Secretory expression of recombinant proteins in an attenuated Vibrio anguillarum strain for potential use in vaccines

Vibrio anguillarum is an important bacterial fish pathogen responsible for epizootics in both marine and freshwater fish worldwide. Studies on pathogenic V. anguillarum has shown that its virulence is mediated by a 65 kb endogenous pJM1-like plasmid, which encodes an efficient iron uptake system. The plasmid-free derivative of wild V. anguillarum was found to be greatly attenuated and elicited a good protection against wild V. anguillarum in fish. In this study, a plasmid-free derivative MVAV6201, an effective live vaccine candidate, was used as a carrier strain to achieve the secretory delivery of recombinant proteins in V. anguillarum. The secretion mechanism was based on the Escherichia coli alpha-haemolysin (HlyA) transport system. The recombinant proteins were fused with the alpha-haemolysin secretion signal (HlyAs) and expressed from the commonly used HlyA secretion vector pMOhly1. Two HlyAs-tagged recombinant proteins, GFP-HlyAs and AngE-HlyAs, were constructed and their secretion characters in V. anguillarum investigated. In the case of GFP-HlyAs, nearly 70% of the total fusion protein was efficiently secreted into culture supernatant, and in the case of AngE-HlyAs, the secretion efficiency was determined to be about 300 microg L(-1) by Western blotting.