Analysis of the role of Bacillus subtilis σ(M) in β-lactam resistance reveals an essential role for c-di-AMP in peptidoglycan homeostasis

Mol Microbiol. 2012 Feb;83(3):623-39. doi: 10.1111/j.1365-2958.2011.07953.x. Epub 2012 Jan 4.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • 3',5'-Cyclic-AMP Phosphodiesterases / metabolism
  • Bacillus subtilis / drug effects
  • Bacillus subtilis / genetics*
  • Bacillus subtilis / metabolism
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cefuroxime / pharmacology
  • Cell Wall / metabolism
  • Cyclic AMP / metabolism*
  • Gene Expression Regulation, Bacterial
  • Homeostasis
  • Mutagenesis, Insertional
  • Peptidoglycan / metabolism*
  • Sigma Factor / genetics
  • Sigma Factor / metabolism*
  • beta-Lactam Resistance / genetics*

Substances

  • Bacterial Proteins
  • Peptidoglycan
  • Sigma Factor
  • Cyclic AMP
  • 3',5'-Cyclic-AMP Phosphodiesterases
  • Cefuroxime