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J Bacteriol. 1973 January; 113(1): 133-144
Copyright © 1973 American Society for Microbiology. All Rights Reserved.

Radiation-Resistant Mutants of Salmonella typhimurium LT2: Development and Characterization¹

^a Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

ABSTRACT

A series of repeated exposures to gamma irradiation with intervening outgrowth of survivors was used to develop radioresistant cultures of Salmonella typhimuium LT2. Stepwise increases in resistance to both ionizing and ultraviolet irradiation were obtained independently of the presence or absence of integrated P22 prophage. Single clonal isolates, representing parent and radioresistant populations, retained the general characteristics of the LT2 parent, including serological properties, phage typing, antibiotic sensitivities, mouse virulence, and most biochemical test reactions. Resistant cells were generally larger and contained 1.8 to 2.1 times more ribonucleic acid and protein than parent cells, but deoxyribonucleic acid (DNA) contents were similar. Heterogeneity in the populations with respect to release of H₂S, utilization of carbon sources, and growth on minimal medium is considered to be ancillary, rather than causally related, to increased radioresistance. The resistant isolates displayed an increased ability to reactivate gamma-irradiated P22 phage. DNA polymerase I and polynucleotide-joining enzyme activities were elevated in extracts of radioresistant cells relative to parent cells. It is suggested that the observed increases in radioresistance result from a selection of mutations leading to an increased capacity to repair DNA.

² Present address: National College of Food Technology, University of Reading, Weybridge, Surrey, England.

¹ Contribution No. 1993 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge.

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