Department of Microbiology, Cornell University, Ithaca, NY 14853-8101, USA.
Mol Microbiol. 2011 Jul;81(1):69-79. doi: 10.1111/j.1365-2958.2011.07679.x. Epub 2011 Jun 9.
Bacteria respond to physical and chemical stresses that affect the integrity of the cell wall and membrane by activating an intricate cell envelope stress response. The ability of cells to regulate the biophysical properties of the membrane by adjusting fatty acid composition is known as homeoviscous adaptation. Here, we identify a homeoviscous adaptation mechanism in Bacillus subtilis regulated by the extracytoplasmic function σ factor σ(W). Cell envelope active compounds, including detergents, activate a sense-oriented, σ(W)-dependent promoter within the first gene of the fabHa fabF operon. Activation leads to a decrease in the amount of FabHa coupled with an increase in FabF, the initiation and elongation condensing enzymes of fatty acid biosynthesis respectively. Downregulation of FabHa results in an increased reliance on the FabHb paralogue leading to a greater proportion of straight chain fatty acids in the membrane, and the upregulation of FabF increases the average fatty acid chain length. The net effect is to reduce membrane fluidity. The inactivation of the σ(W)-dependent promoter within fabHa increased sensitivity to detergents and to antimicrobial compounds produced by other Bacillus spp. Thus, the σ(W) stress response provides a mechanism to conditionally decrease membrane fluidity through the opposed regulation of FabHa and FabF.
细菌通过激活复杂的细胞包膜应激反应来应对影响细胞壁和膜完整性的物理和化学应激。细胞通过调节脂肪酸组成来调节膜的生物物理性质的能力被称为同型粘适应性。在这里，我们确定了枯草芽孢杆菌中由胞外功能 σ 因子 σ(W)调节的同型粘适应机制。细胞膜活性化合物，包括清洁剂，在 fabHa fabF 操纵子的第一个基因内激活定向的、σ(W)依赖性启动子。激活导致 FabHa 的量减少，同时 FabF 增加，FabF 分别是脂肪酸生物合成的起始和延伸缩合酶。FabHa 的下调导致对 FabHb 同源物的依赖性增加，导致膜中直链脂肪酸的比例增加，FabF 的上调增加了平均脂肪酸链长。其净效应是降低膜流动性。fabHa 内的 σ(W)依赖性启动子失活增加了对清洁剂和其他芽孢杆菌产生的抗菌化合物的敏感性。因此，σ(W)应激反应提供了一种通过相反调节 FabHa 和 FabF 来有条件降低膜流动性的机制。
