High cell density fermentation of recombinant Vibrio cholerae for the production of B subunit of Escherichia coli enterotoxin

High cell density fermentation studies were performed to produce the B subunit of Escherichia coli heat‐labile enterotoxin (LTB) from a Vibrio cholerae culture that carries a recombinant plasmid with an ampicillin resistance gene, tac promoter, and the gene encoding LTB. Upon induction with isopropyl‐β‐ D ‐thiogalactopyranoside (IPTG) the culture secreted the protein into the extracellular milieu. Fed‐batch fermentation with stepwise addition of a total of 5 m M of IPTG during the active growth phase of the organism resulted in the production of 400 mg/L of LTB in 9 h and a cell optical density (OD) of 24. The LTB was purified to homogeneity with 70% recovery from the fermentation broth and was found to be chemically and biologically identical to the native protein by N ‐terminal amino acid sequencing and receptor binding assay. © 1995 John Wiley & Sons, Inc.