Structure of the O-specific polysaccharide of Aeromonas veronii bv. sobria strain Pt393 isolated from rainbow trout (Oncorhynchus mykiss), which contains a rarely occurring sugar 4-acetamido-4,6-dideoxy-d-galactose, tomosamine.

The O-specific polysaccharide (OPS) was isolated from the lipopolysaccharide of Aeromonas veronii bv. sobria strain Pt393, which is pathogenic to the rainbow trout (Oncorhynchus mykiss), after mild acid hydrolysis followed by GPC. The high-molecular-weight OPS fraction was studied with chemical methods, mass spectrometry, and H and C NMR spectroscopy techniques, including 2D H,H COSY, TOCSY, NOESY, H-detected heteronuclear H,C HSQC, and HMBC experiments. It was found that the O-specific polysaccharide was built of a tetrasaccharide repeating unit composed of α-GalpNAc, α-FucpNAc, β-QuipNAc, and α-Fucp4NAc (4-acetamido-4,6-dideoxy-d-galactose, tomosamine) residues. The following structure of the OPS of A. sobria strain Pt393 was established: →4)-α-d-GalpNAc-(1 → 3)-α-l-FucpNAc-(1 → 3)-β-d-QuipNAc-(1 → 3)-α-d-Fucp4NAc-(1→.