Bacterial Evolution in High-Osmolarity Environments
Bacterial Evolution in High-Osmolarity Environments
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DOI：
10.1128/mbio.01191-20
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发表时间：
2020-07-01
期刊：
影响因子：
6.4
通讯作者：
Huang, Kerwyn Casey
中科院分区：
文献类型：
--
作者：
Cesar, Spencer;Anjur-Dietrich, Maya;Huang, Kerwyn Casey
细菌必须保持高于环境的细胞质渗透压才能吸收水分。因此，高渗透压环境给细菌带来了巨大的压力。为了探索细菌适应高渗透压环境的进化机制，我们选择了含有各种渗透剂和浓度的培养基中的大肠杆菌 250 代。适应是渗透压依赖性的，山梨醇应激通常导致在较高渗透压条件下适应性增加，而高浓度脯氨酸的选择导致特别针对脯氨酸的适应性增加。与这些表型一致，进化群体的测序表明，脯氨酸的传代导致相关代谢途径中的特定突变，增加了利用脯氨酸生长的能力，而山梨醇的进化导致许多不同基因的突变，通常导致高渗透压条件下的生长改善，但以低渗透压下的生长为代价。与以脯氨酸作为唯一碳源的生长相比，高渗透压降低了生长速率，但增加了平均细胞体积，这表明渗透压诱导的生长速率和细胞大小的变化遵循与细胞大小和营养质量相关的经典生长定律的正交关系。来自山梨醇进化群体的分离物捕获了宏基因组测序揭示的可能的突变时间序列，证明了高渗透压生长和低渗透压生长之间的权衡。我们的报告强调了实验进化在剖析复杂细胞网络和环境相互作用方面的实用性，特别是在涉及特定和一般代谢应激源的行为的情况下。重要性对于细菌来说，保持比环境中更高的内部溶质浓度可以使细胞吸收水分。因此，在高渗透压环境中生存具有挑战性。为了研究细菌如何适应高渗透压环境，我们将大肠杆菌保存在各种高渗透压溶液中数百代。我们发现，进化的种群根据渗透传代条件采取不同的策略来提高其生长速度，要么普遍适应高渗透压条件，要么更好地代谢渗透物作为碳源。单细胞成像表明，增强的适应性与更快的生长有关，宏基因组测序揭示了反映不同渗透压生长权衡的突变。我们的研究证明了长期进化实验对于探索环境压力期间发生的适应的实用性。
Bacteria must maintain a cytosolic osmolarity higher than that of their environment in order to take up water. High-osmolarity environments therefore present formidable stress to bacteria. To explore the evolutionary mechanisms by which bacteria adapt to high-osmolarity environments, we selected Escherichia coli in media with a variety of osmolytes and concentrations for 250 generations. Adaptation was osmolyte dependent, with sorbitol stress generally resulting in increased fitness under conditions with higher osmolarity, while selection in high concentrations of proline resulted in increased fitness specifically on proline. Consistent with these phenotypes, sequencing of the evolved populations showed that passaging in proline resulted in specific mutations in an associated metabolic pathway that increased the ability to utilize proline for growth, while evolution in sorbitol resulted in mutations in many different genes that generally resulted in improved growth under high-osmolarity conditions at the expense of growth at low osmolarity. High osmolarity decreased the growth rate but increased the mean cell volume compared with growth on proline as the sole carbon source, demonstrating that osmolarityinduced changes in growth rate and cell size follow an orthogonal relationship from the classical Growth Law relating cell size and nutrient quality. Isolates from a sorbitol-evolved population that captured the likely temporal sequence of mutations revealed by metagenomic sequencing demonstrated a trade-off between growth at high osmolarity and growth at low osmolarity. Our report highlights the utility of experimental evolution for dissecting complex cellular networks and environmental interactions, particularly in the case of behaviors that can involve both specific and general metabolic stressors.IMPORTANCE For bacteria, maintaining higher internal solute concentrations than those present in the environment allows cells to take up water. As a result, survival is challenging in high-osmolarity environments. To investigate how bacteria adapt to high-osmolarity environments, we maintained Escherichia coli in a variety of high-osmolarity solutions for hundreds of generations. We found that the evolved populations adopted different strategies to improve their growth rates depending on the osmotic passaging condition, either generally adapting to high-osmolarity conditions or better metabolizing the osmolyte as a carbon source. Single-cell imaging demonstrated that enhanced fitness was coupled to faster growth, and metagenomic sequencing revealed mutations that reflected growth trade-offs across osmolarities. Our study demonstrated the utility of long-term evolution experiments for probing adaptation occurring during environmental stress.