A CONSERVED AEROMONAS-SALMONICIDA PORIN PROVIDES PROTECTIVE IMMUNITY TO RAINBOW-TROUT

A protein with an apparent M(r) of 28,000 was isolated from outer memb rane preparations of Aeromonas salmonicida A440. The protein was teste d for the ability to form pores, using a planar lipid bilayer model me mbrane system. The protein appeared to be a monomer with a single-chan nel conductance in 1.0 M KCl of 1.96 nS and a cation/anion permeabilit y ratio of 2.91 +/- 0.68. These data show that the porin channel is co mparable in size to OmpC and OmpF of Escherichia coli and is relativel y nonselective, having some preference for cations over anions. The po rin was purified by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and a polyclonal antibody was raised. Immunoblot analysis showed that an immunologically cross-reactive protein was pre sent in other Aeromonas strains but not in strains of Vibrio or Yersin ia. The N-terminal amino acid sequence of the porin was determined and was found to show some homology to an Aeromonas hydrophila outer memb rane protein. This is the second porin species of A. salmonicida to be described, and it differs from the other in subunit molecular weight, aggregation properties, peptidoglycan association, pore size, and ant igenicity. Rainbow trout (Oncorhynchus mykiss) immunized intraperitone ally with the purified porin protein were significantly protected from experimental A. salmonicida challenge. This is the first report of su ccessful vaccination against A. salmonicida with a purified outer memb rane component.