Investigations upon the Antigenic Relationships among the Root-Nodule Bacteria of the Soybean, Cowpea, and Lupine Cross-Inoculation Groups.

Although several workers have investigated the serological characteristics of the organisms in the genus Rhizobium, few have given much consideration to the possible relationships between bacteria isolated from plants of the soybean, cowpea, and lupine groups. Moreover, none of these workers has had the benefit of recent discoveries in immunology, which have made new concepts and new techniques available for studies of the antigenic constitution of bacteria. The frequency with which recent papers (Leonard, 1923; Sears and Carroll, 1927; Hansen and Tanner, 1931; Carroll, 1934; Walker and Brown, 1935; Raju, 1936; Reid, 1936; Conklin, 1936; Toxopeus, 1936; Bushnell and Sarles, 1937) have reported "inter-crossings" among the bacteria and plants of the soybean, cowpea, and lupine groups, and the consequent confusion attending upon the classification of both plants and bacteria in these groups, has made advisable some study of the antigenic constituents of these bacteria. Such a study must necessarily consider the roles played by flagellar and by capsular substances in determining the serological specificity of a bacterial strain. The agglutination test appeared to lend itself best to a study of this sort.