How Bacteria Consume Their Own Exoskeletons (Turnover and Recycling of Cell Wall Peptidoglycan)

Abstract

SUMMARY The phenomenon of peptidoglycan recycling is reviewed. Gram-negative bacteria such as Escherichia coli break down and reuse over 60% of the peptidoglycan of their side wall each generation. Recycling of newly made peptidoglycan during septum synthesis occurs at an even faster rate. Nine enzymes, one permease, and one periplasmic binding protein in E. coli that appear to have as their sole function the recovery of degradation products from peptidoglycan, thereby making them available for the cell to resynthesize more peptidoglycan or to use as an energy source, have been identified. It is shown that all of the amino acids and amino sugars of peptidoglycan are recycled. The discovery and properties of the individual proteins and the pathways involved are presented. In addition, the possible role of various peptidoglycan degradation products in the induction of β-lactamase is discussed.

Trehalose-recycling ABC transporter LpqY-SugA-SugB-SugC is essential for virulence of Mycobacterium tuberculosis

“…The observed dispensability of trehalose recycling for Mtb persistence in mice during the chronic infection phase is consistent with the assumption that this phase is characterized by limited replication, and hence minimal requirement for cell wall biosynthesis, of the bacilli, and hence minimal coupled secretion of trehalose. The described recycling strategy to preserve scarce resources suggests a previously unexplored context for understanding the function of many importers for sugars and other metabolites in Mtb and in other microbes occupying nutrientdeficient environments as saprophytes, pathogens or commensals, resembling recycling of cell wall peptidoglycan breakdown products by bacteria (30). However, to our knowledge, this is a unique function for an ABC sugar transporter and a previously unappreciated aspect of mycobacterial pathogenesis.…”

The β-Lactamase Gene Regulator AmpR Is a Tetramer That Recognizes and Binds the d-Ala-d-Ala Motif of Its Repressor UDP-N-acetylmuramic Acid (MurNAc)-pentapeptide

“…In the absence of ␤-lactams, UDP-MurNAc-pentapeptide binds to AmpR and causes the repression of ampC transcription (16). In contrast, disruption of PG metabolism by ␤-lactams increases the cytosolic concentration of 1,6-anhydroMurNAc-peptides, which appears to overwhelm endogenous AmpD activity and allows either the 1,6-anhydroMurNAc-tripeptide (16,17) or -pentapeptide species (7,18) to bind to AmpR. It has been proposed that these 1,6-anhydroMurNAc species competitively displace UDP-MurNAc-pentapeptide from AmpR, thus converting AmpR into an activator of ampC transcription (16,19).…”

“…1) (5,6). Despite its critical structural role, PG is a dynamic macromolecule that is continuously turned over and recycled during microbial growth (5)(6)(7)(8). Turnover is carried out by periplasmic autolysins that excise GlcNAc-␤(134)-1,6-anhydroMurNAc-peptide fragments from the PG sacculus (9), and the fragments are transported to the cytosol by the AmpG permease (10) for recycling.…”

Mycobacterium tuberculosis FtsX extracellular domain activates the peptidoglycan hydrolase, RipC

“…Inside the cell, the bacterial chromosome is replicated, and ATP-driven machines disentangle the products and segregate the genetic material (1). Outside the cell, the peptidoglycan (PG)-the main component of the bacterial cell wall-is synthesized in a spatially defined pattern that forms a continuous sacculus that is hydrolyzed at precisely the right time and place to allow the daughter cells to separate (2)(3)(4). If the critical PG hydrolases are not activated, the cells form long chains that are covalently connected (5).…”