Extracellular Polysaccharide by Bradyrhizobium japonicum: Production and Characterization

Abstract

An exopolysaccharide from Bradyrhizobium japonicum has been produced, purified and characterized. It is mainly composed of carbohydrates (86 ± 4.5%) and uronic acids (14 ± 1%). The relative proportions are: carbohy drates—glucose 84%, galactose 14%, mannose 2%; uronic acids—glucuronic 83%, galacturonic 10%, mannuronic 3%, arabinuronic 4%. The IR spectrum in dicates the presence of ether, ester, hydrogen bonds and a β-type bond between the monomers. DSC analysis revealed the presence of two transition peaks: the first in the temperature range 117-153 ° C due to bound water and the second at 292°C due to thermal decomposition of the polymer. Viscosity measure ments of water solutions as a function of polymer concentration in the range 0.33-1% w/w allowed the determination of the consistency coefficient and be haviour index. Taking into account the dependence on temperature, a general relation of viscosity as a function of polymer concentration, temperature and shear rate has been proposed.