A Novel In Vivo Inducible Expression System In Edwardsiella Tarda For Potential Application In Bacterial Polyvalence Vaccine

Recombinant bacterial vector vaccine is an attractive vaccination strategy to induce the immune response to a carried protective antigen, and the main concern of bacterial vector vaccine is to establish a stable antigen expression system in vector bacteria. Edwardsiella tarda is an important facultative intracellular pathogen of both animals and humans, and its attenuated derivates are good bacterial vectors for use in recombinant vaccine design. In this study, we aimed to build an in vivo inducible expression system in E. tarda and establish potential recombinant E. tarda vector vaccine. With wild-type strain E. tarda EIB202 as a vector,53 different bacteria-originated promoters were examined for iron-responsive transcription in vitro, and the promoters Pdps and PyncE showed high transcription activity. These two promoters were further assayed for their transcription profile in vivo, and Pdps demonstrated an enhanced in vivo-inducible transcription in macrophage, zebrafish larvae and zebrafish adults. The gapA34 gene, encoding the protective antigen GAPDH from the fish pathogen Aeromonas hydrophila LSA34, was introduced into the Pdps-based protein expression system, and transformed into attenuated E. tarda strains. The resultant recombinant vector vaccine WED/pUTDgap was evaluated in turbot(Scophtalmus maximus). Over 60%of the vaccinated fish survived when challenging with A. hydrophila LSA34 and E. tarda EIB202, suggesting that the Pdps-based antigen delivery system had great potential in bacterial vector vaccine application.