bioreactor studies of heterologous protein production by ...

eported reduced stabiliity in the stationary phase. Growth rate iu the stationq phase is
usualiy mhimai, and effm of specific pwth rate on plasmid stability have ken
examined as discussed in later sections of this review.
Manipulating the ploidy of the host ceil ako has an effect on plasmid stability. For
the higNy unstable, ARS-based plasmid YRp7M. a signifiant increase in segregational
stability was observed with increasing ploidy, whüe the nlatively stable. 2 jhn based
plasmid pMA3a showed oniy a slight increase in stability in saains of higher ploidy
(Splalding et ai., 1989). Greater plasrnid stabiiity in diploids was reported also by Mead et
al. (1986). Industrial yeast strains for brewing and baking are usualiy polyploid
Attempts to improve plasmid stability have focused mainly on rnanipuiating the
plasmid; littie attention has been paid to the genetic constitution or the physiological state
of the host. Manipulahg host ceiis is certainly an option for irnproving piasrnid stabiiity.
Much work rrrrnains to be done in this area
2.22. Environmental Factors
CelI's response to the environment onginates ultunately at the genetic level; hence, the
cuitme conditions profoundly affkct piasmid Stability and expression (Table 2.2). Control
and manipulation of the environment are particularly relevant to large scale culture where
the feasîbiiity of production depends on the cost of providing the reqwsife environment
Moreover, once a suitably engineered host is selected for production, environmentai