An air-pressurized culture was used to enhance the oxygen transfer rate in the high cell density cultivation (HCDC) of non-recombinant and recombinant (harbors pBR322trpAB) Escherichia coli K-12. Carbon dioxide generated by the cells under increased pressure was inhibitory and as a result, cellular growth stopped in the air-pressurized culture at a constant mass flow rate. Increasing the flow rate along with the pressure in the reactor enabled the cells to grow to 130 (non-recombinant) and 104 (recombinant) g/l due to the release of the CO2. In addition, the specific activity of tryptophan synthase was increased. This study showed that an air-pressurized culture is able to meet the high demand for oxygen in the HCDC of E. coli. (c) 2005 Elsevier Ltd. All rights reserved.