Hyperosmotic Shock Transiently Accelerates Constriction Rate in Escherichia coli.

Jiawei Sun,Handuo Shi,Kerwyn Casey Huang

doi:10.3389/fmicb.2021.718600

Jiawei Sun, Handuo Shi + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2021.718600

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Abstract

Bacterial cells in their natural environments encounter rapid and large changes in external osmolality. For instance, enteric bacteria such as Escherichia coli experience a rapid decrease when they exit from host intestines. Changes in osmolality alter the mechanical load on the cell envelope, and previous studies have shown that large osmotic shocks can slow down bacterial growth and impact cytoplasmic diffusion. However, it remains unclear how cells maintain envelope integrity and regulate envelope synthesis in response to osmotic shocks. In this study, we developed an agarose pad-based protocol to assay envelope stiffness by measuring population-averaged cell length before and after a hyperosmotic shock. Pad-based measurements exhibited an apparently larger length change compared with single-cell dynamics in a microfluidic device, which we found was quantitatively explained by a transient increase in division rate after the shock. Inhibiting cell division led to consistent measurements between agarose pad-based and microfluidic measurements. Directly after hyperosmotic shock, FtsZ concentration and Z-ring intensity increased, and the rate of septum constriction increased. These findings establish an agarose pad-based protocol for quantifying cell envelope stiffness, and demonstrate that mechanical perturbations can have profound effects on bacterial physiology.

Highlights

The bacterial cytoplasm contains a dense combination of nucleic acids, proteins, and numerous metabolites that together generate a high internal osmotic pressure relative to the extracellular environment
We carried out similar experiments and observed similar cell wall mechanical strains using the wall dye wheat germ agglutinin conjugated to AlexaFluor 488 (WGA-AF488) (Ursell et al, 2014) upon hyperosmotic shock and detergent treatment (Figures 1B,C); unshocked cell walls were extended by 9.6% relative to shocked cells, with a larger contraction upon lysis (Figure 1D)
While tracking of cells within the microfluidic device allowed us to measure the relative length change of each cell throughout the hyperosmotic shock and subsequent outer membrane (OM) destabilization, we found that the plasmolysis strain could be accurately quantified based on the population-averaged length before and after each treatment (Figure 1E)

Summary

Introduction

The bacterial cytoplasm contains a dense combination of nucleic acids, proteins, and numerous metabolites that together generate a high internal osmotic pressure relative to the extracellular environment. These turgor pressures of ∼1–10 atm (Cayley et al, 2000; Deng et al, 2011) must be balanced to maintain cellular integrity. To counter this mechanical load, virtually all bacteria have a rigid, highly cross-linked peptidoglycan cell wall (Holtje, 1998) that can bear substantial stress (Yao et al, 1999). Whether intracellular processes are affected by osmolality changes has not been fully investigated, how changes to mechanical load shape cellular structure and physiology

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