BATCH AND FED-BATCH CULTURES OF ESCHERICHIA-COLI TB1 AT DIFFERENT OXYGEN-TRANSFER RATES - EFFECT OF STIRRING AND OXYGEN PARTIAL PRESSURES ON CELL-GROWTH AND CYTOCHROME B5 PRODUCTION

Batch cultures off. coli TB1/pUC13 were carried out at different oxyge n transfer rates (OTR) enhanced by the increase of stirring rate and b y the increase of air total pressure of the bioreactor. These two vari ables showed to have little effect on cell growth but a negative effec t on cytochrome b5 (recombinant protein) production. However, this eff ect was more significant of high stirring rates than for values of pre ssure up to 0.4 MPa. The effects of stirring and pressure were also in vestigated for fed-batch mode operation. In this type of cell cultivat ion high cell densities are reached, thus a high capacity of oxygen su pply of the system is required. To compare the two ways of improving O TR, cell behaviour was followed in two bioreactors at different operat ional conditions giving the same maximum OTR value. The first one oper ated at a high stirring rate (500 rpm) and at atmospheric pressure (0. 1 MPa) and the other one at high air pressure (0.48 MPa) and low stirr ing rate. The increased pressure seemed to be a better way of ensuring an adequate oxygen supply to a culture of E. coli TB1 cells than an i ncreased stirring rate. For the high pressure experiment a higher cell ular density was reached, as well as a higher cyt.b5 expression which led to a 4-fold increase in final productivity. These experiments show ed that bioreactor pressurization can be successfully used as a means of enhancing oxygen mass transfer to shear sensitive cell cultures.