STRUCTURE OF AMYLOVORAN, THE CAPSULAR EXOPOLYSACCHARIDE FROM THE FIREBLIGHT PATHOGEN ERWINIA-AMYLOVORA

The acidic exopolysaccharide (EPS) of Erwinia amylovora, amylovoran, w as purified from culture supernatants of bacteria in minimal medium an d cleaved chemically either by treatment with trifluoroacetic acid or hydrofluoric acid, and enzymatically by digestion with depolymerase fr om E. amylovora phage phi-Ea1h. Structural characterization of the res ulting oligosaccharides was performed by a combination of mass spectro metric and NMR [one- and two-dimensional (1D and 2D)] spectroscopic te chniques, A branched repeating unit with five monosaccharide residues and various substituents was determined: [Graphics] The terminal monos accharide of the side branch, which bears a 4,6-bound pyruvate residue in the R-configuration, was found to be modified with 2-linked (26%), 3-linked (24%), 2-,3-linked (40%) O-acetyl groups, or these were abse nt (10%). An additional glucose residue is linked to approximately 10% of the core alpha-galactose of the repeating unit. (c) 1996 Elsevier Science Ltd.