Structure of the O-polysaccharide of Azorhizobium caulinodans HAMBI 216; identification of 3-C-methyl-d-rhamnose as a component of bacterial polysaccharides

The O-polysaccharide was obtained from the lipopolysaccharide of the stem-nodulating nitrogen-fixing bacterium Azorhizobium caulinodans HAMBI 216 and studied by sugar and methylation analyses along with 1H and 13C NMR spectroscopy. The polysaccharide was found to have a linear pentasaccharide repeating unit containing d-rhamnose and its rarely occurring 2-O-methyl (Rha2OMe) and 3-C-methyl (Rha3CMe) derivatives and having the following structure:→3)-α-d-Rhap2OMe-(1→2)-β-d-Rhap3CMe-(1→3)-α-d-Rhap-(1→2)-β-d-Rhap3CMe-(1→3)-α-d-Rhap-(1→

Graphical abstract→3)-α-d-Rhap2OMe-(1→2)-β-d-Rhap3CMe-(1→3)-α-d-Rhap-(1→2)-β-d-Rhap3CMe-(1→3)-α-d-Rhap-(1→Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The O-polysaccharide (OPS) of nitrogen-fixing bacterium A. caulinodans was obtained. ► The OPS repeating unit contains d-Rha and its Rha2OMe and Rha3CMe derivatives. ► The OPS peculiarity is the presence of the rarely occurring residue of Rha3CMe.