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 mM 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.