title: Kinetics and stability of GM-CSF production by recombinant yeast cells immobilized in a fibrous-bed bioreactor.
abstract: The continuous production of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) by recombinant yeast cells immobilized in a fibrous-bed bioreactor was studied. A high cell density of approximately 68 g/L and a GM-CSF productivity of approximately 3.5 mg/L.h were attained in the fibrous-bed bioreactor-fed with a rich (nonselective, pH 6.7) medium at a dilution rate of 0.16 h-1. The GM-CSF production was stable even though the fraction of plasmid-carrying cells in the reactor effluent gradually dropped below 5% over a period of 2 weeks. At the end of that period, the immobilized cells in the fibrous matrix still had a high fraction, approximately 26%, of plasmid-carrying cells. Similar results were obtained with reactors operated at 0.05 h-1 dilution rate and pH 4.0. Although the GM-CSF production was lower at pH 4, the reactor was stably operated for over 4 weeks without contamination or significant loss of productivity. The stable long-term GM-CSF production from the fibrous-bed bioreactor was attributed to the effect of cell immobilization on plasmid stability. Because GM-CSF production was growth-associated, as was found in batch fermentation with free cells, this stabilization effect cannot be attributed solely to the reduced cell growth in the immobilized cell environment. Plasmid-carrying cells were preferentially retained in the fibrous matrix, perhaps because their abilities to adhere to the fiber surface and to form cell aggregates were higher than those of plasmid-free cells.
authors.affiliation: Department of Chemical Engineering, Ohio State University, Columbus 43210, USA. yangst.15@osu.edu
authors.forename: S T
authors.initials: ST
authors.lastname: Yang
authors.forename: C H
authors.initials: CH
authors.lastname: Shu
mesh_terms: D000818:Animals; D018914:Cells, Immobilized; D003115:Colony-Stimulating Factors / Q000096:biosynthesis*; D003470:Culture Media; D000431:Ethanol / Q000737:chemistry / Q000378:metabolism; D005285:Fermentation; D005947:Glucose / Q000737:chemistry / Q000378:metabolism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000096:biosynthesis*; D007700:Kinetics; D051379:Mice; D008855:Microscopy, Electron, Scanning; D010957:Plasmids / Q000235:genetics; D011994:Recombinant Proteins; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D003115:Colony-Stimulating Factors; D003470:Culture Media; D011994:Recombinant Proteins; D000431:Ethanol; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D005947:Glucose