The existing research papers have demonstrated the strong immunogenicity of outer membrane proteins to aquacultured creatures.Using the previously constructed recombinant plasmid pET30a-OmpK as template,the peptide coding sequence of OmpK was amplified by PCR.After introducing restriction sites at both 5′ ends and 3′ends of the sequence,the gene was cloned into secreted expression vector pPIC9K,and formed the recombinant vector pPIC9K-OmpK.The vector was linearized bySalⅠ,and transformed into Pichia pastoris strain GS115 by the method of Lithium Chloride transformation.Transformants were selected by G418 and confirmed by PCR.The recombinant protein was expressed and secreted into the supernatant after inducing by methanol.SDS-PAGE analysis indicated the recombinant protein OmpK was hyperglycosylated with a molecular weight about 37 ku,larger than the expected size 29 ku.Western-blotting results showed that the recombinant protein OmpK could react with the antiserum against OmpK expressed by E.coli BL21.It indicated that the protein OmpK was glycosylated but remained its antigenicity.