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

Abstract Arthrospira platensis was cultivated in minitanks at 13 klux, using a mixture of KNO 3 and NH 4 Cl as nitrogen source. Fed-batch daily supply of NH 4 Cl at exponentially-increasing feeding rate allowed preventing ammonia toxicity and nitrogen deficiency, providing high maximum cell concentration ( X m ) and high-quality biomass (21.85 mg chlorophyll g cells −1 ; 20.5% lipids; 49.8% proteins). A central composite design combined to response surface methodology was utilized to determine the relationships between responses ( X m , cell productivity and nitrogen-to-cell conversion factor) and independent variables (KNO 3 and NH 4 Cl concentrations). Under optimum conditions (15.5 mM KNO 3 ; 14.1 mM NH 4 Cl), X m was 4327 mg L −1 , a value almost coincident with that obtained with only 25.4 mM KNO 3 , but more than twice that obtained with 21.5 mM NH 4 Cl. A 30%-reduction of culture medium cost can be estimated when compared to KNO 3 -batch runs, thus behaving as a cheap alternative for the commercial production of this cyanobacterium