GELATION OF MEMBERS OF A FAMILY OF BRANCHED ANIONIC HETEROPOLYSACCHARIDES PRODUCED BY CERTAIN STRAINS OF RHIZOBIUM-LEGUMINOSARUM

The structure of the anionic extracellular slime produced by Rhizobium leguminosarum biovar phaseoli 8002 has been shown to be unaltered by variation of the Sym plasmid. The polysaccharide is a member of a family of branched-anionic polysaccharides. Rheological studies have demonstrated gelation of members of this family of polysaccharides produced by certain R. leguminosarum strains. Gelation was found to be dependent upon the ionic strength and salt composition of the sample. Aqueous preparations of the purified polysaccharides did not gel. Thermoversible gels were formed upon addition of salts to the aqueous preparations. Divalent cations were found to be more effective than monovalent cations in promoting gelation. Possible consequences of the gelation of the extracellular polysaccharides, relating to non-specific adhesion of the bacteria to plant roots, water retention in soils, and soil aggregation and stability, are discussed. © 1990.