Abstract
Recombinant protein production in microorganisms is one of the most studied areas of research in biotechnology today. In this respect the yeast Pichia pastoris is an important microbial production host due to its capability of secreting the target protein and performing posttranslational modifications. In a recent study, we described the development of a robust bioprocess for a glyco-engineered recombinant P. pastoris strain where the native α-1,6-mannosyltransfrease OCH1 was knocked out (Δoch1 strain). This strain produced the glycosylated enzyme horseradish peroxidase (HRP) with more homogeneous and shorter surface glycans than the respective benchmark strain. However, the recombinant Δoch1 strain was physiologically impaired and thus hard to cultivate. We faced cell cluster formation, cell lysis and consequent intensive foam formation. Thus, we investigated the effects of the 3 process parameters temperature, pH and dissolved oxygen concentration on (1) cell physiology, (2) cell morphology, (3) cell lysis, (4) productivity and (5) product purity in a multivariate manner. However, not only process parameters might influence these characteristics, but also media supplements might have an impact. Here, we describe the effects of different heme-precursors as well as of a protease-inhibitor cocktail on the production of active HRP in therecombinant P. pastoris Δoch1strain.