Production and Use of Monoclonal Antibodies for Identification of Strains of Rhizobium trifolii.

We produced a monoclonal antibody against Rhizobium trifolii 162x95. This antibody in cell culture supernatant was used in an indirect enzyme-linked immunosorbent assay to differentiate strain 162x95 from naturalized strains in the Appalachian region. Nodules crushed in 0.1 to 0.2 ml of phosphate-buffered saline and used to charge enzyme-linked immunosorbent assay plates gave strong absorbance readings. Heat-inactivated and noninactivated portions of 162x95 cultures were strongly reactive, indicating that the antigen is probably a carbohydrate. Of 10 strains from California, where 162x95 was isolated, 6 strongly cross-reacted with the antibody. The cellular protein patterns in a sodium dodecyl sulfate-polyacrylamide gradient gel of cross-reactive strains were essentially identical. A Western blot analysis indicated that the antibody was against a 19.8-kilodalton band. The Western blot analysis also revealed that the polyvalent antiserum contained other strongly reacting antibodies with molecular weights of approximately 20,000, indicating the possibility that other monoclonal antibodies to detect strain 162x95 may be produced. However, the available antibody has been shown to be useful for short-term experiments. Based upon protein profiles and immunological reactions, there are 4 or 5 California strains rather than 10.