bioreactor studies of heterologous protein production by ...

epeated batch fermentations, the femented culture was cornpletely separated h m the
yat nIm which was retained in the Uomobüized œii bioreactor at the end of each batch
fermentation. Evidentiy, the 6im retained nearly constant proportion of plasnid-bearing
cells. This proportion of plasrnid-bearing cells was equai to or higher than the proportion
in the liquid suspension. The free plasmid-bearing ceiis generated from the yeast film were
uniikely to lose plasmids due to the short culture penod. In continuou culture, however,
because of the longer culture penod. the fke cells continuously divided for many
genentions and tended to lose the plasrnids. Gnduaüy. the population of plasmid-free
celis increased with the culture Ume. causing lower recombinant pmtein production.
Use of the microbial tilms as mident inocula make it easy io opente repeated
batch fermentations in the proposed imrnobilized cell bioreactor. In commercial
fermentations, batch operation is usudiy preferred. Cienedy, a seed culture must be
prepared in 2 to 3 stages of increasing volume before starting a main batch fermentation.
A part of the old fermented culture may be used as an inoculum to repeat a batch
fennentation at the expense of a reduced product yield. But the fermented culture often
contains toxic substances which inhibit the growth of the microorganisms and the
production of the desired products. The hmested cells may be &O used to inoculate the
batch fermentation. However, harvest and readdition of cells nise the cost of
fermentation and increase the risk of contamination. Genetic instabüity could be another
senous problem associating with Uee suspension repeated fermentations. Lking the
proposed immobilized ce11 bioreactor cm overcorne di the above pmblems.