RADIATION-SENSITIVE AND RECOMBINATIONLESS MUTANTS OF SALMONELLA-TYPHIMURIUM

Mutants of S. typhimurium sensitive to UV light fall into several categories. In addition to quantitative UV differences, some are sensitive to X-ray and chemical mutagens, some are unable to repair damage to irradiated phage (hcr), some are recombinationless (rec) and, after lysogenization, some cannot be induced to produce mature phage. More than 60 radiation-sensitive mutants have been collected and classified as to phenotypes. X-ray sensitive mutants were tested for sensitivity to nitrosoguanidine and, as yet, no case has been found where the two phenotypes are separable. If the mechanism of repair of damage by the two agents is identical, the use of nitrosoguanidine would be extremely helpful for inactivation measurements and in screening procedures, especially in those laboratories where X-ray equipment is not readily available. A simplified method for scoring inducibility was developed based upon the knowledge that S. typhimurium is naturally lysogenic. The rec mutants have pleiotropic properties, but these are probably due to a single mutation, since all properties became wild-type upon reversion or recombination. Among the pleiotropic properties of rec is the exhibition of liquid-holding recovery, a characteristic not seen in most of the other radiation-sensitive mutants. 3 of the radiation-sensitive mutants were found by testing appropriate auxotrophs in our collection, without any selection procedure involving exposure to radiation. © 1969.