Ionizing radiation (IR) is lethal to most organisms at high doses, damaging every cellular macromolecule via induction of reactive oxygen species (ROS). Utilizing experimental evolution and continuing previous work, we have generated the most IR-resistant Escherichia coli populations developed to date. After 100 cycles of selection, the dose required to kill 99% the four replicate populations (IR9-100, IR10-100, IR11-100, and IR12-100) has increased from 750 Gy to approximately 3,000 Gy. Fitness trade-offs, specialization, and clonal interference are evident. Long-lived competing sub-populations are present in three of the four lineages. In IR9, one lineage accumulates the heme precursor, porphyrin, leading to generation of yellow-brown colonies. Major genomic alterations are present. IR9 and IR10 exhibit major deletions and/or duplications proximal to the chromosome replication terminus. Contributions to IR resistance have expanded beyond the alterations in DNA repair systems documented previously. Variants of proteins involved in ATP synthesis (AtpA), iron-sulfur cluster biogenesis (SufD) and cadaverine synthesis (CadA) each contribute to IR resistance in IR9-100. Major genomic and physiological changes are emerging. An isolate from IR10 exhibits protein protection from ROS similar to the extremely radiation resistant bacterium Deinococcus radiodurans, without evident changes in cellular metal homeostasis. Selection is continuing with no limit to IR resistance in evidence as our E. coli populations approach levels of IR resistance typical of D. radiodurans.

高剂量的电离辐射（IR）对大多数生物都是致命的，通过诱导活性氧（ROS）破坏每个细胞大分子。利用实验发展和继续的先前工作，我们产生了最耐红外的大肠杆菌迄今已发展出种群。经过100个选择周期，杀死99％的四个重复种群（IR9-100，IR10-100，IR11-100和IR12-100）所需的剂量已从750 Gy增加到大约3,000 Gy。健身的权衡，专业化和克隆干扰是显而易见的。四个谱系中的三个存在长寿的竞争亚群。在IR9中，一个血统会积累血红素前体卟啉，导致生成黄棕色菌落。存在主要的基因组改变。IR9和IR10在染色体复制末端附近表现出主要的缺失和/或重复。对红外抗性的贡献已超出了先前记录的DNA修复系统的变化。ATP合成（AtpA）中涉及的蛋白质变体，铁硫团簇生物发生（SufD）和尸胺合成（CadA）各自对IR9-100的IR抗性产生影响。主要的基因组和生理变化正在出现。与极端抗辐射细菌相似，IR10的分离物对ROS具有蛋白质保护作用放射球菌，而细胞金属稳态没有明显变化。选择正在进行中，对IR的抵抗力不受限制大肠杆菌 人群接近典型的IR抵抗水平 D. radiodurans。