Structures of two O-chain polysaccharides of Citrobacter gillenii O9a,9b lipopolysaccharide. A new homopolymer of 4-amino-4,6-dideoxy-D-mannose (perosamine).

Mild acid degradation of the lipopolysaccharide of Citro- bacter gillenii O9a,9b released a polysaccharide (PS), which was found to consist of a single monosaccharide, 4- acetamido-4,6-dideoxy-d-mannose (d-Rha4NAc, N-acetyl-d-perosamine). PS was studied by methylation analysis and (1)H-NMR and (13)C-NMR spectroscopy, using two-dimensional (1)H,(1)H COSY, TOCSY, NOESY, and H-detected (1)H,(13)C heteronuclear correlation experiments. It was found that PS includes two structurally different polysaccharides: an alpha1-->2-linked homopolymer of N-acetyl-d-perosamine [-->2)-alpha-d-Rhap4NAc-(1-->, PS2] and a polysaccharide composed of tetrasaccharide repeating units (PS1) with the following structure: -->3)-alpha-d-Rhap4NAc-(1-->2)-alpha-d-Rhap4NAc-(1-->2)-alpha-d-Rhap4NAc-(1-->3)-alpha-d-Rhap4 N Ac2Ac-(1--> where the degree of O-acetylation of a 3-substituted Rha4NAc residue at position 2 is approximately 70%. PS could be fractionated into PS1 and PS2 by gel-permeation chromatography on TSK HW-50S. Matrix-assisted laser desorption ionization MS data indicate sequential chain elongation of both PS1 and PS2 by a single sugar unit, with O-acetylation in PS1 beginning at a certain chain length. Anti-(C. gillenii O9a,9b) serum reacted with PS1 in double immunodiffusion and immunoblotting, whereas neither PS2 nor the lipopolysaccharide of Vibrio cholerae O1 with a structurally related O-chain polysaccharide were reactive.