Optimization of the Physiochemical Parameters for the Culture of Bombyx Mori Insect Cells Used in Recombinant Protein Production

Silkworm (Bombyx mori, Bm5) cell growth at different environmental conditions was systematically studied in controlled bioreactors. The physiochemical parameters, which affect the growth of Bm5 cells, were defined and optimized. The growth rate was maximal at a medium osmolality of about 370 mosm kg-1; and more than 90% of the maximum growth rate was achieved with osmolality between 350 and 385 mosm kg-1. The optimum pH for Bm5 cell growth was from 6.10 to 6.30. Moreover, the effect of dissolved oxygen concentrations (higher than 20% air saturation) on growth was minimal. However, the maximum cell density decreased markedly with dissolved oxygen tensions less than 20%. The shear protection additive Pluronic F-68 had a very important effect on the growth of Bm5 cells in bioreactors with an optimum concentration of 0.2% (w/v). Compared to the original culture condition, the optimized conditions resulted in a twofold increase in cell yield and a reduced population doubling time from 48 to 36 h. Furthermore, the yield of a recombinant protein (CAT) was increased substantially in the optimized cultures.