A Serological Study of Root Nodule Bacteria from Pea and Clover Inoculation Groups

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Abstract
29 strains of nodule bacteria derived from plants of the pea inoculation group, and 161 strains derived from clover nodules, were tested for agglutination with antisera against 6 strains of nodule bacteria, 4 derived from clover and 2 from peas. No antigen or set of antigens of either O or H type was found to be common to the whole group. Some strains reacted with none of the antisera, some with only 1, and others with several antisera, but none with all of them. Strains belonging to both inoculation groups were found to give agglutination with 5 of the antisera; 1 antiserum reacted only with a small number of strains all from clover. Neither ability to cross-inoculate between clover and pea host plants, nor effectiveness in fixing N within the host plant, nor susceptibility to a bacteriophage was necessarily associated with the presence or absence of any one antigen or group of antigens. Indeed, an effective strain and a very ineffective variant derived from it were found to be serologically identical. There was, however, a partial correlation between effectiveness and the H antigenic constitution.