Analysis of the influence of peptidoglycan turnover and recycling on host-pathogen interaction in the Gram-positive pathogenStaphylococcus aureus(Peptidoglycan recycling and Gram-positive bacteria-host interaction)
Authors: Dorling Jack , Atilano Magda , Pires Elisabete , Johnson Errin , Pielach Anna , McCullagh James , Filipe Sérgio , Ligoxygakis Petros 
Published: July 2023

During peptidoglycan recycling (PR) bacteria can recover extracellular fragments of peptidoglycan (PGN) liberated by peptidoglycan turnover (PT) during cell growth and division, and reuse them in cell wall biosynthesis or central carbon metabolism. In Gram-negative bacteria, PR has been well studied, and functions in the induction of resistance to certain classes of antibiotics, and in host-pathogen interaction. However, while Gram-negative cell envelope architecture allows for highly efficient PR, Gram-positive bacteria, which lack an outer cell membrane and are instead enclosed by a glycopolymer layer, can shed large quantities of PGN-derived material to the external environment during growth. Nonetheless, the occurrence of PR was recently demonstrated in several Gram-positive bacteria, including the Gram-positive bacterial pathogenStaphylococcus aureus, and its potential adaptive functions are largely unexplored. Given the known roles of PR in Gram-negative bacteria, and that Gram-positive bacteria include several important human pathogens, we asked what role PR may play during Gram-positive pathogen-host interaction. Usingthe model insect hostDrosophila melanogaster,we demonstrate thatS. aureusmutants impaired in extracellular PGN hydrolysis (Δatl) and PGN fragment uptake (ΔmurP) show differential virulence compared to their wild-type counterpart. This was linked to increased activation of theD. melanogasterToll-cascade by spent supernatant from the Δatlmutant. Thus, we propose thatS. aureus, and potentially other Gram-positive bacteria, may use extracellular PGN degradation during PT to simultaneously process PGN fragments for recycling and for immune evasion, while recovery and/or metabolism of peptidoglycan fragments during PR may play more subtle roles in determining virulence.

Author summary

PGN is a key component of the bacterial cell wall, forming a stress-bearing sacculus surrounding the cell and providing cell shape. During growth and division, the sacculus is dynamically degraded and remodelled to ensure daughter cell separation, resulting in PT. PGN fragments released during PT can be recovered and reutilised by the cell during PR. In Gram-negative pathogens, PR is linked to antibiotic resistance, virulence and modulation of host immune recognition. In Gram-positive bacteria, PR was only recently observed. Here, we explore the roles of PT and PR in host-pathogen interaction inS. aureus, aGram-positive pathogen of significant clinical relevance. Disruption of PT inS. aureusaffected host-pathogen interaction through altering host recognition of shed PGN fragments and PR through modulation of PGN fragment recovery. This improves our understanding of the biology of this important pathogen and may aid development of novel therapeutic approaches to treatS. aureusinfections.