Parallel substrate feeding and pH-control in shaking-flasks.

An intermittent feeding system for shaking-flasks was developed to close the gap between batch operated shaking-flasks and fed-batch operated as well as pH-controlled stirred tank reactors. A precise syringe pump was connected via a substrate distribution system to individual 2/2-way miniature valves, one for each of up to 16 shaking-flask. The shaking-flasks were equipped with pH-probes. A process computer controls the intermittent feeding of substrates by tracking predefined individual feeding profiles as well as the base (or acid) addition for individual pH-control of the shaking-flasks. Higher concentrations of aerobic cells with higher cellular activities were achieved in fed-batch operated and pH-controlled shaking-flasks as compared to the conventional batch operation. Physiological effects of an intermittent feeding were studied in a stirred tank reactor with a recombinant E. coli strain, which expressed the GDP-mannose-pyrophosphorylase enzyme under the control of the lac-promoter.