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

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 KLa, 0.11 s−1, values.

► In this study, pH operation strategy was developed for rHuEPO production by P. pastoris.
► Four phase operation was conducted to obtain higher product amount.
► Sorbitol batch/methanol fed-batch feeding was applied in production step.
► At pH ≥ 5.0 same cell growth profiles were obtained in the first two phases of the operation.
► In the production phase, the highest cell and rHuEPO concentration was obtained at pH = 4.5.