The outer membrane is an essential load-bearing element in Gram-negative bacteria

Abstract

Gram-negative bacteria possess a complex cell envelope that consists of a plasma membrane, a peptidoglycan cell wall and an outer membrane. The envelope is a selective chemical barrier that defines cell shape and allows the cell to sustain large mechanical loads such as turgor pressure. It is widely believed that the covalently cross-linked cell wall underpins the mechanical properties of the envelope. Here we show that the stiffness and strength of Escherichia coli cells are largely due to the outer membrane. Compromising the outer membrane, either chemically or genetically, greatly increased deformation of the cell envelope in response to stretching, bending and indentation forces, and induced increased levels of cell lysis upon mechanical perturbation and during L-form proliferation. Both lipopolysaccharides and proteins contributed to the stiffness of the outer membrane. These findings overturn the prevailing dogma that the cell wall is the dominant mechanical element within Gram-negative bacteria, instead demonstrating that the outer membrane can be stiffer than the cell wall, and that mechanical loads are often balanced between these structures.

Lytic transglycosylases RlpA and MltC assist in Vibrio cholerae daughter cell separation

“…Given that daughter cell separation‐defective chains are sensitive to osmotic stress, we also hypothesized that the outer membrane (OM) may be compromised in the ∆2 LTG mutant, as the OM is an important structural and load‐bearing component of Gram‐negative bacteria (Rojas et al , ). Lysozyme typically cannot permeate the OM in sufficient quantities to cause damage to the Gram‐negative cell wall.…”

“…All experiments are representatives of at least two biological replicates. and load-bearing component of Gram-negative bacteria (Rojas et al, 2018). Lysozyme typically cannot permeate the OM in sufficient quantities to cause damage to the Gram-negative cell wall.…”

Systematic Mapping of cell Wall Mechanics in the Regulation of Cell Morphogenesis

“…Measuring the mechanical properties of the cell wall is a long-term endeavor in plant and microbial sciences. Methods to measure wall stiffness include Atomic Force Microscopy (AFM) (13), active cell bending or compression (7,8,14), and strain-stress assays through the modulation of turgor pressure (10,11,(15)(16)(17)(18). Those allow to extract a surface elasticity but are in general low-throughput, and importantly do not take into account putative global or local variations in wall thickness, thereby preventing to discern contributions from bulk material properties vs thickness to cell wall elasticity.…”

Constructing and deconstructing the bacterial cell wall

“…The prescience of his statement is evident by scores of ensuing publications. Intimate structural synergy is now recognized between the peptidoglycan and the teichoic acids of the Gram‐positive bacteria, and between the peptidoglycan and the outer membrane of the Gram‐negative bacteria . Indeed, new opportunities for antibiotic discovery have been identified that interfere with teichoic acid integration into the cell wall of Gram‐positive bacteria and with respect to lipopolysaccharide transport in Gram‐negative bacteria .…”

“…Intimate structural synergy is now recognized between the peptidoglycan and the teichoic acids of the Gram-positive bacteria, 76 and between the peptidoglycan and the outer membrane of the Gramnegative bacteria. 77,78 Indeed, new opportunities for antibiotic discovery have been identified that interfere with teichoic acid integration into the cell wall of Gram-positive bacteria 69,[79][80][81][82][83][84] and with respect to lipopolysaccharide transport in Gram-negative bacteria. [85][86][87][88][89][90] Within this universe of opportunity, we exemplify our own efforts toward the mechanistic and structural understanding of key enzymes of the bacteria with roles in cell envelope biosynthesis and antibiotic resistance.…”