SOLUTION PROPERTIES OF EXOCELLULAR POLYSACCHARIDES OF RHIZOBIUM-LEGUMINOSARUM - STATIC AND DYNAMIC LIGHT-SCATTERING - CHARACTERIZATION IN DILUTE-SOLUTION

Three polysaccharides, Rhizobium leguminosarum 8002 EPS(I), Rhizobium trifolii TA1-EPS (II), Rhizobium leguminosarum 127K87 EPS (III), produ ced by bacteria of Rhizobium genus have been investigated by static an d dynamic light scattering combined with chirooptical measurements. Al l three polymers have the same backbone but differ in the length of th e side chains and in the content of minor substituents. An isothermal conformational transition coil --> helix was observed with I and II by adding salt (NaCl). The molecular parameters of the polysaccharides i n the ordered state were determined by light-scattering data. Increasi ng the ionic strength a shrinking of the helix was observed accompanie d by a corresponding decrease in the radius of gyration. An extraordin ary chain stiffness in terms of Kuhn segment lengths was found in both cases, similar to that already observed for other microbial polysacch arides. In the case of III no disorder --> order transition was induce d by the salt, and the scattering behavior corresponds to that of a ra ther flexible polymer with a characteristic ratio C-infinity = 24. The incapability of III to form a helical structure is attributed to the effect of the very long side chain. The analysis of the time correlati on functions revealed typical flexible chain behavior for all three po lysaccharides. This behavior for the two ordered polymers is in agreem ent with a recent theory by Maggs and is due to bending modes of the r ods. (C) 1995 John Wiley and Sons, Inc.