Optimization of culture medium and photosynthetic characteristics of platymonas subcordiformis

Uniform design method was applied for culture medium optimization of a marine microalga, Platymonas subcordiformis. Using the uniform design table U₁₀*(10⁸), three key medium ingredients (nitrate-N, phosphate-P, and Tris-HAc buffer) were chosen as optimizing factors. Their effects on the pH variation, photochemical activity of photosystem II (PSII) and light harvesting pigment of microalga cultures were examined. The optimum medium ingredients were obtained as follows: NO₃^--N 9.5 mmol/L, PO₄^3--P 0.34 mmol/L, Tris-HAc buffer 6.7 mmol/L, under which P. subcordiformis cells could grow efficiently, reaching a density of (8.28±0.51) × l0⁶ mL^-1 within 15 d. It was found that the buffer Tris-HAc maintained a stable pH value, and high NO₃^--N level improved the photosynthetic efficiency and growth rate of cells.