Escherichia coli Genes and Pathways Involved in Surviving Extreme Exposure to Ionizing Radiation

To further an improved understanding of the mechanisms used by bacterial cells to survive extreme exposure to ionizing radia-tion (IR), we broadly screened nonessential Escherichia coli genes for those involved in IR resistance by using transposon-di-rected insertion sequencing (TraDIS). Forty-six genes were identified, most of which become essential upon heavy IR exposure. Most of these were subjected to direct validation. The results reinforced the notion that survival after high doses of ionizing radi-ation does not depend on a single mechanism or process, but instead is multifaceted. Many identified genes affect either DNA repair or the cellular response to oxidative damage. However, contributions by genes involved in cell wall structure/function, cell division, and intermediary metabolism were also evident. About half of the identified genes have not previously been associated with IR resistance or recovery from IR exposure, including eight genes of unknown function. Organisms have evolved mechanisms to maintain genomic in-tegrity in the face of extreme environmental stresses. One class of extremophiles, typified by the bacterium Deinococcus radiodurans (1, 2), exhibits extraordinary resistance to the effects of high doses of ionizing radiation (IR). The repair of damaged DNA, stalled replication forks, and other damaged cellular com-ponents is critical for cells to survive exposure to IR. The DNA sugar-phosphate backbone is particularly susceptible to both di