Rhizobium trifolii capsular polysaccharide

Table A31 Structure 47 Rhizobium trifolii Capsular Polysaccharide ...

Figure 1. An x-ray diffraction pattern from an oriented, noncrystalline fiber of the Rhizobium trifolii capsular polysaccharide using CuKa radiation. (Reproduced with permission from Ref. 16. Copyright 1987 Gordon and Breach.)...

Using computer modeling, jointly with x-ray fiber diffraction data, the molecular architectures of two different gel-forming polysaccharides have been examined. Preliminary results indicate that the neutral and doubly branched capsular polysaccharide from Rhizobium trifolii can form a 2-fold single helix of pitch 1.96 nm or a half-staggered, 4-fold doublehelix of pitch 3.92 nm. The molecules are likely to be stabilized by main chain — side chain interactions. 

Studies on the white clover -Rhizobium trifolii interaction are the most advanced. Trifoliin A, a lectin present in clover-seedling roots, binds hapten reversibly to carbohydrate antigens cross-reactive on the capsular polysaccharide of R. trifolii and clover epidermal-cells.244 A specific hapten that inhibits binding of trifoliin A to both surfaces is 2-deoxy-D-arabino-hexose.245 It has also been shown that levels of trifoliin A on root hairs decline with increasing concentrations of nitrate, in parallel to root-nodule development,246 and that lectin receptors are transient on R. trifolii, in a way coinciding with its capacity to be adsorbed to clover roots.247... 

The economic importance of nitrogen-fixation by leguminous plants has led to extensive study of the process of nodulation and in particular the nature of the host specificity of Rhizobium. Antiserum raised to clover tissue reacts with virulent strains of R. trifolii and to a lesser extent with avirulent strains of the same organism. If the antiserum is pretreated with avirulent cells a purified antibody, specific for the virulent strain, can be prepared. The purified antisera will bind to R. trifolii virulent strains and clover cells, but not to incompatible Rhizobium species. Immunofluorescence can be used to demonstrate that antisera raised against the capsular polysaccharide of R. trifolii binds to the surface of clover root cells, in particular to the tips of the root hairs. Chemical analysis of this capsule shows that it... 

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