Turning the industrially relevant marine alga Nannochloropsis red: one move for multifaceted benefits.

Nannochloropsis oceanica is an industrially relevant marine microalga rich in eicosapentaenoic acid (EPA, a valuable ω-3 polyunsaturated fatty acid), yet the algal production potential remains to be unlocked. Here we engineered N. oceanica to synthesize the high-value carotenoid astaxanthin independent of high-light (HL) induction for achieving multifaceted benefits. By screening β-carotenoid ketolases and hydroxylases of various origins, and strategically manipulating compartmentalization, fusion patterns, and linkers of the enzyme pair, a remarkable 133-fold increase in astaxanthin content was achieved in N. oceanica. Iterative metabolic engineering efforts led to further increases in astaxanthin synthesis up to 7.3 mg g, the highest reported for microalgae under nonstress conditions. Astaxanthin was found in the photosystem components and allowed the alga HL resistance and augmented EPA production. Besides, we achieved co-production of astaxanthin and EPA by the engineered alga through a fed-batch cultivation approach. Our findings unveil the untapped potential of N. oceanica as a robust, light-driven chassis for constitutive astaxanthin synthesis and provide feasible strategies for the concurrent production of multiple high-value biochemicals from CO, thereby paving the way for sustainable biotechnological applications of this alga.