Archives des The Structure of Bacterial Cell Wall

Introduction

Bacteria convey unique biological structures that partly relate to a well-developped cell-wall structure structure. Thanks to the relative simplicty of

Figure 1: Schematic representation of the bacterial cell (taken from Tortora et al., 2012)

Main Features of the Bacterial Cell Wall

Bacteria are unicellular organisms, which are spread in a wide variety of environments, from our gut Modi et al., 2014 to the

Figure 2: Schematic organization and main components of the bacterial cell-envelope of (A) Gram-positive and (B) Gram-negative bacteria. Details on the typical thicknesses of the cell envelope and constituting layers of different bacterial species can be found in Vollmer & Seligman, 2010. Adapted from Silhavy et al., 2010.

The Bacterial Cell Wall

In 1884, the Danish bacteriologist, Hans Christian Gram, while trying to set up a protocol to stain bacteria for observation

Figure 5: Elasticity of the sacculus. When isolated, sacculi adopt a relaxed conformation (left) while in vivo, due to the turgor of the cell, the peptidoglycan layer is stretched (middle). Stronger forces applied to the cell wall can lead to further extension (right). Taken from Vollmer & Seligman, 2010.

Macroscopic Structure of the Peptidoglycan Layer

Although the presence of a peptidoglycan network in bacterial cell walls is well documented, the mechanical properties and architecture of

Figure 8: Chemical composition of E. coli peptidoglycan. The disaccharide-pentapeptide peptidoglycan motif is shown on the upper left, with GlcNAc in black, MurNAc in black and blue to emphasize the D-lactoyl moiety, and the peptide stem in red. The terminal 1,6-anhydroMurNac is depicted in the upper right portion of the structure. The disaccharide-pentapeptide motifs from another glycan strand are shown in green. One of the peptide stem of this additional strand is cross-linked to the m-A2pm side-chain amino group of the peptide stem of the former glycan strand through the carbonyl of its D-Ala in position 4. Atoms implicated in the peptide bond of the cross-link are shown in bold.

Peptidoglycan Molecular Structure

Chemical composition In all bacteria, the glycan strands of peptidoglycan are composed of alternating β-1,4-linked N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid

References

The Authors

Nicolas Jean Nicolas Jean obtained a Bachelor Degree in Biology and a Master Degree in Structural Biology and Biochemistry from