High cell density fermentation of recombinant Escherichia coli expressing human interferon alpha 1

Summary A defined medium was developed which, by means of a specific fed-batch mode, allows growth of the recombinant Escherichia coli strain TG1 (pBB210) up to a cell density of 60 g dry weight/l. Apart from glucose and aqueous ammonia fed as carbon and nitrogen sources, it was unnecessary to supply other nutrients or O₂-enriched air. Aqueous ammonia also served for pH control. The pO₂ level was kept at 20% saturation via closed-loop controls operating the two output variables of stirrer speed and glucose feeding rate. This fed-batch method prevented significant accumulation of acetate and other metabolic by-products. The recombinant E. coli expressed interferon alpha 1 more efficiently at a lower specific growth rate (_Pr 0.15 h^–1) than at the maximum specific growth rate (_max = 0.45 h^–1). Therefore, fermentation in the batch phase at _max was only allowed to continue up to a medium cell density. In the succeeding fed-batch phase, the specific growth rate was reduced to _Pr by increasing the stirrer speed according to an empirically developed time scale. Offprint requests to: D. Riesenberg