A (1-]4)-BETA-D-GLUCURONAN EXCRETED BY A MUTANT OF THE RHIZOBIUM-MELILOTI M5N1 STRAIN

A mutant of the R. meliloti M5N1 strain has been selected. This strain , R. meliloti M5N1 CS (NCIMB 40472), excretes an extracellular materia l composed of 2-O-Ac-beta-GlcpA, 3-O-Ac-beta-GlcpA, 2,3-di-O-Ac-beta-G lcpA and three species of beta-GlcpA residues 1-->4 linked. For the cu lture conditions used, the weight average molecular weight of the poly mer varied in the range of 6 x 10(4) < MwBAR < 4 x 10(5). High molecul ar weight glucuronate forms thermoreversible gels at 5 g L-1. In the p resence of divalent cation such as Ca2+ or trivalent cations such as C r3+ or Fe3+, Cross linking of the polymer occurs. This polysaccharide is the first exocellular (1-->4)-beta-D-glucuronan produced by a R. me liloti strain.