Extracellular polysaccharide of Erwinia chrysanthemi

The extracellular polysaccharide (EPS) produced by E. chrysanthemi pv. zeae strain SR260, a strain pathogenic to corn, has a branched hexasaccharide repeat unit consisting of a glucomannorhamnan backbone [ → 3)-β- d - Glc p-(1 → 4)-α- d - Man p-(1 → 3)-α- l - Rha p-(1 → ] and a trisaccharide side-chain [ α- l - Rha p-(1 → 3)-α- l - Rha p-(1 → 4)?- GlcA p-(1 → ] attached to O-3 of the mannose in the backbone [1]. All the anomeric configurations, except that of the rhamnosyl-glucosyluronic linkage in the side chain, were unambiguously assigned by a combination of 1 and 2D NMR spectroscopy. The tentative assignment of the rhamnosyl-glucosyluronic glycosyl linkage as α- l is now proven.