An outer membrane protein, OmpK, is an effective vaccine candidate for Vibrio harveyi in Orange-spotted grouper (Epinephelus coioides)

The outer membrane proteins of the fish pathogen, Vibrio harveyi, have a role in interaction between bacterium and host and are potential candidates for vaccine development. In this study, the gene encoding an outer membrane protein, OmpK, which serves as the receptor for broad-host-range vibriophage KVP40 in V. harveyi, was isolated and characterized. Then the OmpK gene coding for mature peptide was subcloned into prokaryotic expression vector pBV220 and transformed into Escherichia coli DH5 alpha strain. After temperature induction, a recombinant protein was detected about 28 kDa in molecular weight and accounted for 24.8% of total proteins of whole cell as estimated by SDS-PAGE and scanning analysis of gel image. Polyclonal antibodies were raised in rabbits against the purified protein and the reaction of the antibody was confirmed by western blotting using the purified protein and crude extract of V. harveyi. Orange-spotted groupers (Epinephelus coioides) vaccinated with recombinant OmpK produced specific antibodies, and were highly resistant to infection by virulent V. harveyi. These results indicate that the OmpK is an effective vaccine candidate against V. harveyi in Orange-spotted groupers.