Multi-omics insights of biotin-enhanced astaxanthin and total fatty acid productivity in heterotrophic Chromochloris zofingiensis under stress conditions

Astaxanthin is a secondary carotenoid which predominantly accumulates under abiotic stresses at the expense of cell growth. Functioning as an essential cofactor for carboxylase enzymes, biotin has been demonstrated to significantly enhance cellular stress resistance. This study explores the effects of exogenous biotin supplementation on the growth, astaxanthin, and total fatty acid (TFA) production in Chromochloris zofingiensis under nitrogen deficiency (ND) and high salt stress (HS). Exogenous biotin significantly improved biomass accumulation with the reduced reactive oxygen species (ROS) level under both stresses. At a concentration of 1000 μg L⁻¹, the maximal dry weight (DW) and astaxanthin content were achieved, which resulted in the highest astaxanthin yield as 3.29-fold and 2.61-fold of that in the respective controls under ND and HS conditions. Besides, biotin also enhanced TFA yield by 54 % and 36 % under ND and HS conditions, respectively. Integrated transcriptomic and metabolomic analyses demonstrated that biotin significantly enriched pathways related to amino acid metabolism, lipid, and carbohydrate metabolism under ND; whereas pathways associated with energy metabolism and carotenoid biosynthesis under HS. Biotin modulated the expression of key genes in carotenoid biosynthesis (PSY, PDS, ZDS, CrtZ) and fatty acid biosynthesis (FabH, FabG), demonstrating its role in fine-tuning these metabolic pathways. This study establishes biotin as a potent regulator of simultaneous astaxanthin and fatty acid accumulation in C. zofingiensis under stress conditions.