Structure and genetics of the O-antigen of Escherichia coli O169 related to the O-antigen of Shigella boydii type 6

•The O-antigen repeating unit carries two side-chain residues on the same branch-point residue.•The glucosyltransferase gene for the β-(1→6)-linkage in the side-chain is between gnd and galF.•The backbone of the polysaccharide has structural elements in common with the Escherichia coli O175 O-antigen.

The O-polysaccharide (O-antigen) of Escherichia coli O169 was studied by sugar analysis along with 1D and 2D 1H and 13C NMR spectroscopy. The following structure of the branched hexasaccharide repeating unit was established: Figure optionsDownload full-size imageDownload as PowerPoint slideThe O-polysaccharide of E. coli O169 differs from that of Shigella boydii type 6 only in the presence of a side-chain glucose residue. A comparison of the O-antigen biosynthesis gene clusters between the galF to gnd genes in the genomes of the two bacteria revealed their close relationship. The glycosyltransferase gene responsible for the formation of the β-d-Glcp-(1→6)-α-d-Galp linkage in the O-antigen was identified in the gene cluster.

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