bioreactor studies of heterologous protein production by ...

understanding of the nature of the immobiüÿed recombinant yeast through experiments
and modelling.
6.2. Continuous Culture in XmmobiIizeà-Ceil Bioreactor
62.1. Modd Development
An idealised modei is w d
to characten.ize the Unmobiliwl cell system as jiiustrated in
Figure 6.1. As shown in Figure 6.1, the i-d biofilm has a unifonn density of œUs
attached to the support and a locally d o m thickness with negiigible interna1 and
extemal mas W e r mistance. 'Ihese assurnptions may be justified for the present
immobïiized-ceU-film airM bioreactor because of the thin biofilm (les than 2.0 mm ) and
suong hydmdynamic Nculation and mixing in the bioreactor. It is ako assumed that no
growth merence between the plasrnid-bea~g and plasmid-frez cells ex&&, which was
confimied for the present ncombinant yeast in previous studies. Under these
assumptions, an identicai specific growth rate for both the biofïim and suspended plasmid-
bearing and plamid-Eree ceh in the immobilized-ceiî-fîim biore-r may be justified. The
specific growth rate of the immobilized ceil system at a fïxed dilution rate is denoted as
in the immobïiized-cetl-fi airlift bioreactor, ceils grow on the cloth film and are
continuously detached into the medium due to hydrodynamic forces. It is unlüUely that
additional free space wiU be avaiiable for re-entiy of the released œk onto the Wy-
covend cloth surface again (Ghose, 1988). huming a constant vaiue of plasmid los