Patterns of Reactivity between a Panel of Monoclonal Antibodies and Forage Rhizobium Strains

A panel of 11 monoclonal antibodies raised against vegetative cells of Rhizobium leguminosarum biovar trifolii or Rhizobium meliloti was tested by enzyme-linked immunosorbent assay for reactivity with 47 strains of R. leguminosarum biovar trifolii and 60 strains of R. meliloti. The goal of the study was to define the degree of specificity associated with each antibody and to gain an understanding of the amount of antigenic diversity found among the strains and between the species. Each antibody was tested against each Rhizobium strain in four forms: washed steamed cells, washed unsteamed cells, cell-free culture broth, and nodule squash material. Each antibody showed a different pattern of reactivity among the 107 strains. One of each of the antibodies developed against R. meliloti and R. leguminosarum biovar trifolii reacted in a highly specific manner with cells or antigen from the immunogenic strain only. Nine of the antibodies recognized secreted as well as cellular antigen from many of the strains. Analysis of patterns of reactivity between the 107 strains and the 11 antibodies separated the strains into 28 groups of which 12 were represented by one strain only.