Fed-batch cultivation of Arthrospira (Spirulina) platensis: potassium nitrate and ammonium chloride as simultaneous nitrogen sources

Arthrospira platensis was cultivated in minitanks at 13 klux, using a mixture of KNO3 and NH4Cl as nitrogen source. Fed-batch daily supply of NH4Cl at exponentially-increasing feeding rate allowed preventing ammonia toxicity and nitrogen deficiency, providing higher maximum cell concentration (Xm) and high-quality biomass (21.85 mg chlorophyll g-1 cells; 20.5% lipids; 49.8% proteins). A central composite design combined to response surface methodology was utilized to determine the relationships between responses (Xm, cell productivity and nitrogen-to-cell conversion factor) and independent variables (KNO3 and NH4Cl concentrations). Under optimum conditions (15.5 mM KNO3; 14.1 mM NH4Cl), Xm was 4327 mg L-1, a value almost coincident with that obtained with only 25.4 mM KNO3, but more than twice that obtained with 21.5 mM NH4Cl. A 30%-reduction of culture medium cost can be estimated when compared to KNO3-batch runs, thus behaving as a cheap alternative for the commercial production of this cyanobacterium