Abstract
Bacterial cells are surrounded by an exoskeleton-like structure, the cell wall, composed primarily of the peptidoglycan (PG) sacculus. This structure is made up of glycan strands cross-linked by short peptides generating a covalent mesh that shapes bacteria and prevents their lysis due to their high internal osmotic pressure. Even though the PG is virtually universal in bacteria, there is a notable degree of diversity in its chemical structure. Modifications in both the sugars and peptides are known to be instrumental for bacteria to cope with diverse environmental challenges. In this review, we summarize and discuss the cell wall strategies to withstand biotic and abiotic environmental insults such as the effect of antibiotics targeting cell wall enzymes, predatory PG hydrolytic proteins, and PG signaling systems. Finally we will discuss the opportunities that species-specific PG variability might open to develop antimicrobial therapies.
Highlights
The presence of peptidoglycan (PG) as a key component of the bacterial cell wall is one of the defining characteristics of bacteria
O-acetylation of N-acetyl glucosamine (NAG) plays no role in lysozyme resistance, it inhibits the activity of N-acetyl-glucosaminidase Acm2, a major autolysin of L. plantarum (Bernard et al, 2011)
The innate immune system is able to recognize pathogen associated molecular patterns (PAMPs) that activate a response which depends on the molecular activator and the host. This response is characterized by the production of specific antibacterials and in more complex hosts, the activation of inflammation (Wolf and Underhill, 2018). One of these PAMPs is the bacterial PG, which is detected by pattern recognition receptors (PRR)
Summary
The presence of peptidoglycan (PG) as a key component of the bacterial cell wall is one of the defining characteristics of bacteria. The cell wall is subjected to numerous changes associated with both the growth cycle and environmental challenges (e.g., antibiotic treatment) (Schneider and Sahl, 2010; Cava and de Pedro, 2014) These changes could occur both in the peptide and/or in the sugar moieties (Vollmer et al, 2008). The sugar moieties are the target of diverse host secreted antimicrobials such as the lysozyme, a hydrolytic enzyme that cleaves the β-1, 4-glycosydic bond between the NAM and NAG. Modifications Preserving Cell Wall Integrity to overcome host lysozyme-mediated lysis by chemical modification of the NAG and NAM sugars, thereby helping bacteria to evade the host immune system. We summarize PG modifications (Figure 1 and Table 1) that confer protection to diverse antimicrobials, hydrolases and to the innate immune system
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