Immunological characterization of a bacterial protein isolated from salmonid fish naturally infected withPiscirickettsia salmonis

The Salmon Rickettsia syndrome (SRS) remains a major infectious disease in the Chilean aquaculture. A limited number ofPiscirickettsia salmonisproteins have been characterized so far for their use as potential candidates for vaccines studies. In this study, we identified and expressed a highly immunogenic protein ofP. salmonisextracted by selective hydrophobicity from crude-cell macerates of naturally infected salmonid fish. One and two-D PAGE gels followed by Western blot analysis with a battery of polyclonal anti-P. salmonisantibodies have allowed the isolation of the target protein. Basic local alignment search (BLAST) done after partial sequencing of the pure protein identified it as a member of the heat-shock protein (HSP) family of prokaryotes. The protein, named ChaPs, was cloned as a single open reading frame encoding 545 amino acid residues with a predicted molecular mass of 57.3kDa. The amplicon representing the entire novel gene was expressedin vitroin different heterologous systems: the PureProCaulobacter crescentusexpression system from where most of the characterization was attained, and also in theEscherichia coliBL-21 CodonPlus model for commercially potential purposes.The immunologic potential of ChaPs was determined with serum from naturally infected fish.