bioreactor studies of heterologous protein production by ...

period the ce& &~g glucose as carbon source, grew rapidly in the first exponential
phase. After about 12 hours, the glucose was completely consumed and ethanol reached a
maximum concentration. Then the ce& began to utiiize ethanol as carbon source and
another exponential growth foIIowed. Total tell concentration achieved a maximum value
after about 36 hours and then rernained constant in a stationary phase due to the
exhaustion of ethanol. The total ceii concentration included both pIasmid-karing and
plasmid-free cens. Glucoamylase concentration increased with inmashg cell
concentration during the two exponential growth phases, reiilching its maximum when cd
growth approached stationary phase. This suggested that giucoamylase secretion was
gmwth-associated-
Plasrnid stability was &O examined during batch culnue by foiIowing the fraction
of plasmid-bearing cells. Figure 4.1 shows that the fiaction of plasmid-behg cells
decreased with culture tirne. indicating that plasmid loss occumd during the batch culture.
Figure 4.1 also shows that the fraction ûf plasmid-bearing ceils feu more rapidly duMg the
first growth phase on glucose than duMg the second growth phase on ethano1. This is
because the specific growth rate in the nrst exponential growth phase was higher than that
in the second exponential phase. The more the ceiI divided, the more EkeIy they lost
plasmids. It appears that the segregational instability maidy contributed to plasmid loss.