Iron-Regulated Lysis of Recombinant Escherichia coli in Host Releases Protective Antigen and Confers Biological Containment

Abstract

ABSTRACTThe use of a recombinant bacterial vector vaccine is an attractive vaccination strategy to induce an immune response to a carried protective antigen. The superiorities of live bacterial vectors include mimicry of a natural infection, intrinsic adjuvant properties, and the potential for administration by mucosal routes.Escherichia coliis a simple and efficient vector system for production of exogenous proteins. In addition, many strains are nonpathogenic and avirulent, making it a good candidate for use in recombinant vaccine design. In this study, we screened 23 different iron-regulated promoters in anE. coliBL21(DE3) vector and found one, PviuB, with characteristics suitable for our use. We fused PviuBwith lysis geneE, establishing anin vivoinducible lysis circuit. The resultingin vivolysis circuit was introduced into a strain also carrying an IPTG (isopropyl-β-d-thiogalactopyranoside)-inducible PT7-controlled protein synthesis circuit, forming a novelE. coli-based protein delivery system. The recombinantE. coliproduced a large amount of antigenin vitroand could deliver the antigen into zebrafish after vaccination via injection. The strain subsequently lysed in response to the iron-limiting signalin vivo, implementing antigen release and biological containment. ThegapAgene, encoding the protective antigen GAPDH (glyceraldehyde-3-phosphate dehydrogenase) from the fish pathogenAeromonas hydrophilaLSA34, was introduced into theE. coli-based protein delivery system, and the resultant recombinant vector vaccine was evaluated in turbot (Scophtalmus maximus). Over 80% of the vaccinated fish survived challenge withA. hydrophilaLSA34, suggesting that theE. coli-based antigen delivery system has great potential in bacterial vector vaccine applications.