Department of Biochemistry, University of Wisconsin - Madison, Madison, Wisconsin, United States of America.
Department of Biological Sciences, Louisiana State University and A & M College, Baton Rouge, Louisiana, United States of America.
PLoS One. 2019 Jan 23;14(1):e0199482. doi: 10.1371/journal.pone.0199482. eCollection 2019.
We have previously generated four replicate populations of ionizing radiation (IR)-resistant Escherichia coli though directed evolution. Sequencing of isolates from these populations revealed that mutations affecting DNA repair (through DNA double-strand break repair and replication restart), ROS amelioration, and cell wall metabolism were prominent. Three mutations involved in DNA repair explained the IR resistance phenotype in one population, and similar DNA repair mutations were prominent in two others. The remaining population, IR-3-20, had no mutations in the key DNA repair proteins, suggesting that it had taken a different evolutionary path to IR resistance. Here, we present evidence that a variant of the anaerobic metabolism transcription factor FNR, unique to and isolated from population IR-3-20, plays a role in IR resistance. The F186I allele of FNR exhibits a diminished ability to activate transcription from FNR-activatable promoters, and furthermore reduces levels of intracellular ROS. The FNR F186I variant is apparently capable of enhancing resistance to IR under chronic irradiation conditions, but does not increase cell survival when exposed to acute irradiation. Our results underline the importance of dose rate on cell survival of IR exposure.
我们之前通过定向进化生成了四个复制的耐电离辐射（IR）大肠杆菌种群。对这些种群中分离株的测序表明，影响 DNA 修复（通过 DNA 双链断裂修复和复制启动）、ROS 缓解和细胞壁代谢的突变是突出的。三个参与 DNA 修复的突变解释了一个种群中的 IR 抗性表型，而另外两个种群中则存在类似的 DNA 修复突变。其余的种群 IR-3-20 没有关键 DNA 修复蛋白的突变，这表明它采取了不同的进化途径来抵抗 IR。在这里，我们提供的证据表明，一种独特的、从种群 IR-3-20 中分离出来的厌氧代谢转录因子 FNR 的变体，在 IR 抗性中起作用。FNR 的 F186I 等位基因表现出减弱激活 FNR 可激活启动子转录的能力，并且还降低了细胞内 ROS 的水平。FNR F186I 变体显然能够增强在慢性辐照条件下对 IR 的抗性，但在暴露于急性辐照时不会增加细胞存活率。我们的结果强调了剂量率对 IR 暴露细胞存活的重要性。
