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 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(L)a, 0.11 s(-1), values