Expression of foreign proteins in a Vibrio cholerae vaccine strain using the stationary phase hemagglutinin/protease promoter

The use of the hemagglutinin(HA)/protease promoter and secretion signals to drive expression and secretion of a foreign antigen in a live genetically attenuated cholera vaccine candidate is demonstrated. A Vibrio cholerae vaccine strain, containing a HA/protease-tetanus toxin C fragment (TCF) fusion, produced soluble-and cell-associated TCF. The fraction of TCF secreted to the culture medium was degraded unless expressed in a HA/protease-defective vaccine strain. Comparison of the hapA promoter with the strong Tac promoter using quantitative real time PCR revealed that at least five times more TCF mRNA was produced when expressed from the hapA promoter.