Functional genomics of the Aeromonas salmonicida lipopolysaccharide O-antigen and A-layer from typical and atypical strains

The A. salmonicida A450 LPS O-antigen, encoded by the wb salmo gene cluster, is exported through an ABC-2 trans porter-dependent pathway. It re presents the first example of an O-antigen LPS polysaccharide with three different monosaccharides in their repeating unit assembled by this pathway. Until now, only repeating units with one or two different monosaccharides have been described. F unctional genomic analysis of this wb salmo region is mostly in agreement with the LPS O-antigen structure of acetylated L -rhamnose (Rha), D -glucose (Glc), and 2-amino-2-deoxy- D -mannose (ManN). Between genes of the wb salmo we found the genes responsible for the biosynthe sis and assembly of the S-layer (named A-layer in these strains). Through comparative genomic analysis and in-frame deletions of some of the genes, we concluded that all the A. salmonicida typical and at ypical strains, other than A. salmonicida subsp. pectinolytica strains, shared the same wb salmo and presence of A-layer. A. salmonicida subsp. pectinolytica strains lack wb salmo and A-layer, two major virulence factors, and th is could be the reason they ar e the only ones not found as fish pathogens