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.
Highlights
Reviewed by: Natividad Ruiz, The Ohio State University, United States Matthew Cabeen, Oklahoma State University, United States Ashu Sharma, University at Buffalo, United States
We explore the current knowledge of cell wall defects sensing by stress response systems, mainly in the model bacterium Escherichia coli
E. coli and other Gram-negative bacteria are equipped with sophisticated systems to monitor and convert a stress stimulus into remodeling their gene expression pattern, thereby rewiring the cell physiology to match the new environmental state
Summary
Reviewed by: Natividad Ruiz, The Ohio State University, United States Matthew Cabeen, Oklahoma State University, United States Ashu Sharma, University at Buffalo, United States. Monofunctional glycosyltransferases of the shape, elongation, division and sporulation (SEDS) family polymerize GlcNac-MurNac disaccharides from lipid II subunits into long glycan strands. These strands are crosslinked together mostly between the fourth (D-ala) and the third (diaminopimelic acid, DAP) amino acid of their peptide side chains, resulting in 4–3 D,D crosslinks whose formation is catalyzed by PenicillinBinding Proteins (PBPs). In addition to the 4–3 D,D crosslinks, non-canonical 3–3 L,D crosslinks between two DAP residues of peptide side chains are synthesized by L,Dtranspeptidases that are mostly active during stationary phase (Pisabarro et al, 1985; Magnet et al, 2007, 2008) These 3–3 crosslinks are required when defects in the LPS transport pathway occur, to strengthen the PG and avoid lysis (Morè et al, 2019). A striking example is the requirement of PBP1a for maximal fitness in alkaline conditions and of PBP1b under acidic conditions (Mueller et al, 2019), consistent with the idea that PG synthesis machinery and the general structure of the PG itself change with the environmental conditions to optimize fitness (Pazos et al, 2017)
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