Expression of Vibrio harveyi ompK in the yeast Pichia pastoris: The first step in developing an oral vaccine against vibriosis?

OmpK, one of the major outer-membrane proteins of Vibrio harveyi zj2008, was expressed in cells of the yeast Pichia pastoris GS115. After induction for 72 h in methanol-containing medium, the concentration of the expressed protein reached 2 μg mL−1. The recombinant protein was well recognized by antibody against Escherichia coli-expressed ompK in Western blotting analysis. Alginate microspheres containing the recombinant protein were prepared and fed to sea bass (Lateolabrax japonicus). ELISA analysis indicated that a significant antibody response against ompK was elicited in the vaccinated group. Challenge of vaccinated fish with V. harveyi zj2008 revealed that immunization provided protection against the pathogen. These results suggest that P. pastoris expressing ompK is a feasible means of generating an antigen that can protect marine fish against vibriosis. Thus, alginate microspheres encapsulating the antigen may be developed as an oral vaccine in the near future.