Advances in Synthetic Strategies for Microalgal Carotenoid Enhancement and Emerging Applications.

Carotenoids are increasingly studied for their robust antioxidant capacity, anti-inflammatory potential, protective vision and validated contribution to human health. Carotenoids are mainly obtained through chemical synthesis and plant extraction, which results in relatively high costs for producing carotenoids. However, microalgae represent a sustainable and high-yield platform for natural carotenoid production, with advantages including rapid growth, high pigment accumulation, and broad environmental adaptability. This review summarizes recent biotechnological advances in enhancing carotenoid production, with a focus on metabolic engineering, environmental regulation, and cultivation strategies. CRISPR/Cas9 enables precision metabolic pathway engineering, while environmental factors like light, nutrients, and stress significantly influence yield. Different cultivation strategies allow carotenoids to fulfill commercial or research needs. The two-stage strategy achieves rapid biomass increase during the growth stage, then shifts to accumulate carotenoids. This regulatory mode significantly reduces cell death by continuous stress, providing high productivity and stability in large-scale production. Carotenoids participate in many innovative applications across various fields, including treatments in medicine, skin protection in cosmetics, protein stabilization in foods, enhancing animals' survival and so on. Future research will integrate bioprocess optimization, precision strain engineering, and adaptive environmental strategies to scale high-value microalgal carotenoid production as a commercially and environmentally viable solution.