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

Optimizing nutrient formulations is essential to improving the biomass yield and C-phycocyanin (C-PC) productivity of <i>Spirulina</i> sp., a cyanobacterium with wide-ranging applications in food, pharmaceutical, and biotechnological industries. This study evaluated the effects of macronutrient modifications on growth and pigment biosynthesis using a two-level full factorial design across eight Zarrouk-based formulations compared to the standard medium. Cultivation experiments were conducted in triplicate, and growth was evaluated using linear growth rate, maximum optical density (OD₆₈₀), and dry biomass, while C-PC was quantified in crude extracts (PCL), dried biomass (PCD), and the purity index (PI). Among the tested formulations, F2 (16 g/L NaHCO₃, 5 g/L NaNO₃, 0.25 g/L K₂HPO₄) achieved the highest biomass productivity, yielding a 37.6% increase in dry weight and a 38.1% improvement in daily productivity compared to the control. In contrast, F3 (16 g/L NaHCO₃, 5 g/L NaNO₃, 1 g/L K₂HPO₄) yielded the highest C-PC content, nearly doubling both PCL and PCD values and enhancing pigment purity by 40.2%. ANOVA and interaction analyses confirmed that carbon and nitrogen synergistically promoted biomass formation, while phosphorus had a strong effect on pigment biosynthesis through C:N:P interactions. These findings demonstrate that <i>Spirulina</i> sp. requires distinct nutrient balances for optimal growth and pigment formation. Formulation F2 is ideal for maximizing biomass productivity, whereas F3 is optimal for high-value C-PC production. The results provide a rational framework for designing nutrient-efficient cultivation systems to advance sustainable <i>Spirulina</i>-based biomanufacturing.