Effectiveness of Rhizobium as modified by mutation for resistance to antibiotics.

Abstract

Many antibiotic-resistant mutants derived from effective strains ofRhizobium — mainlyR. leguminosarum andR. trifolii showed some loss of effectiveness on the homologous host. The frequency and degree of such changes in effectiveness depended on the type of antibiotic-resistance involved in the mutations. Resistance to streptomycin, spiramycin, chloramphenicol, or the tetracycline group of antibiotics was associated with little or no change. Resistance to D-cycloserine, novobiocin, vancomycin, bacitracin or penicillin was accompanied by partial or full loss of effectiveness in about one-half of the mutants. Full loss of effectiveness occurred most frequently among mutants selected for resistance to viomycin or neomycin. In contrast, restoration of the ability for effective symbiosis occurred in prototrophic revertants of a non-nodulating, purine-requiring mutant. Alteration of cell-wall characteristics is suggested as a possible basis for decrease of effectiveness among mutants resistant to those antibiotics, notablyD-cycloserine, which are known to inhibit cell-wall synthesis.