重组巴斯德毕赤酵母高密度培养中铵离子浓度的影响

采用Mut^s表型的重组毕赤酵母生产血管生长抑制素，表达阶段流加甘油—甲醇混合碳源以提高菌体密度和血管生长抑制素的表达水平，菌体密度可达174g／L，约是表达阶段采用甲醇为单一碳源的发酵过程的3倍。菌体密度的提高导致表达阶段发酵液中铵离子浓度下降很快，当发酵液中的铵离子浓度低至40mmol／L时，影响了血管生长抑制素的表达。改变pH调节方式并在发酵后期添加25mmol／L(NH4)2SO4使发酵液中铵离子浓度维持在150mmol／L以上，血管生长抑制素的表达产量达到108mg／L。

Effect of Ammonium Concentration on the Expression of Angiostatin in High Cell Density Culture of Recombinant Pichia pastoris

In fed-batch cultivation of recombinant Pichia pastoris (Mut~S phenotype), feeding with glycerol and methanol was conducted during the expression phase to enhance the cell growth and angiostatin expression. The cell density reached 174 g/L at the end of fermentation, which was about 3 fold of that obtained with methanol as the sole carbon source in the induction phase. High cell density resulted in a quick drop of ammonium concentration in the fermentation broth, and when the ammonium concentration was below 40 mmol/L, the production of angiostatin also decreased. The change of pH control strategy and addition of 25 mmol/L (NH_4)_2SO_4 were applied to release the effect caused by low ammonium concentration. The ammonium concentration was maintained above 150 mmol/L in the induction phase, and 108 mg/L angiostatin was achieved at the end of fermentation.