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-Glcp-(1 → 4)-α-d-Manp-(1 → 3)-α-l-Rhap-(1 →] and a trisaccharide side-chain [α-l-Rhap-(1 → 3)-α-l-Rhap-(1 → 4)?-GlcAp-(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.