Analysis of the role of Bacillus subtilis      σ(M)  in β-lactam resistance reveals an essential role for c-di-AMP in peptidoglycan homeostasis.
The Bacillus subtilis extracytoplasmic function (ECF) σ factor σ(M)  is inducible by, and confers resistance to, several cell envelope-acting antibiotics. Here, we demonstrate that σ(M)  is responsible for intrinsic β-lactam resistance, with σ(X)  playing a secondary role. Activation of σ(M)  upregulates several cell wall biosynthetic enzymes including one, PBP1, shown here to be a target for the beta-lactam cefuroxime. However, σ(M)  still plays a major role in cefuroxime resistance even in cells lacking PBP1. To better define the role of σ(M)  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, σ(M)  is a known activator of disA encoding one of three paralogous diadenylate 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.
Department of Microbiology, Cornell University, Ithaca, NY 14853-8101, USA.
Yun
Y
Luo
John D
JD
Helmann
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D001412:Bacillus subtilis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002444:Cefuroxime / Q000494:pharmacology; D002473:Cell Wall / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006706:Homeostasis; D016254:Mutagenesis, Insertional; D010457:Peptidoglycan / Q000378:metabolism*; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D018440:beta-Lactam Resistance / Q000235:genetics*
D001426:Bacterial Proteins; D010457:Peptidoglycan; D012808:Sigma Factor; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D002444:Cefuroxime