New Insights into the WalK/WalR (YycG/YycF) Essential Signal Transduction Pathway Reveal a Major Role in Controlling Cell Wall Metabolism and Biofilm Formation inStaphylococcus aureus

Abstract

The highly conserved WalK/WalR (also known as YycG/YycF) two-component system is specific to low-G؉C gram-positive bacteria. While this system is essential for cell viability, both the nature of its regulon and its physiological role have remained mostly uncharacterized. We observed that, unexpectedly, Staphylococcus aureus cell death induced by WalKR depletion was not followed by lysis. We show that WalKR positively controls autolytic activity, in particular that of the two major S. aureus autolysins, AtlA and LytM. By using our previously characterized consensus WalR binding site and carefully reexamining the genome annotations, we identified nine genes potentially belonging to the WalKR regulon that appeared to be involved in S. aureus cell wall degradation. Expression of all of these genes was positively controlled by WalKR levels in the cell, leading to high resistance to Triton X-100-induced lysis when the cells were starved for WalKR. Cells lacking WalKR were also more resistant to lysostaphin-induced lysis, suggesting modifications in cell wall structure. Indeed, lowered levels of WalKR led to a significant decrease in peptidoglycan biosynthesis and turnover and to cell wall modifications, which included increased peptidoglycan cross-linking and glycan chain length. We also demonstrated a direct relationship between WalKR levels and the ability to form biofilms. This is the first example in S. aureus of a regulatory system positively controlling autolysin synthesis and biofilm formation. Taken together, our results now define this signal transduction pathway as a master regulatory system for cell wall metabolism, which we have accordingly renamed WalK/WalR to reflect its true function.

Pathogen-mediated manipulation of arthropod microbiota to promote infection

“…Similarities in the relative abundance of Enterococci within the tick gut, found by microbiome analysis or SEM imaging of tick gut biofilms when treated with D-serine, to those during A. phagocytophilum infection or P1 injection of tick guts support the mechanistic action of IAFGP's peptidoglycan binding activity on modulating the tick microbiota. D-amino acids interfere with the linking of biofilm adhesion proteins, and with cell wall remodeling (51)(52)(53)(54). Therefore, we hypothesized that IAFGP binding to peptidoglycan could cause alterations in bacterial physiology and morphology that would reduce the ability of Gram-positive bacteria to form tenacious biofilms-adversely affecting the relative composition of the gut microbiota.…”

Molecular Bases Determining Daptomycin Resistance-Mediated Resensitization to β-Lactams (Seesaw Effect) in Methicillin-Resistant Staphylococcus aureus

“…Decreased susceptibility to DAP in S. aureus has been reported to lead to clinical failures in patients with MRSA deep-site infections, such as endocarditis and abscesses (28)(29)(30). Previously, we identified two major factors that mutually cooperate in the acquisition of DAP resistance; one is related to the cell membrane (mrpF mutations), and the second affects cell wall factors (VraSR) (6).…”

The action mechanism of daptomycin

“…It encodes the yycFG response regulator system, which controls cell wall metabolism and biofilm formation. 108,109 in vitro -derived resistant mutants of Staphylococcus aureus exhibited changes affecting the histidine kinase of the system (YycG). 110,111 In Bacillus subtilis, this protein is located at the cell division septum, where it regulates cell division and wall restructuring.…”