Process for the preparation of recombinant proteins in E. coli by high cell density fermentation

A high density fermentation process for producing a foreign protein from E. coli cells which have been transforrned with a plasmid carrying an inducible promoter and, regulated by that promoter, a nucleic acid which encodes the protein, wherein there is no restriction of cell growth by substrates or metabolic by-products, comprising

• a) culturing the cells under batch fermentation conditions, then
• b) performing a fed-batch step, wherein the concentration of the carbon source in the medium is kept in a range from 0.1 g/l to 25 g/l while maintaining unlimited growth of the cells, and the pO2 is adjusted to between 5 and 25% by passing oxygen into the fermentation broth, which comprises
• i) inducing the promoter at a cell density of between 10 and 80 g/l, thereby initiating the production of the foreign protein, and then
• ii) continuously feeding in utilizable nitrogen, phosphate, and salts of trace elements.