Symbiotic Properties of Antibiotic-Resistant and Auxotrophic Mutants of Rhizobium leguminosarum

A number of auxotrophic and antibiotic-resistant mutants of Rhizobium leguminosarum were isolated and their symbiotic properties examined. Among the auxotrophic mutants tested, only those with an adenine requirement were found to be symbiotically defective and these were all non-infective. Of the antibiotic-resistant mutants isolated, only a minority of the rifampicin-resistant mutants had a modified symbiotic phenotype and this was ineffective. Preliminary evidence suggests that the basis for the resistance in these mutants is a modified DNA-dependent RNA polymerase.