The synthesis, secretion and role in virulence of the paracrystalline surface protein layers of Aeromonas salmonicida and A. hydrophila.

The S-layers of the Aeromonas spp. studied to date are composed of identical protein subunits which are translocated across the cytoplasmic membrane, periplasm and outer membrane to the cell surface, where they are assembled and tethered to the cell via an interaction with the O-polysaccharide side chains of the lipopolysaccharide. Aeromonas S-layers have the ability to bind a number of host factors such as fibronectin, laminin and vitronectin as well as providing resistance to serum killing and protease digestion. Aeromonas mutants unable to produce an S-layer are altered in their ability to cause disease. In the case of Aeromonas salmonicida, the loss of ability to produce an S-layer effectively abolishes virulence. However, in the case of A. hydrophila, the reduction in virulence caused by the loss of the S-layer is less significant.