Dissolved carbon dioxide accumulation in a large scale and high density production of TGF beta receptor with baculovirus infected Sf-9 cells

Production of a TGF beta receptor with high density baculovirus infected Sf-9 cells (7 x 10(6) cells ml(-1)) served as a test run for a retrofitted 150 L microbial fermenter. The entire 110 L batch run was performed in serum free medium, with an addition of a concentrated amino acid and yeastolate mixture at the time of infection. This addition strategy has been proven effective at a small scale by enabling cultures to maintain maximum product yield. In the bioreactor however, while cellular growth was comparable to that of the smaller scale control, TGF beta receptor production was three fold below the control. To minimize the mechanical stress, low flow rate of pure oxygen was used to control the dissolved oxygen at 40%. As a consequence, it seems that this aeration strategy involved an accumulation of dissolved carbon dioxide that in turn inhibited the protein production. A model has been developed that estimated the CO2 partial pressure in the culture to be in the vicinity of 0.15 arm. The effect of dissolved CO2 at this concentration has been assessed at smaller scale for TGF beta receptor and beta-gal expression, in controlled atmosphere incubators.