NaCl stress mediated lipid and carotenoid production in freshwater microalga Kirchneriella obesa by optimization of medium composition using response surface methodology

Abstract Optimal nitrate, phosphate and salinity for maximal biomass, lipid and carotenoid content of the freshwater microalga Kirchneriella obesa were investigated by using Box-Behnken Design. In an optimised condition, these three factors enhanced biomass production by 0.64 g/L more than the control (0.25 g/L). At 2.5 g/L nitrate, 0.04 g/L phosphate, and 25 mM NaCl, the maximum lipid accumulation (46.02%) and carotenoid content (2.58 mg/L) were achieved. The fit of the model yielded R2 values of up to 0.9955 for biomass, 0.9984 for lipids and 0.9999 for carotenoid, respectively. For the highest carbohydrate (418.28 mg/L) content, the medium was supplemented with 1.5 g/L nitrate, 0.04 g/L phosphate, and 40 mM NaCl. While the highest protein content (320.53 mg/L) was attributed to the medium with 3 g/L nitrate, 0.02 g/L phosphate and 25 mM NaCl. The major fatty acid compositions found in this algae were C18:1trans (16.36 ± 1.4), C18:1cis (6.001 ± 0.44), C18:2 (8.32 ± 1.1) and C18:3 (34.39 ± 2.3%), demonstrating their importance in biofuel production and human health.