Structural Analysis of the Capsular Polysaccharide from Sinorhizobium fredii HWG35

• Published in: Biomacromolecules Vol. 6; no. 3; pp. 1448 - 1456
• Main Authors: Rodríguez-Carvajal, Miguel A, Rodrigues, Joao A, Soria-Díaz, María E, Tejero-Mateo, Pilar, Buendía-Clavería, Ana, Gutiérrez, Rocío, Ruiz-Sainz, Jose E, Thomas-Oates, Jane, Gil-Serrano, Antonio M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.05.2005
• Subjects: Applied sciences; Carbohydrate Conformation; Exact sciences and technology; Natural polymers; Physicochemistry of polymers; Polysaccharides, Bacterial - analysis; Polysaccharides, Bacterial - chemistry; Sinorhizobium fredii; Sinorhizobium fredii - isolation & purification; Starch and polysaccharides; Purification; Microbial origin; Molecular structure; Absolute configuration; Bacteria; Oside polymer; Chemical isolation; Rhizobiaceae; Experimental study; Extracellular; Rhizobium fredii
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm049264u

We have determined the structure of a capsular polysaccharide from Sinorhizobium fredii HWG35. This polysaccharide was isolated following the standard protocols applied for lipopolysaccharide isolation. On the basis of monosaccharide analysis, methylation analysis, mass spectrometric analysis, one-dimensional 1H and 13C NMR, and two-dimensional NMR experiments, the structure was shown to consist of a polymer having the following disaccharide repeating unit:  →6)-2,4-di-O-methyl-α-d-Galp-(1→4)-β-d-GlcpA-(1→. Strain HWG35 produces a capsular polysaccharide that does not show the structural motif (sugar-Kdx) observed in those S. fredii strains that, while effective with Asiatic soybean cultivars, are unable to form nitrogen-fixing nodules with American soybean cultivars. Instead, the structure of the capsular polysaccharide of S. fredii HWG35 is in line with those produced by strains HH303 (rhamnose and galacturonic acid) and B33 (4-O-methylglucose-3-O-methylglucuronic acid), two S. fredii strains that form nitrogen-fixing nodules with both groups of soybean cultivars. Hence, in these three strains that effectively nodulate American soybean cultivars, the repeating unit of the capsular polysaccharide is composed of two hexoses, one neutral (methylgalactose, rhamnose, or methylglucose) and the other acidic (glucuronic, galacturonic, or methylglucuronic acid).