Structure of the O polysaccharide and serological classification of Pseudomonas syringae pv. ribicola NCPPB 1010

The O polysaccharide (OPS) moiety of the lipopolysaccharide (LPS) of a phyt opathogenic bacterium Pseudomonas syringae pv. ribicola NCPPB 1010 was stud ied by sugar and methylation analyses, Smith degradation, and H-1- and C-13 -NMR spectroscopy, including 2D COSY, TOCSY, NOESY and H-detected H-1,C-13 HMQC experiments. The OPS structure was elucidated, and shown to be compose d of branched pentasaccharide repeating units (O repeats) of two types, maj or (1) and minor (2), differing in the position of substitution of one of t he rhamnose residues. Both O repeats form structurally homogeneous blocks w ithin the same polysaccharide molecule. [GRAPHICS] Although P. syringae pv. ribicola NCPPB 1010 demonstrates genetic relatedne ss and similarity in the OPS chemical structure to some other P. syringae p athovars, it did not cross-react with any OPS-specific mAbs produced agains t heterologous P. syringae strains. Therefore, we propose to classify P. sy ringae pv. ribicola NCPPB 1010 in a new serogroup, O8.