| Two continuous multiphase bioreactors, a draft-tube fluidized bed and a novel spiral wound fibrous bed, were studied for the production of a recombinant murine granulocyte-macrophage colony-stimulating factor (MuGM-CSF) by immobilized recombinant yeast cells. The recombinant cells, Saccharomyces cerevisiae strain XV2181, contained the expressin vector p;GM-CSF production was found to be growth-associated in batch fermentations with ethanol as the carbon source at pH 4.0 and 6.0. As pH increased, the final fraction of plasmid-carrying cells increased from 50% to 70%, and the specific production also increased from 6.24 to 13.30 mg P/g X. Besides, a high pH favored product yield, productivity, and specific productivity.;In continuous fermentation with free cells, plasmid stability was growth rate (dilution rate) dependent, as was product yield, productivity, and specific productivity. As the dilution rate increased from 0.05 to 0.11 hr;In fermentations with the fluidized bed bioreactor, as solid loading increased, plasmid stability increased, as did the productivity, product yield, and total cell density in the bioreactor. In contrary, the cell yield, specific productivity, and cell density per gram of beads decreased. A mathematical model was proposed and used to evaluate plasmid stability and specific growth rate of the immobilized recombinant cells. Model simulation showed that the low specific productivity obtained at high solid loading was caused by the low growth rate of immobilized cells.;The feasibility of using a novel spiral wound fibrous bed bioreactor for recombinant yeast fermentation was also demonstrated in this study. Experimental results indicated that the proposed spiral bed bioreactor would provide a high cell density (... |
