title: The Bacillus subtilis extracytoplasmic function σ factor σ(V) is induced by lysozyme and provides resistance to lysozyme.
abstract: Bacteria encounter numerous environmental stresses which can delay or inhibit their growth. Many bacteria utilize alternative σ factors to regulate subsets of genes required to overcome different extracellular assaults. The largest group of these alternative σ factors are the extracytoplasmic function (ECF) σ factors. In this paper, we demonstrate that the expression of the ECF σ factor σ(V) in Bacillus subtilis is induced specifically by lysozyme but not other cell wall-damaging agents. A mutation in sigV results in increased sensitivity to lysozyme killing, suggesting that σ(V) is required for lysozyme resistance. Using reverse transcription (RT)-PCR, we show that the previously uncharacterized gene yrhL (here referred to as oatA for O-acetyltransferase) is in a four-gene operon which includes sigV and rsiV. In quantitative RT-PCR experiments, the expression of oatA is induced by lysozyme stress. Lysozyme induction of oatA is dependent upon σ(V). Overexpression of oatA in a sigV mutant restores lysozyme resistance to wild-type levels. This suggests that OatA is required for σ(V)-dependent resistance to lysozyme. We also tested the ability of lysozyme to induce the other ECF σ factors and found that only the expression of sigV is lysozyme inducible. However, we found that the other ECF σ factors contributed to lysozyme resistance. We found that sigX and sigM mutations alone had very little effect on lysozyme resistance but when combined with a sigV mutation resulted in significantly greater lysozyme sensitivity than the sigV mutation alone. This suggests that sigV, sigX, and sigM may act synergistically to control lysozyme resistance. In addition, we show that two ECF σ factor-regulated genes, dltA and pbpX, are required for lysozyme resistance. Thus, we have identified three independent mechanisms which B. subtilis utilizes to avoid killing by lysozyme.
authors.affiliation: Department of Microbiology, Carver College of Medicine, University of Iowa, 51 Newton Rd., Iowa City, IA 52242, USA.
authors.forename: Theresa D
authors.initials: TD
authors.lastname: Ho
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Hastie
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Intile
authors.forename: Craig D
authors.initials: CD
authors.lastname: Ellermeier
mesh_terms: D001412:Bacillus subtilis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D015964:Gene Expression Regulation, Bacterial; D009113:Muramidase / Q000378:metabolism* / Q000494:pharmacology; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor; D009113:Muramidase