[The structure of the O-specific polysaccharide from a mutant of nitrogen-fixing rhizobacterium Azospirillum brasilense Sp245 with an altered plasmid content].

The rhizobacteria Azospirillum brasilense Sp245 produce antigenically different lipopolysaccharides LPSI and LPSII, both containing identical pentasaccharides built from D-rhamnose residues as the repeated chains of O-specific oligosaccharides (OPS). In this study, we report the structure of the OPS from A. brasilense LPSI(-)LPSII(-)-mutant Sp245.5, which spontaneously lost the p85 and p120 plasmids upon the formation of a new 300-MDa megaplasmid after the long-term storage of the bacteria in a rich medium. The repeating unit of the A. brasilense mutant Sp245.5 appeared to be a disaccharide consisting of residues of N-acetyl-D-galactosamine and N-acetyl-D-mannosaminuronic acid: [Formula: see text].