Structure and genetics of the O-antigen of Enterobacter cloacae G3054 containing di-N-acetylpseudaminic acid.

Mild acid degradation of the lipopolysaccharide of Enterobacter cloacae G3054 resulted in the cleavage of the O-polysaccharide at the linkage of residues of 5,7-diacetamido-3,5,7,9-tetradeoxy-L-glycero-L-manno-non-2-ulosonic acid (di-N-acetylpseudaminic acid, Pse5Ac7Ac) in the main chain. The resultant oligosaccharide and an alkali-treated lipopolysaccharide were studied by sugar analysis along with (1)H and (13)C NMR spectroscopy, and the following structure of the branched pentasaccharide O-unit of the O-polysaccharide was established: [structure: see text] The O-antigen gene cluster of E. cloacae G3054 between conserved genes galF and gnd was sequenced. Most genes necessary for the O-antigen synthesis were found in the cluster and their functions were tentatively assigned by comparison with sequences in the available databases.