The Bacillus subtilis Extracytoplasmic Function σ Factor σ V Is Induced by Lysozyme and Provides Resistance to Lysozyme

Abstract

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.