Analysis of the role ofBacillus subtilisσ^Min β‐lactam resistance reveals an essential role for c‐di‐AMP in peptidoglycan homeostasis

Abstract

Summary The Bacillus subtilis extracytoplasmic function (ECF) σ factor σM is inducible by, and confers resistance to, several cell envelope acting antibiotics. Here, we demonstrate that σM is responsible for intrinsic β-lactam resistance, with σX playing a secondary role. Activation of σM upregulates several cell wall biosynthetic enzymes including one, PBP1, shown here to be a target for the beta-lactam cefuroxime. However, σM still plays a major role in cefuroxime resistance even in cells lacking PBP1. To better define the role of σM in β-lactam resistance we characterized suppressor mutations that restore cefuroxime resistance to a sigM null mutant. The most frequent suppressors inactivated gdpP (yybT) which encodes a cyclic-di-AMP phosphodiesterase (PDE). Intriguingly, σM is a known activator of disA encoding one of three paralogous c-di-AMP cyclases (DAC). Overproduction of the GdpP PDE greatly sensitized cells to β-lactam antibiotics. Conversely, genetic studies indicate that at least one DAC is required for growth with depletion leading to cell lysis. These findings support a model in which c-di-AMP is an essential signal molecule required for cell wall homeostasis. Other suppressors highlight the roles of ECF σ factors in counteracting the deleterious effects of autolysins and reactive oxygen species in β-lactam treated cells.

Hydrolysis of peptidoglycan is modulated by amidation of meso‐diaminopimelic acid and Mg2+ in Bacillus subtilis

“…Furthermore, PG hydrolysis has been implicated in the mechanism of action of many antibiotics that target the cell wall (Rogers et al ., 1983; Tomasz et al ., 1970; Goodell et al ., 1976; Luo and Helmann, 2012). …”

Genome-wide screen for genes involved in eDNA release during biofilm formation by Staphylococcus aureus

“…High levels of cyclic-di-AMP have been linked to increased transcript levels of pbp4, a penicillin binding protein, which could explain the increase in peptidoglycan crosslinking (39). In B. subtilis, cyclic-di-AMP plays a role in peptidoglycan homeostasis and its depletion promotes cell lysis (40), suggesting that regulation of wall integrity may be a broadly conserved role for cyclic-di-AMP. Together with the findings of our investigation, this prior work suggests a model in which cyclic-di-AMP levels drop under biofilm-inducing conditions, impairing cell wall integrity and triggering cell lysis.…”

Cyclic Di-AMP Homeostasis in Bacillus subtilis

“…Finally, the c-di-AMP-specific phosphodiesterase GdpP (previously referred to as YybT (15)) degrades cyclic di-AMP (16). Recently, c-di-AMP was implicated in the control of cell wall homeostasis in B. subtilis, and it was demonstrated that this signaling nucleotide is essential for the growth of the bacterium (15).…”