Immunochemistry of newly found substituents of polysaccharides of Rhizobium species.

Acetyl and pyruvic acid groups were detected and estimated in the extracellular polysaccharides of Rhizobium trifolii and R. meliloti. Pyruvic acid was found also in the specific polysaccharide of pneumococcal type 27, and is believed to explain the cross-reactivity between antiserum to pneumococcal type 27 and these and other pyruvate-containing bacterial polysaccharides. Removal of pyruvate from a Rhizobium polysaccharide rendered it inactive with its homologous antiserum and with antiserum to pneumococcal type 27, but it then reacted with several antiserums to other pneumococcal types with which the intact material was unreactive.