Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
Department of Bioengineering, Stanford University, Stanford, CA 94305, USA; Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Curr Opin Microbiol. 2018 Apr;42:62-70. doi: 10.1016/j.mib.2017.10.015. Epub 2017 Nov 7.
Rapid changes in environmental osmolarity are a natural aspect of microbial lifestyles. The change in turgor pressure resulting from an osmotic shock alters the mechanical forces within the cell envelope, and can impact cell growth across a range of timescales, through a variety of mechanical mechanisms. Here, we first summarize measurements of turgor pressure in various organisms. We then review how the combination of microfluidic flow cells and quantitative image analysis has driven discovery of the diverse ways in which turgor pressure mechanically regulates bacterial growth, independent of the effect of cytoplasmic crowding. In Gram-positive, rod-shaped bacteria, reductions in turgor pressure cause decreased growth rate. Moreover, a hypoosmotic shock, which increases turgor pressure and membrane tension, leads to transient inhibition of cell-wall growth via electrical depolarization. By contrast, Gram-negative Escherichia coli is remarkably insensitive to changes in turgor. We discuss the extent to which turgor pressure impacts processes such as cell division that alter cell shape, in particular that turgor facilitates millisecond-scale daughter-cell separation in many Actinobacteria and eukaryotic fission yeast. This diverse set of responses showcases the potential for using osmotic shocks to interrogate how mechanical perturbations affect cellular processes.
快速变化的环境渗透压是微生物生活方式的一个自然方面。渗透压冲击导致的膨压变化改变了细胞包膜内的机械力，并通过多种机械机制在各种时间尺度上影响细胞生长。在这里，我们首先总结了各种生物中膨压的测量方法。然后，我们回顾了微流控流动细胞与定量图像分析的结合如何推动了对渗透压机械调节细菌生长的多种方式的发现，而这些方式与细胞质拥挤的影响无关。在革兰氏阳性、杆状细菌中，膨压的降低会导致生长速度减慢。此外，低渗冲击会增加膨压和膜张力，通过去极化导致细胞壁生长的短暂抑制。相比之下，革兰氏阴性的大肠杆菌对膨压的变化非常不敏感。我们讨论了膨压在改变细胞形状的过程（如细胞分裂）中的影响程度，特别是膨压促进了许多放线菌和真核裂殖酵母中毫秒级别的子细胞分离。这一系列不同的反应展示了利用渗透压冲击来探究机械扰动如何影响细胞过程的潜力。
