Abstract: An Escherichia coli bacterial strain contains a gene encoding a recombinant protein and an open reading frame of i) a DNA fragment encoding an N-terminal signal peptide which mediates translocation of the protein into the periplasm, wherein the N-terminal signal peptide is an amino acid sequence with at least 80% correspondence in relation to SEQ ID No. 2 from amino acids 1 to 20 or is a signal peptide of lipoproteins Pal, NlpI, NlpB or OsmB of Escherichia coli, linked to ii) a following DNA sequence (lpp(N)) encoding a lipoprotein (Lpp(N)) which, compared to SEQ ID No. 2 from amino acids 21 to 78, is a different in at most ten amino acids and iii) a further DNA sequence (lpp(C)) encoding a lipoprotein (Lpp(C)) which, compared to SEQ ID No. 2 from amino acids 21 to 78, is a different in at most ten amino acids.

Abstract: The invention relates to a fed-batch fermentation process which uses special E. coli host/vector systems for the purpose of efficiently forming recombinant proteins, in particular recombinant antibody molecules, preferably antibody fragments such as miniantibodies. Under the given conditions, the E. coli cells are able to grow at a maximum specific growth rate up to very high cell densities. After the recombinant product formation has been switched on, it is only the formed product which restricts growth; there is no growth restriction due to substrates or metabolic by-products. High space-time yields of recombinant proteins can be achieved in this manner.