bioreactor studies of heterologous protein production by ...

y Impoolsup et al. (1989b). Our hdings with the recombinant yeast are different h m
those found with recombinant E. di. For recombinant E. coli, it is weU-documented
that there is a difference in growth rates berneen plasmid-fke and pfasmid-bearhg ceils
(Seo and Baüey. 1985; Kim and Sholer. 1990b; Birnbam and Bailey, 1991; Flickingex and
Rouse, 1993). The disparity between recombinant yeast and recombinant E. coü may be
explained by the ciifference in piasmid copy number. For 2 pn based yeast episomal
plasmid (YEp). the copy number per ceii ranges frum 5 to 40 (Caunt et al., 1988). whik
recombinant E. d i
plasmids usually have much higher copy nurnbers (Seo and Bailey,
1985; Ryu and Lee. 1988; Kim and Shuler, 1990b; Topa et ai., 1993). The higher the
plasmid copy nurnber, the greater the additionai amount of energy required to maintain
that DNA within the host ceii, and consequently the lower the relative specific growth rate
(Kim and Shuler. 1990b; Birnbaum and Bailey, 1991). In addition, recombinant E. coli
generally has suonger promoters and a higher levei of cloned gene expression than S.
cerevisiae.
4 3 e 3 e S e Probability OP Plasrnid L m @)
In modelling plasmid instability, the probability of plasmid los (p) due to structurai
uistability and/or sepgationai instability is an important kinetic parameter. We have
show a new methodology to evaluate th& parameter (p). It cm be seen in Table 1 that
the probability of plasmid loss @) is nearly constant at aII dilution rates tested. So it can
concluded that the dilution rate has no signifiant effect on the plasmid stabiüty. This
6nding is conw to those found in a recombinant E. coli (Mosrati et al., 1993) and in