Structural characterization of a new acidic exopolysaccharide and cyclic (1→2) β-glucan produced by Rhizobium huakuii forming nodules on Astragalus sinicus

Rhizobium huakuii isolated from root nodules of Astragalus sinicus produced a new acidic exopolysaccharide composed of glucose, galactose, ribose, and glucuronic acid in an approximate molar ratio of 5 : 1 : 1 : 1. Degradation with an enzyme capable of specifically hydrolyzing succinoglycan and methylation analyses suggested that the main chain of the new exopolysaccharide has a common structure with acidic exopolysaccharides from Agrobacterium sp. and Rhizobium meliloti. The distribution pattern of the degrees of polymerization in cyclic (1→2) β-glucans of R. huakuii was more similar to that of R. meliloti than that of Agrobacterium sp.