THE A-LAYER PROTEIN OF AEROMONAS-SALMONICIDA - FURTHER CHARACTERIZATION AND A NEW ISOLATION PROCEDURE

The predominant cell surface protein (A-protein) of Aeromonas salmonicida has been purified by a method utilizing a glycine/hydrochloride extraction from whole cells and HPLC/ion exchanger (DEAE) columns. This procedure yielded two LPS-free molecules (a 40- and a 50-kDa form) both shown to contain A-protein determinants. The former appears to be a digest product of the latter, as a serine protease produced by A. salmonicida was shown to process the 50-kDa form into a 40-kDa molecule in vitro. The A-layer protein was shown to contain one isoform, although multiple isoelectric forms appeared as preparative artifacts, probably due to deamidation. The A-layer protein and LPS are the most significant surface antigens recognized by the Atlantic salmon B-lymphocytes or antibodies. Immunological studies of LPS-free and LPS-containing A-protein preparations were undertaken to test whether the two components behave like antigenic competitors or whether the LPS moiety could adjuvant the antibody response against the A-protein. The latter was shown to be the case.