Somatic serogroups among 55 strains of Rhizobium phaseoli

Abstract

The serological relationships among 55 strains of Rhizobium phaseoli of diverse geographical origin were examined by direct immunofluorescence. Five clear-cut serogroups and a minimum of 11 somatic antigenic determinants were detected among 42 strains using 11 fluorescent antibodies. At least a sixth serogroup exists to account for the remaining 13 unreactive strains. Serogroups 1 and 2 comprised a large number of strains (15 and 21, respectively), whereas serogroup 3 comprised only 4 strains and serogroups 4 and 5 a single strain each. These findings attest to a high degree of antigenic diversity as well as a high incidence of certain antigenic determinants in the collection of R. phaseoli examined. As a consequence, choice candidates for ecological studies would be strains endowed with a distinctive antigenic make-up as in serogroups 4 and 5.