REL 1206 Reference Genome

To estimate the number and diversity of beneficial mutations, we experimentally evolved 115 populations of Escherichia coli to 42.2°C for 2000 generations and sequenced one genome from each population. We identified 1331 total mutations, affecting more than 600 different sites. Few mutations were shared among replicates, but a strong pattern of convergence emerged at the level of genes, operons, and functional complexes. Our experiment uncovered a set of primary functional targets of high temperature, but we estimate that many other beneficial mutations could contribute to similar adaptive outcomes. We inferred the pervasive presence of epistasis among beneficial mutations, which shaped adaptive trajectories into at least two distinct pathways involving mutations either in the RNA polymerase complex or the termination factor rho.

为估算有益突变的数量与多样性，我们通过实验将115株大肠杆菌（Escherichia coli）种群在42.2℃的环境下传代进化2000代，并对每个种群的单份基因组进行测序。本研究共鉴定出1331个突变，涉及超过600个不同的基因组位点。尽管重复实验间共享的突变极少，但在基因、操纵子（operons）以及功能复合物层面，呈现出显著的趋同演化模式。本实验揭示了一组高温适应的核心功能靶点，但我们估算仍有大量其他有益突变可促成类似的适应性演化结果。我们推断有益突变间广泛存在上位性（epistasis），这种互作将适应性演化路径划分为至少两条截然不同的通路：一条涉及RNA聚合酶复合物（RNA polymerase complex）的突变，另一条则与终止因子rho（termination factor rho）相关。