Structural studies of the O-polysaccharide chain from the lipopolysaccharide of symbiotically enhanced mutant Mlo-13 of Mesorhizobium loti NZP2213

The O-specific polysaccharide (OPS) of Mesorhizobium loti mutant Mlo-13 was obtained by mild-acid degradation of the lipopolysaccharide and studied by sugar and ethylation analyses, Smith degradation, as well as 1H and 13C NMR spectroscopy. The O-polysaccharide has a trisaccharide repeating unit composed of 6-deoxy-l-talose (l-6dTal), 4-O-acetyl-6-deoxy-l-talose (l-6dTal-4Ac) and l-rhamnose residues. An analysis of NMR spectra revealed that the rhamnose residue was substituted nonstoichiometrically with O-methyl group at C-3. The following structure of the repeating unit of the Mlo-13 OPS was established: