Exopolysaccharides from Rhizobium meliloti YE-2 grown under different osmolarity conditions: viscoelastic properties

The exopolysaccharides fro Rhizobium meliloti YE-2 extracted 10 days after the inoculum from culture broths and having different osmolarity values (0, 0.2, 0.4, and 0.6 M) have been investigated by means of oscillatory and steady-shear measurements on 1% solutions in 0.1M NaCl. The micro-organism produces a mixture of a galactoglucan and a succinoglycan. At low osmolarity (0 and 0.2M), the main fraction consists of galactoglucan and the viscoelastic properties of the mixture are typical of an entanglement system. At 0.4 and 0.6M, the proportion of the succinoglycan increases and the viscoelastic properties change abruptly to those typical of a "weak gel" system. Different conformations are adopted by the two exopolysaccharides in solution.