bioreactor studies of heterologous protein production by ...

On the other hand, the decay kinetics for enzyme production can be described by
Equation (5.26b). Since the pmbability of plasmid los @) is maiiy srnaii, Equation
(5.26b) may be simpMed as the following:
p = exp(-pW = P, exp(7,t) (5.28)
wherey,is a fint-order decay rate constant for enzyme production. Equation (5.28)
shows that iike the concentration of plasmid-bearing cells, the decay of enzyme
concentration &O follows tint-onier kinetics. From Equations (5.24b) and (5.28), it is
interesthg to note that, theoretically, the enzyme concentration decay rate constant (v) is
the same as the plasmid los constant ( kf) at a fixed dilution rate, that is:
y, =k, =PD
h order to test the pmposed models for the plasmid los and enzyme production
decay kinetics, continuou suspension cultures were perfomed in the airiift bioreactor at
different dilution rates. As shown in Figure 5.8. both plasmid-karing celi and enzyme
concentration followed an exponentiai decay pattern, which agrees well with Equations
(5.24b) ana (5.28). Apparent hm-order decay constants for dinerent dilution rates are
üsted in Table 5.3. As shown in Table 5.3, the apparent kinetic constants for plasmid loss
and enzyme pmdutim decay decreved with hcreasing dilution rate. The results are
consistent with Equation (5.29); the fim-order üecay constants are expected to be directiy
proportional to the dilution rate. The probabiiity of plasmid loss (p) due to structurai
instability andfor segregational instability is an important parameter in studying recombi-