Abstract

The goal of this study was to determine the effect of urea on the growth and accumulation of commercially important metabolites (lipids, proteins, fatty acids and phycoerythrin) and antioxidant activity in the red microalga of commercial interest Porphyridium purpureum. One-litre cultures were established containing 140 mg N l(-1) or 400 mg N l(-1), using nitrate (potassium nitrate) or urea as nitrogen source. Urea was as suitable as nitrate as the nitrogen source for P. purpureum. The nitrogen source significantly affected lipid but not protein content in P. purpureum, whereas nitrogen concentration significantly affected protein and lipid content, with the highest values obtained under 30 mM potassium nitrate and 14.8 mM urea (= 400 mg N l(-1)). Phycoerythrin content was not affected by nitrogen source or concentration in the culture. Considering the economic convenience of urea as a nitrogen source, the strain was scaled-up outdoors in Concepcion, Chile (Mediterranean climate), in a closed tubular photobioreactor and an open raceway pond (350 and 700 litres, respectively) with 14.8 mM urea. Biomass production was about four times lower in outdoor systems than in 1-litre cultures; however, results were comparable to other large-scale trials. These results demonstrate the feasibility of using urea as a low-cost nitrogen source for P. purpureum culture and the viability of growing this species outdoors in Central-Southern Chile, where climate conditions are not traditionally considered suitable for setting up commercial microalgal cultures.