Comparative studies of extracellular polysaccharide elaborated by Rhizobium meliloti strain M5N1 in defined medium and in non-growing cell suspensions

Abstract

Rhizobium meliloti, a soil inhabiting bacterium, produces water soluble polysaccharides in RC medium and under resting-cell conditions. The polysaccharides produced by growing and non-growing bacteria have been isolated, purified and determined to contain glucose, galactose, pyruvic acid, acetic acid, and succinic acid in the approximate molar ratio of 7:1:1:3:1:1:1 with β(1 a ̊ 3), β(1 a ̊ 6), and β(1 a ̊ 6) , glycosidic linkages. The rheological properties of the polysaccharides have been investigated and were shown to differ according to the origin of the polysaccharide. A major difference was observed in the intrinsic viscosities, 8000 ml/g and about 40 000 ml/g for molecules obtained from growing and non-growing bacteria respectively. The viscosities of both polysaccharides were slightly sensitive to salt and were stable over a range of pH from 1 to 11. Measurements of optical rotation versus temperature revealed a sharp transition at T M = 76° C associated with a partial irreversible decrease in viscosity.