Key Nutrient Drivers for Biomass and C-Phycocyanin Production in <em>Spirulina</em> sp. Revealed by Media Optimization

Optimizing nutrient formulations is crucial to enhancing the biomass and C-PC productivity of Spirulina sp., a promising cyanobacterium widely used in food, pharmaceutical, and biotechnological applications. This study aimed to identify key macronutrient drivers that influence biomass growth and C-PC productivity through cultivation media optimization. A two-level full factorial design was used to evaluate eight modified Zarrouk-based formulations compared to the standard medium. Among them, formulation F2 (16 g/L NaHCO₃, 5 g/L NaNO₃, 0.25 g/L K₂HPO₄) significantly improved biomass performance, with a 10.05% increase in specific growth rate, 37.25% higher dry biomass, and 37.5% greater daily productivity than the control. Meanwhile, formulation F3 (16 g/L NaHCO₃, 5 g/L NaNO₃, 1 g/L K₂HPO₄) achieved the highest C-PC content, doubling both PCL and PCD levels, and increasing purity index by 40.23% relative to the control. These findings reveal that nitrate and phosphate availability are critical nutrient drivers for enhancing Spirulina sp. productivity, offering a cost-effective strategy for maximizing both biomass yield and C-PC quality in commercial-scale cultivation.