Immunochemical analysis of O-specific polysaccharides from the soil nitrogen-fixing bacterium Azospirillum brasilense

Immunochemical reactivity of O-specific polysaccharide and the monosacchari de composition of O-antigenic determinants of the lipopolysaccharide isolat ed from the type strain Sp7 of Azospirillum brasilense were studied. An ori ginal modification of the method of spectroturbidimetry for disperse biolog ical systems and a nonstandard procedure for the preparation of monospecifi c antibodies against cell surface antigens were used. The polysaccharide fr action, which contained residues of galactose, rhamnose, and galacturonic a cid, was able to bind about 50% of the antibodies raised against whole bact erial cells. Twelve immunodeterminant groups were shown to be present in it s molecule. Galactose and, less effectively, rhamnose but not galacturonic acid inhibited the antigen-antibody reactions. It is concluded that the ser otype of the strain studied is determined by galactose residues.