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Appl Environ Microbiol. 1961 September; 9(5): 410-414

Studies on Induced Variation in the Rhizobia

II. Radiation Sensitivity and Induction of Antibiotic-resistance Markers

Biology Department, Brookhaven National Laboratory, Upton, New York

ABSTRACT

The relation between survival and dose of ultraviolet (UV) light or X rays was, with only one exception, nonlinear for late-log-phase cultures of four species of Rhizobium. The LD₉₀ for different bacterial strains ranged from 400 to 3,000 ergs per mm² for UV treatment, and from 3.0 to 7.5 kr for X-ray treatment.

Minor existing differences in response to some antibacterial compounds (disc tests) were usable as secondary markers for genetic experiments. Spontaneous and radiation-induced mutants, resistant to high levels of several antibiotics, notably dihydrostreptomycin and erythromycin, were isolated for primary marker purposes. A significant phenotypic lag for mutation to dihydrostreptomycin resistance was noted for UV-irradiated cells. The UV-induced frequency exceeded the X-ray-induced frequency by a factor of at least three, at a comparable level of lethality. No significant change in the symbiotic capability was observed in rhizobial strains marked with antibiotics resistance.