A two-stage
bioreactor scheme was developed for the large-scale production of
recombinant proteins using a genetically engineered baculovirus/insect cell system. The first
bioreactor was employed for cell growth and the second for cell
infection. Silkworm Bm5 cells were infected with a recombinant baculovirus, BmNPV/P5.cat, containing a bacterial
chloramphenicol acetyltransferase (CAT) gene under the control of the polyhedrin gene promoter of Bombyx mori nuclear polyhedrosis virus (BmNPV). This recombinant baculovirus has been used as an expression vector for the production of recombinant
CAT enzyme. A specific productivity of 82 to 90 microg CAT/(10(6) cells) was obtained using the BmNPV/Bm5 expression system, a yield similar to that achieved using the AcNPV/Sf expression system. Repeated
infection of high-density cell cultures did not reduce the specific productivity of the
CAT enzyme. Most importantly, the problems associated with the
infection of high-density cell cultures were resolved by means of controlled
infection conditions and appropriate replenishment of spent culture medium following
infection. The
glucose uptake rate by the cells following
infection was 50% higher than that by the cells before
infection. Not only did the
infection of high-density cell cultures result in consistent yields of 250 mg/L of
CAT enzyme, but also the two-stage
bioreactor system was proven to be reliable for a long-term operation beyond 600 h.