All organisms encode enzymes that replicate, maintain, pack, recombine, and repair their genetic material. For this reason, mutation rates and biases also evolve by mutation, variation, and natural selection. By examining metagenomic time series of the Lenski long-term evolution experiment (LTEE) with Escherichia coli (Good, et al. 2017), we find that local mutation rate variation has evolved during the LTEE. Each LTEE population has evolved idiosyncratic differences in their rates of point mutations, indels, and mobile element insertions, due to the fixation of various hypermutator and antimutator alleles. One LTEE population, called Ara+3, shows a strong, symmetric wave pattern in its density of point mutations, radiating from the origin of replication. This pattern is largely missing from the other LTEE populations, most of which evolved missense, indel, or structural mutations in topA, fis, and dusB— loci that all affect DNA topology. The distribution of mutations in those genes over time suggests epistasis and historical contingency in the evolution of DNA topology, which may have in turn affected local mutation rates. Overall, the replicate populations of the LTEE have largely diverged in their mutation rates and biases, even though they have adapted to identical abiotic conditions.

中文翻译：

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在大肠杆菌的长期进化实验中，突变率和偏倚的发散进化。

所有生物都编码可复制，维持，包装，重组和修复其遗传物质的酶。因此，突变率和偏倚也会因突变，变异和自然选择而演变。通过检查Lenski长期进化实验（LTEE）与大肠杆菌的宏基因组时间序列（Good等人，2017），我们发现在LTEE期间局部突变率变化已经演变。由于固定了各种高变和反变等位基因，每个LTEE群体在点突变，插入缺失和移动元件插入的速率上都发生了特异的差异。一个称为Ara + 3的LTEE群体在其点突变密度中表现出强烈的对称波型，从复制起点辐射而来。这种模式在很大程度上与其它种群LTEE，其中大部分在进化错义，插入缺失，或结构的突变缺失TOPA，FIS和DUSB—全部影响DNA拓扑的基因座。这些基因中的突变随时间的分布表明DNA拓扑结构演变中的上位性和历史偶然性，这可能反过来又影响了局部突变率。总体而言，LTEE的重复种群在突变率和偏倚方面存在很大差异，即使它们已适应相同的非生物条件。