A Fly on the Wall: How Stress Response Systems Can Sense and Respond to Damage to Peptidoglycan

Abstract

The envelope of Gram-negative bacteria is critical for survival across a wide range of environmental conditions. The inner membrane, the periplasm and the outer membrane form a complex compartment, home to many essential processes. Hence, constant monitoring by envelope stress response systems ensure correct biogenesis of the envelope and maintain its homeostasis. Inside the periplasm, the cell wall, made of peptidoglycan, has been under the spotlight for its critical role in bacterial growth as well as being the target of many antibiotics. While much research is centered around understanding the role of the many enzymes involved in synthesizing the cell wall, much less is known about how the cell can detect perturbations of this assembly process, and how it is regulated during stress. In this review, we explore the current knowledge of cell wall defects sensing by stress response systems, mainly in the model bacterium Escherichia coli. We also discuss how these systems can respond to cell wall perturbations to increase fitness, and what implications this has on cell wall regulation.

Keywords: BAE; Cpx; ESRS; Psp; RCS; cell wall; sigmaE; stress response.

Figure 1

Overview of cell wall synthesis in E. coli. (A). The synthesis of PG in the periplasm from lipid II precursors in the cytoplasm, with indications of the main synthetic, and lytic activities involved. Figure inspired by Typas et al. (2012), Cho S.H. et al. (2014), and Zhao et al. (2017).

Figure 2

Overview of the major envelope stress response systems of E. coli. (A). Schematics of the two-component systems of E. coli that act as ESRS, the Cpx, Bae and Rcs systems. (B) Schematics of alternative response systems that act as ESRS, the σ^E and the Psp responses. Figure inspired by Guest et al. (2017) and Mitchell and Silhavy (2019).

Figure 3

Schematics of additional response systems that deal with PG stress. (A). Schematics of the DpiBA two-component system. (B) Schematics of the WigKR two-component system of Vibrio cholerae.