination (0.5 g/L NaCl and 0.5 mM CMP), which significantly increased astaxanthin yield by over 35.6% and total fatty acid yield by 28%, while maintaining 96.8% of cells in motile state (SCW-deficient). Physiological analyses revealed elevated reactive oxygen species levels, concomitant with higher actual photochemical efficiency (Fv′/Fm′) and relative electron transport rates II (rETR(II)) along with enhanced non-photochemical quenching (NPQ) capacity, and metabolic reprogramming characterized by the accumulation of lipids, sugars, and starch alongside decreased protein yield. Metabolomics indicated reduced carbon supply for SCW polysaccharide biosynthesis, coupled with decreased protein yield and altered amino acid profiles characteristic of nitrogen-limited metabolism, which collectively favored the reallocation of carbon resources toward nitrogen-free high-value products. Transcriptomics confirmed the downregulation of SCW component biosynthetic genes and the upregulation of the methylerythritol phosphate (MEP) pathway and astaxanthin biosynthetic pathway. Scale-up experiments validated this strategy for producing astaxanthin-rich motile cells, offering a promising approach for microalgal biorefinery.