Objective The effects of nitrogen, phosphorus, carbon and iron nutrients on the growth of Oocystis borgei were explored, and the optimal nutrient formula was selected to provide references for its efficient and large-scale cultivation.

Method Single factor test was used to analyze the effects of different nitrogen, phosphorus, carbon and iron nutrients on the growth of O. borgei, to obtain the best nutrients and their respective concentrations. Orthogonal tests were conducted to optimize the factors that had a great impact on the the growth of O. borgei. Finally, the optimal nutrient formula was obtained.

Result The results of the single factor test showed that the optimal sources and concentrations of nitrogen, phosphorus, carbon and iron sources for O. borgei were CO(NH₂)₂ 160 mg/L, C₃H₇Na₂O₆P 8 mg/L, NaHCO₃ 1 g/L, and FeCl₃ 0.2 mg/L, respectively. The results of the orthogonal tests showed that the effect of each nutrient on the growth of O. borgei ranked as: phosphorus source > nitrogen source > carbon source, and phosphorus source had the most significant effect on the growth of O. borgei (P < 0.05). The optimal formula was: CO(NH₂)₂ 120 mg/L, C₃H₇Na₂O₆P 12 mg/L and NaHCO₃ 2.5 g/L. Under the optimal condition, the algal cell density reached 22.07×10⁶ cells/mL, which was 12 times higher than that before optimization (1.74×10⁶ cells/mL).

Conclusion The optimal nitrogen, phosphorus, carbon, and iron sources and concentrations for O. borgei were determined and the optimal nutrient formula was obtained by optimizing the conditions, which significantly increased the algal cell density.