@article{mbs:/content/journal/micro/10.1099/00221287-68-2-199, author = "Williams, P. H. and Clarke, C. H.", title = "Pre- and Post-irradiation Effects upon Lethality and Reversion in Salmonella typhimurium", journal= "Microbiology", year = "1971", volume = "68", number = "2", pages = "199-205", doi = "https://doi.org/10.1099/00221287-68-2-199", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-68-2-199", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", abstract = "SUMMARY Lag, exponential and stationary phase cells of Salmonella typhimurium lt-2 (trpC3) grown in nutrient broth or tryptophan-supplemented minimal medium were irradiated with doses of u.v. up to 570 ergs/mm2. Casein hydrolysate supplementation of the post-irradiation plating medium causes enhanced survival only for lag and exponential phase broth-grown and exponential phase minimal- grown cells. Caffeine invariably leads to decreased survival levels and abolition of any casein hydrolysate enhancement of survival. Cells of all six growth conditions give induced Trp+ reversions, often due to suppressor mutations, on plating media containing casein hydrolysate. Only for minimal-grown lag and exponential phase cells do any induced Trp+ appear on media devoid of casein hydrolysate supplementation. In these cases too, caffeine has a definite antimutagenic action. Mutation frequency decline (MFD) experiments revealed that those cells exhibiting a casein hydrolysate enhancement of survival on plates also show a delayed onset of MFD and a fall of survival, after an initial delay, in liquid minimal medium. MFD experiments in liquid do not give a complete quantitative explanation for the Trp+ revertant yields found on plates. We suggest that intracellular free amino acid pool sizes may be a common factor in the correlations which we have observed.", }