High cell density cultivation of Escherichia coli is widely used for the production of recombinant proteins. Product yield is thereby dependent on cell density and also on cell specific productivity. Therefore, a lot of research and development work has been dedicated to high cell density fermentations (Lee and Blanch, 1992; Riesenberg and Guthke, 1999). Most of the research work on the production of recombinant proteins focuses on E. coli due to well-known genetics and physiology.
The main problems arising from high cell densities are high oxygen and substrate uptake rates and accumulation of low molecular, growth inhibiting metabolites in the cell suspension during the cultivation. To minimise the formation of inhibitors, providing optimal growth conditions is essential.