Purification, and biochemical and structural characterization of a fimbrial haemagglutinin of Renibacterium salmoninarum

Renibacterium salmoninarum was shown to possess peritrichous fimbriae. Electron microscopy of strains FMV 84-01 and ATCC 33209T revealed short, flexible fimbriae less than 2 nm in diameter. These surface appendages were isolated from the bacteria by a procedure involving water extraction and urea solubilization. The fimbrin was purified to homogeneity by Fast Pressure Liquid Chromatography, and shown by SDS-PAGE to be a protein of 57 kDa. Isoelectric focusing under non-denaturing conditions indicated a pI of 4.8. The protein had an amino acid composition rich in glycine, Asx (aspartic acid and asparagine), valine and alanine; methionine was absent. Approximately 33% of the amino acid residues were hydrophobic. Immunoblotting using a polyclonal antiserum raised against whole cells showed that the 57 kDa protein was the immunodominant antigen on the cell surface. Immunogold labelling using polyclonal antibodies raised against the fimbrin revealed an alignment of gold particles along the fimbriae. Purified fimbriae caused agglutination of rabbit erythrocytes and antifimbrial serum inhibited this haemagglutination. Altogether the results indicate that the fimbriae on the surface of R. salmoninarum are responsible for the haemagglutinating activity.