Possible biological roles for Rhizobium leguminosarum extracellular polysaccharide and cyclic glucans in bacteria-plant interactions for nitrogen-fixing bacteria

The extracellular polysaccharide (EPS) secreted by Rhizobium leguminosarum forms an aqueous solution. Addition of electrolyte can lead to the formation of transparent thermoreversible gels. A non-specific role for EPS gelation in the initial attachment of the bacteria to plant material is suggested. Techniques have been developed for the preparation of cyclic glucans from EPS − R.leguminosarum. The preparation, purification and characterization of ring sizes will be described. Evidence will be presented that cyclic glucans solubilize naringenin, a flavonoid known to induce nodulation genes. A biological role for cyclic glucans in accumulating naringenin is proposed.