X. campestris, the type species of Xanthomonas, is an aerobic Gram-negative bacterium belonging to the Pseudomonoadaceae; many strains of this species are phytopathogenic. Data on the composition and structure of the surface polysaccharides of X. campestris may serve as a chemotaxonomic criterion and allow one to determine its relationship to other bacteria, particularly to Pseudomonas. An exopolysaccharide of X. campestris, xanthan, has been actively studied', whereas data on outer membrane lipopolysaccharides (LPSs) are limited2s3. The uncommon sugars b-rhamnose and 3-acetamido-3,6-dideoxy-p-galactose have been identified as components of the strain B-1459 LPS3.
We report now the structure of the O-specific polysaccharide of LPS from X campestris strain NCPPB 45.
The LPS was extracted by the phenol-water procedure4 and cleaved with 1% CH,COOH to give an acidic O-specific polysaccharide (PS) isolated from the water-soluble portion by gel-permeation chromatography on Sephadex G-50 and purified by anion-exchange chromatography on DEAE-Toyopearl 650M. The PS had [olD + 22" (c 0.4).
Acid hydrolysis of the PS revealed the presence of rhamnose, galactose, and galacturonic acid, which were identified by TLC.
The 13C NMR spectrum of the PS was typical of a regular polymer (Fig. 1). In the region of the anomeric carbon resonances, there were six signals, with nearly equal intensities, pointing to a hexasaccharide repeating unit. The spectrum