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. Author manuscript; available in PMC: 2022 Apr 1.
Published in final edited form as: Nat Rev Microbiol. 2021 Nov 3;20(4):236–248. doi: 10.1038/s41579-021-00638-0

Figure 1: The Gram-negative outer membrane has a diverse makeup and a wide variety of physical and mechanical properties.

Figure 1:

A) The cytoplasm of all bacterial cells is surrounded by an inner membrane (IM) composed of phospholipids and inner membrane proteins (IMPs), which is enclosed by the cell wall (CW), a macromolecular network of peptidoglycan (PG) that single-layered in E. coli29. In Gram-negative bacteria, the cell wall resides in the periplasm, a ~15-nm thick aqueous compartment enclosed by the inner and outer membranes. The outer membrane (OM) is asymmetric, composed of phospholipids in the inner leaflet and lipopolysaccharides (LPS), along with outer membrane proteins (OMPs) such as porins and lipoproteins such as Lpp, which links the OM and PG.

B) The OM (red) can exhibit variable composition, spatial heterogeneity, solid- or fluid-like rheology (diffusive dynamics), and the ability to bear mechanical stresses of similar magnitude to the cell wall (green). As a result, the chemical, physical, and mechanical properties of the OM can have broad impacts on bacterial physiology.