Radiation resistance comparable to natural extremophiles achieved through experimental evolution

Recent human exploitation of high-level sources of ionizing radiation (IR) has generated a corresponding need to understand the effects of IR on living systems. Part of that research has focused on the astonishing capacity of some organisms to survive extraordinary levels of IR exposure. Using experimental evolution, we have generated populations of Escherichia coli with an IR resistance phenotype comparable to the extremophile Deinococcus radiodurans. Every aspect of cell physiology is affected. Cellular isolates exhibit approximately 1,000 base pair changes plus major genomic and proteomic alterations. The extreme IR resistance phenotype, stable without selection for at least 100 generations, has no single molecular origin. Defined and probable contributions include alterations in cellular systems involved in DNA repair, amelioration of reactive oxygen species, Fe metabolism and repair of iron-sulfur centers, DNA packaging, intermediary metabolism, and more. Some contributions to IR resistance are highly dependent on both genomic and environmental context.