School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Leibniz Institute of Polymer Research and the Max Bergmann Center of Biomaterials, 01069 Dresden, Germany.
Nat Microbiol. 2017 Jul 24;2:17115. doi: 10.1038/nmicrobiol.2017.115.
The shapes of most bacteria are imparted by the structures of their peptidoglycan cell walls, which are determined by many dynamic processes that can be described on various length scales ranging from short-range glycan insertions to cellular-scale elasticity. Understanding the mechanisms that maintain stable, rod-like morphologies in certain bacteria has proved to be challenging due to an incomplete understanding of the feedback between growth and the elastic and geometric properties of the cell wall. Here, we probe the effects of mechanical strain on cell shape by modelling the mechanical strains caused by bending and differential growth of the cell wall. We show that the spatial coupling of growth to regions of high mechanical strain can explain the plastic response of cells to bending and quantitatively predict the rate at which bent cells straighten. By growing filamentous Escherichia coli cells in doughnut-shaped microchambers, we find that the cells recovered their straight, native rod-shaped morphologies when released from captivity at a rate consistent with the theoretical prediction. We then measure the localization of MreB, an actin homologue crucial to cell wall synthesis, inside confinement and during the straightening process, and find that it cannot explain the plastic response to bending or the observed straightening rate. Our results implicate mechanical strain sensing, implemented by components of the elongasome yet to be fully characterized, as an important component of robust shape regulation in E. coli.
大多数细菌的形状是由其肽聚糖细胞壁的结构决定的，这些结构由许多动态过程决定，可以在从短程聚糖插入到细胞尺度弹性的各种长度尺度上进行描述。由于对生长与细胞壁的弹性和几何性质之间的反馈关系理解不完整，因此，理解某些细菌中保持稳定、杆状形态的机制一直具有挑战性。在这里，我们通过模拟细胞壁弯曲和差异生长引起的机械应变来研究机械应变对细胞形状的影响。我们表明，生长与高机械应变区域的空间耦合可以解释细胞对弯曲的塑性响应，并定量预测弯曲细胞变直的速度。通过在甜甜圈形微室中培养丝状大肠杆菌细胞，我们发现当细胞从囚禁中释放出来时，以与理论预测一致的速度恢复其直的、天然的杆状形态。然后，我们测量了在限制内和变直过程中对细胞壁合成至关重要的肌动蛋白同源物 MreB 的定位，发现它不能解释对弯曲的塑性响应或观察到的变直速度。我们的结果表明，机械应变感应，由尚未完全表征的伸长体组件来执行，是大肠杆菌中稳健形状调节的重要组成部分。
