Enhanced recombinant human erythropoietin production by Pichia pastoris in methanol fed-batch/sorbitol batch fermentation through pH optimization

Abstract

The effects of pH on recombinant human erythropoietin (rHuEPO) production by Pichia pastoris was investigated at pH = 4.0, 4.5, 5.0, 5.5 and 6.0, where sorbitol and methanol were supplied to the bioreactor in batch and fed-batch mode, respectively, in the recombinant protein production phase (PP). For the first three phases, glycerol batch (GB), glycerol fed-batch (GFB) and methanol transition (MT), the growth profiles were almost the same for pH ≥ 5.0; however, at pH < 5.0 the growth rate was lower. The highest cell concentration was obtained as 81.4 g L −1 where GB and GFB were operated at pH = 5.0 and MT and PP were operated at pH = 4.5. Sorbitol added at the beginning of PP, was totally consumed within 15 h, at pH ≤ 5.0; however, at pH > 5.0 sorbitol consumption rate decreased. The highest rHuEPO concentration was achieved at pH = 4.5 as 0.16 g L −1, where the overall cell and rHuEPO yield on substrate, were 0.5 g g −1 and 1.5 mg g −1. pH did not have a significant effect on extracellular protease activity. The highest specific AOX activity (110 U g −1 CDW) was attained at pH = 4.5 parallel to the highest rHuEPO production. At pH = 4.5, higher oxygen demand of the cells resulted in higher oxygen K La, 0.11 s −1, values.