O-polysaccharide structure in serogroup I azospirilla

Abstract

Lipopolysaccharides (LPS) and O-specific polysaccharides (OPS) were obtained from the outer membrane of four Azospirillum strains previously assigned to serogroup I based on the serological affinity revealed by the antibodies (AB) to the LPS of A. brasilense Sp245. Investigation, including determination of monosaccharide composition, methylation analysis, and one- and two-dimensional NMR spectroscopy, was carried out to determine the OPS structure. The OPSs of A. brasilense Sp107 and S27 and of A. lipoferum RG20a were found to have an identical structure of repeating units represented by a linear penta-D-rhamnan, as was previously described for the OPSs of A. brasilense Sp245 and SR75. The OPS of A. brasilense SR15 was found to consist of tetrasaccharide repeating units of the following structure: → 2)-α-D-Rhap-(1 → 2)-β-D-Rhap-(1 → 3)-α-D-Rhap-(1 → 2)-α-D-Rhap-(1 →. An opine compound, Nδ-(1-carboxyethyl)-ornithine, closely associated with the LPS of A. brasilense SR15, was identified in azospirilla for the first time. The presence of a 6-deoxisugar (D-rhamnose) in the OPS structure was shown to be the chemical basis of the serological similarity and the reason for classification of these strains within the serogroup I.