Induction of SOS Genes by a Low Dose of Gamma Radiation, 10 Gy, in Salmonella enterica Serovar Typhimurium

In a previous study, a relatively high dose of gamma radiation (1 kGy) did not fully induce typical SOS genes such as sulA, recA, recN, and din in Salmonella Typhimurium (S. Typhimurium) (Lim et al. 2008, Gene expression profiles following high-dose exposure to gamma radiation in Salmonella enterica serovar Typhimuium. J. Radiat. Ind. 3:111-119). In this study, we examined changes in the transcriptional repertoire of S. Typhimurium after a dose of 10 Gy using DNA microarrays. It was found that more than half (~65%) of the 26 up-regulated genes belong to the SOS regulon: ten genes are typical SOS genes, and seven genes are Salmonella prophage genes, which are known to be activated by LexA cleavage. Among 29 down-regulated genes, the function of five genes with the most decreased expression is associated with carbohydrate transport and energy production. This suggests that upon exposure to gamma radiation cells may cease growing by reducing the metabolic activity, and repair DNA damage using a DNA repair system such as the SOS response system. The difference in expression of the SOS genes between a high (1 kGy) and low (10 Gy) dose of radiation shows the possibility that cells may opt for one of multiple regulatory circuits in response to the specific gamma radiation dose.