Physiological states can determine the ability of organisms to handle stress. Does this mean that the same selection pressure will lead to different evolutionary outcomes, depending on the organisms' physiological state? If yes, what will be the genomic signatures of such adaptation(s)? We used experimental evolution in Escherichia coli followed by whole-genome whole-population sequencing to investigate these questions. The sensitivity of Escherichia coli to ultraviolet (UV) radiation depends on the growth phase during which it experiences the radiation. We evolved replicate E. coli populations under two different conditions of UV exposures, namely exposure during the lag and the exponential growth phases. Initially, the UV sensitivity of the ancestor was greater during the exponential phase than the lag phase. However, at the end of 100 cycles of exposure, UV resistance evolved to similar extents in both treatments. Genome analysis showed that mutations in genes involved in DNA repair, cell membrane structure and RNA polymerase were common in both treatments. However, different functional groups were found mutated in populations experiencing lag and exponential UV treatment. In the former, genes involved in transcriptional and translational regulations and cellular transport were mutated, whereas the latter treatment showed mutations in genes involved in signal transduction and cell adhesion. Interestingly, the treatments showed no phenotypic differences in a number of novel environments. Taken together, these results suggest that selection pressures at different physiological stages can lead to differences in the genomic signatures of adaptation, which need not necessarily translate into observable phenotypic differences.

中文翻译：

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大肠杆菌抗紫外线进化的基因组特征取决于暴露期间的生长阶段。

生理状态可以决定生物体处理压力的能力。这是否意味着相同的选择压力会导致不同的进化结果，取决于生物体的生理状态？如果是，这种适应的基因组特征是什么？我们在大肠杆菌中使用实验进化，然后进行全基因组全种群测序来研究这些问题。大肠杆菌对紫外线 (UV) 辐射的敏感性取决于它经历辐射的生长阶段。我们在两种不同的紫外线照射条件下进化了复制大肠杆菌种群，即在滞后和指数生长阶段的暴露。最初，祖先的紫外线敏感性在指数阶段比滞后阶段更大。然而，在 100 次暴露循环结束时，两种处理的抗紫外线能力发展程度相似。基因组分析表明，参与 DNA 修复、细胞膜结构和 RNA 聚合酶的基因突变在两种治疗中都很常见。然而，在经历滞后和指数紫外线处理的人群中发现不同的官能团发生了突变。在前者中，参与转录和翻译调控以及细胞转运的基因发生了突变，而后者的处理显示了参与信号转导和细胞粘附的基因发生了突变。有趣的是，这些处理在许多新环境中没有表现出表型差异。总之，这些结果表明，不同生理阶段的选择压力会导致适应基因组特征的差异，