Effect of pH value and dissolved oxygen concentration on expression of hepatitis B surface antigen by genetically engineered yeast in fermentation processes.

Both cell growth and expression of hepatitis B surface antigen (HBsAg) interact with each other in fermentation to produce exogenous protein HBsAg by genetically engineered yeast, S. cerevisiae, which contains the HBsAg gene. Since both processes required proper pH values in order to improve the overall yield, a suitable pH value sequence was determined. It is important that dissolved oxygen concentration in fermentation should be controlled to maintain the stability of recombinant plasmids and to obtain the high HBsAg expression. When the concentration of dissolved oxygen was controlled at 70% saturation, the stability of recombinant plasmid was maintained at 73%, and the relative concentration of HBsAg expression was found to be 98.6.