IMMUNE DIFFUSION ANALYSIS OF THE EXTRACELLULAR SOLUBLE ANTIGENS OF TWO STRAINS OFRHIZOBIUM MELILOTI

Abstract

Immune diffusion technics applied to cultures of two strains of R. meliloti grown in liquid defined medium showed the presence of multiple antigens. Improved resolution of precipitin patterns was obtained with concentrated antigens separated from the cultures as the extracellular soluble fraction or as suspensions of washed cells. The extracellular fraction contained the same diffusible antigens as the washed cells, but additional antigens were found in the cells after ultrasonic disruption. The extracellular soluble antigens were shown by analysis to contain polysaccharide and protein components. In immune diffusion systems, they gave rise to three groups of precipitin bands, two of which were characterized as polysaccharides by their susceptibility to periodate oxidation, and the third as protein by its lability to heat. All the extracellular antigens of both strains were shared except a fast-diffusing polysaccharide, which was specific for each strain. Despite the sharing of all but one of their antigens, cells of these strains showed only a low degree of cross-agglutination, suggesting that their surfaces are dominated by the specific polysaccharide. No differences could be found in the composition of the polysaccharides in the unfractionated extracellular antigens of the two strains, the main components of which were glucose (66%) and galactose (12%) in the presence of several other unidentified sugars in smaller amounts. The pattern of precipitin bands produced in immune diffusion systems by the extracellular soluble fraction could be changed by altering the cultural conditions.