bioreactor studies of heterologous protein production by ...

+ s
Dilution Rate = p' = CI,- -
K*+S '
however. plasmid-free ce& do not grow, or grow very slowly, because of the seledon
pressure. Thenfore. the growth ratio (a = p-/p+) decreases as the dilution rate is
increased, so the plasmid is more stable* III the case of nonseleztive media. because the
growth rate of recombinants is addy âffected by the borden of plasmids and the
expression of recombinant DNA (Moo-Young et aL, 1996). piasmici-fke ce& iisually
have a growth advanrage. In general, the growth ratio (a) exceeds unity, ranging over 1.0
to 2.0 (hanaka and Aiba, 198 1). Increaring dilution rate in nonselective media even cm
Mer raise the growth ratio (a) becaw the plasmid-behg cells are less able to respond
to the dilution rate changes Therefore. it is not surprising that plasmid stability decreases
with increasing dilution rate in the nonseleaive media In fact, in continuous culture of
recombinant cells, it is impossible to achieve steady state in nonselective media if the
growth ratio (a) is more than 1. The initial plasruid-bearing ceii population is sure to be
taken over by the plasmid-£ree ceik eventuaily.
222.5. Bioreactor Operation Modes
Fermentation pmcesses are usuaIly openited as batch, fed-biitch, or continnous cdtore.
The modes of operation cm infiuenœ the plasmid stability and the productivity of
expressed products. In batch culture, plasmids are nlatively stable because the culture
periods are generally short, hence, the nomber of generations since inoculation is maiL
Because of long growth periods. conthrious culture of recombinant cells suffers hm