Rachel & Menachem Mendelovitch Evolutionary Processes of Mutation & Natural Selection Research Laboratory, Department of Genetics and Developmental Biology, The Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel.
Department of Evolutionary and Environmental Biology and the Institute of Evolution, University of Haifa, Haifa, Israel.
Mol Biol Evol. 2021 Jun 25;38(7):2778-2790. doi: 10.1093/molbev/msab067.
Many bacterial species that cannot sporulate, such as the model bacterium Escherichia coli, can nevertheless survive for years, following exhaustion of external resources, in a state termed long-term stationary phase (LTSP). Here we describe the dynamics of E. coli adaptation during the first three years spent under LTSP. We show that during this time, E. coli continuously adapts genetically through the accumulation of mutations. For nonmutator clones, the majority of mutations accumulated appear to be adaptive under LTSP, reflected in an extremely convergent pattern of mutation accumulation. Despite the rapid and convergent manner in which populations adapt under LTSP, they continue to harbor extensive genetic variation. The dynamics of evolution of mutation rates under LTSP are particularly interesting. The emergence of mutators affects overall mutation accumulation rates as well as the mutational spectra and the ultimate spectrum of adaptive alleles acquired under LTSP. With time, mutators can evolve even higher mutation rates through the acquisition of additional mutation rate-enhancing mutations. Different mutator and nonmutator clones within a single population and time point can display extreme variation in their mutation rates, resulting in differences in both the dynamics of adaptation and their associated deleterious burdens. Despite these differences, clones that vary greatly in their mutation rates tend to coexist within their populations for many years, under LTSP.
许多不能形成孢子的细菌物种，如模式细菌大肠杆菌，在外部资源耗尽后，仍然可以在一种称为长期静止期（LTSP）的状态下存活数年。在这里，我们描述了大肠杆菌在 LTSP 下度过的头三年中适应的动态。我们表明，在此期间，大肠杆菌通过积累突变不断在遗传上进行适应。对于非突变体克隆，积累的大多数突变似乎在 LTSP 下具有适应性，这反映在突变积累的极其趋同模式中。尽管在 LTSP 下种群以快速和趋同的方式适应，但它们仍然具有广泛的遗传变异。LTSP 下突变率进化的动态特别有趣。突变体的出现不仅影响总体突变积累率，还影响 LTSP 下获得的突变谱和适应性等位基因的最终谱。随着时间的推移，突变体可以通过获得额外的增强突变率的突变而进化出更高的突变率。在单个种群和时间点内的不同突变体和非突变体克隆可能在其突变率上表现出极大的差异，从而导致适应的动态及其相关的有害负担的差异。尽管存在这些差异，但在 LTSP 下，在其种群中，突变率差异很大的克隆往往可以共存多年。
