ISOLATION OF AN EXTRACELLULAR POLYSACCHARIDE (EPS) DEPOLYMERASE PRODUCED BY BRADYRHIZOBIUM-JAPONICUM

Bradyrhizobium japonicum is capable of producing an acidic, high molecular weight, extracellular polysaccharide (EPS). An enzyme exhibiting EPS depolymerase activity was detected in cell lysates of B. japonicum strain 2143. The depolymerase was active against the EPS produced by strain 2143 and the closely related EPS produced by strain 311b 110. Depolymerase activity was characterized by its ability to decrease the viscosity of EPS solutions, to decrease the molecular weight of EPS, and to catalyze the release of reducing groups from EPS. The depolymerase exhibited a sharp activity optimum at pH 6 and had a molecular weight of approximately 45 kD as determined by gel permeation chromatography. Analysis of depolymerase-treated EPS indicates that the enzyme acts as an endo-depolymerase, producing a relatively narrow size range of high molecular weight products. © 1990 Springer-Verlag New York Inc.