Changes in Cell Size and Shape during 50,000 Generations of Experimental Evolution with Escherichia coli
Changes in Cell Size and Shape during 50,000 Generations of Experimental Evolution with Escherichia coli
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DOI：
10.1128/jb.00469-20
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发表时间：
2021-05-01
影响因子：
3.2
通讯作者：
Lenski, Richard E.
中科院分区：
文献类型：
--
作者：
Grant, Nkrumah A.;Magid, Ali Abdel;Lenski, Richard E.
细菌具有多种大小和形状，许多物种表现出典型的形态。形态如何变化以及在什么时间尺度上变化尚不清楚。之前在大肠杆菌实验中检查细胞形态的工作表明，群体进化出更大的细胞，在某些情况下，细胞的棒状程度较低。该实验现已进行了二十多年。同时，这些群体的基因组序列数据是可用的，新的计算方法可以实现高通量微观分析。在这项研究中，我们测量了祖先和 12 个群体在 2,000、10,000 和 50,000 代的稳定期细胞体积，包括最后一个时间点指数生长期间的测量。我们使用库尔特计数器和显微镜测量了每个样品的细胞体积分布，后者还提供了细胞形状的数据。我们的数据证实了细胞变大的趋势，同时也揭示了复制群体之间大小和形状的巨大差异。大多数种群首先进化出更宽的细胞，但后来又恢复到祖先的长宽比。除了一个种群外，所有种群都进化出了杆状维持基因的突变。我们还在唯一进化出在柠檬酸盐上生长的新能力的群体中观察到许多幽灵状细胞，支持了该谱系难以维持平衡生长的假设。最后，我们发现细胞大小和适应度在 50,000 代中仍然保持相关性。我们的结果表明，较大的细胞在实验环境中是有益的，而向祖先长宽比的回归表明对进化细胞不太有利的表面积与体积比的部分补偿。重要性细菌表现出巨大的形态多样性，但我们对它们的细胞大小和形状如何进化以及这些特征如何影响生物体适应性的了解有限。这种知识差距部分反映了细菌化石记录的缺乏。在这项研究中，我们复活并分析了来自 12 个实验进化大肠杆菌群体的 50,000 代以上的样本，以研究细胞大小、形状和适应性之间的关系。利用这种“冰冻化石记录”，我们发现所有 12 个种群都进化出了更大的细胞，同时适应性增强，并且复制系中的细胞大小和形状存在显着的异质性。我们的工作表明，即使在生活在相同环境中的群体中，细胞形态也很容易进化和多样化。
Bacteria adopt a wide variety of sizes and shapes, with many species exhibiting stereotypical morphologies. How morphology changes, and over what timescales, is less clear. Previous work examining cell morphology in an experiment with Escherichia coli showed that populations evolved larger cells and, in some cases, cells that were less rod-like. That experiment has now run for over two more decades. Meanwhile, genome sequence data are available for these populations, and new computational methods enable high-throughput microscopic analyses. In this study, we measured stationary-phase cell volumes for the ancestor and 12 populations at 2,000, 10,000, and 50,000 generations, including measurements during exponential growth at the last time point. We measured the distribution of cell volumes for each sample using a Coulter counter and microscopy, the latter of which also provided data on cell shape. Our data confirm the trend toward larger cells while also revealing substantial variation in size and shape across replicate populations. Most populations first evolved wider cells but later reverted to the ancestral length-to-width ratio. All but one population evolved mutations in rod shape maintenance genes. We also observed many ghost-like cells in the only population that evolved the novel ability to grow on citrate, supporting the hypothesis that this lineage struggles with maintaining balanced growth. Lastly, we show that cell size and fitness remain correlated across 50,000 generations. Our results suggest that larger cells are beneficial in the experimental environment, while the reversion toward ancestral length-to-width ratios suggests partial compensation for the less favorable surface area-to-volume ratios of the evolved cells.IMPORTANCE Bacteria exhibit great morphological diversity, yet we have only a limited understanding of how their cell sizes and shapes evolve and of how these features affect organismal fitness. This knowledge gap reflects, in part, the paucity of the fossil record for bacteria. In this study, we revived and analyzed samples extending over 50,000 generations from 12 populations of experimentally evolving Escherichia coli to investigate the relation between cell size, shape, and fitness. Using this "frozen fossil record," we show that all 12 populations evolved larger cells concomitant with increased fitness, with substantial heterogeneity in cell size and shape across the replicate lines. Our work demonstrates that cell morphology can readily evolve and diversify, even among populations living in identical environments.