Co-cultivation of Nannochloropsis salina and Xanthophyllomyces dendrorhous in mixed medium enhances lipid and antioxidant yields

The marine microalga Nannochloropsis salina and the red yeast Xanthophyllomyces dendrorhous are microbial cell factories with growing interest in the food, feed, and nutraceutical sectors, owing to their ability to synthesize valuable compounds such as omega-3 fatty acids, carotenoids, and antioxidants. In this study, both microorganisms were cultivated in a novel mixed culture system using a 1:1 combination of f/2 medium—originally designed for marine microalgae and prepared with seawater—and a potato extract–glucose medium (PE, 4 g/L and 20 g/L, respectively), aiming to identify conditions that support their simultaneous growth and enhance bioactive compound production. Growth parameters (optical density, pH, fluorescence) and metabolite profiles (biomass, total lipids, antioxidant activity, and polyphenols) were monitored. The mixed f/2 + PE medium supported both organisms, with balanced pH (∼6) and the coexistence of N. salina and X. dendrorhous resulted in a significant enhancement of total carotenoid accumulation within the co-culture (569 μg/g of dry biomass). The same medium, also, increased biomass of N. salina (0.24 ± 0.01 g/L vs. 0.11 ± 0.02 g/L in f/2 alone). Antioxidant activity also improved in microalgal biomass. Although X. dendrorhous biomass decreased slightly (1.51 ± 0.05 g/L vs. 1.79 ± 0.11 g/L in PE), its total lipid content increased significantly (30.2 ± 1.43 mg/L vs. 16.7 ± 1.43 mg/L), with implications for volumetric productivity. These findings demonstrate the potential of co-culturing microbial species of industrial interest in low-cost composite media for sustainable production of lipids and antioxidants with potential applications in functional foods and agricultural formulations.