Structural determination of the phytotoxic mannan exopolysaccharide from Pseudomonas syringae pv. ciccaronei

The structural determination was performed of a mannan exopolysaccharide fr om the Gram negative bacterium Pseudomonas syringae pv. ciccaronei, which i s the pathogenic agent responsible for the leaf spots of carob plants. The structure, obtained by chemical, enzymatic and spectroscopic methods, consi sted of a backbone of alpha-(1 --> 6)-linked mannopyranose units with 80% s ubstituted at C-2 by mono-, di- and trisaccharide side chains. In addition, terminal glucose units and phosphate groups were found to be present. This is, to the best of our knowledge, the first report of a mannan exopolysacc haride structure from a phytopathogenic bacterium. The pure polysaccharide showed phytotoxic effects, i.e., chlorosis and necrosis on tobacco leaves. (C) 2001 Elsevier Science Ltd. All rights reserved.