Evaluation of Arthrospira platensis extracellular polymeric substances production in photoautotrophic, heterotrophic and mixotrophic conditions

The kinetic study of Arthrospira platensis extracellular polymeric substances (EPS) production under different trophic modes-photoautotrophy (100 mu mol photons m(-2) s(-1)), heterotrophy (1.5 g/L glucose), and mixotrophy (100 mu mol photons m(-2) s(-1) and 1.5 g/L glucose)-was investigated. Under photoautotrophic and heterotrophic conditions, the maximum EPS production 219.61 +/- 4.73 and 30.30 +/- 1.97 mg/L, respectively, occurred during the stationary phase. Under a mixotrophic condition, the maximum EPS production (290.50 +/- 2.21 mg/L) was observed during the early stationary phase. The highest specific EPS productivity (433.62 mg/g per day) was obtained under a photoautotrophic culture. The lowest specific EPS productivity (38.33 mg/g per day) was observed for the heterotrophic culture. The effects of glucose concentration, light intensity, and their interaction in mixotrophic culture on A. platensis EPS production were evaluated by means of 32 factorial design and response surface methodology. This design was carried out with a glucose concentration of 0.5, 1.5, and 2.5 g/L and at light levels of 50, 100, and 150 mu mol photons m(-2) s(-1). Statistical analysis of the model demonstrated that EPS concentration and EPS yield were mainly influenced by glucose concentration and that conditions optimizing EPS concentration were dissimilar from those optimizing EPS yield. The highest maximum predicted EPS concentration (369.3 mg/L) was found at 150 mu mol photons m(-2) s(-1) light intensity and 2.4 g/L glucose concentration, while the highest maximum predicted EPS yield (364.3 mg/g) was recorded at 115 mu mol photons m(-2) s(-1) light intensity and 1.8 g/L glucose concentration.