Low-molecular-weight polysaccharide antigens isolated from Rhodopseudomonas gelatinosa.

Strain-specific low-molecular-weight polysaccharides of different chemical compositions were obtained from cells of nine different wild-type strains of the phototrophic bacterium Rhodopseudomonas gelatinosa. The polysaccharides are free of typical capsule components like hexuronic or aminohexuronic acids but contain (except that of strain 39/2) substantial amounts of phosphorus. A number of unusual o-methyl sugars (2-o-methyl-D-galactose, 2,3-di-o-methyl-D-galactose, 2-o-methyl-L-fucose) as well as 3,6-dideoxy-D-xylo-hexose (abequose) were identified in the R. gelatinosa polysaccharides. o-Methyl and dideoxy sugars however, are typical constituents of O-specific chains of the lipopolysaccharides of gram-negative bacteria (Rhodospirillaceae and Enterobacteriaceae, respectively). Considering both the R-type character of the R. gelatinosa lipopolysaccharides and the occurrence of these strain-specific ETEROPOLYSACCHARIDES, THE ASSUMPTION SEEMS TO BE JUSTIFIED THAT THE LOW-MOLECULAR-WEIGHT POLYSACCHARIDES ARE RELATED TO O-specific chains of lipopolysaccharides (haptens) rather than to capsular or slime antigens. In serological terms the polysaccharides of R. gelatinosa have to be classified as K-antigens. They are able to cover the O-specificity of the respective different strains and confer on them additional specificity which is demonstrable by bacterial agglutination.