Statistical optimization of culture media for production of phycobiliprotein by Synechocystis sp. PCC 6701

Synechocystis sp. PCC 6701 has a brilliantly colored pigment, phycobiliprotein containing phycoerythrin. Culture medium was optimized by sequential designs in order to maximize phycobiliprotein production. The observed fresh weights after 6 days were 0.58 g/L in BG-11, 0.83 g/L in medium for Scenedesmus sp. and 0.03-0.52 g/L in the other tested media. Medium for Scenedesmus sp. was selected to be optimized by fractional factorial design and central composite design since the medium maintained a more stable pH within a desirable range due to higher contents of phosphate. The fractional factorial design had seven factors with two levels: KNO₃, NaNO₃, NaH₂PO₄, Na₂HPO₄, Ca(NO₃)₂, FeEDTA, and MgSO₄. From the result of fractional factorial design, nitrate and phosphate were identified as significant factors. A central composite design was then applied with four variables at five levels each: nitrate, phosphate, pH, and light intensity. Parameters such as fresh weight and phycobiliprotein contents were used to determine the optimum value of the four variables. The proposed optimum media contains 0.88 g/L of nitrate, 0.32 g/L of phosphate under 25 μE·m^-2 ·s^-1 of light intensity. The maximum phycobiliprotein contents have been increased over 400%, from 4.9 to 25.9 mg/L after optimization.