Department of Microbiology, Cornell University, Ithaca, NY 14853-8101, USA.
Mol Microbiol. 2012 Feb;83(3):623-39. doi: 10.1111/j.1365-2958.2011.07953.x. Epub 2012 Jan 4.
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.
枯草芽孢杆菌细胞外功能（ECF）σ因子σ（M）可被多种细胞包膜作用的抗生素诱导，并赋予其抗性。在这里，我们证明σ（M）负责固有β-内酰胺抗性，而σ（X）起次要作用。σ（M）的激活上调了几种细胞壁生物合成酶，包括在这里显示为β-内酰胺头孢呋辛的靶标 PBP1。然而，即使在缺乏 PBP1 的细胞中，σ（M）在头孢呋辛抗性中仍发挥主要作用。为了更好地定义σ（M）在β-内酰胺抗性中的作用，我们对恢复 sigM 缺失突变体头孢呋辛抗性的抑制突变进行了表征。最常见的抑制剂失活了 gdpP（yybT），该基因编码环二腺苷酸磷酸二酯酶（PDE）。有趣的是，σ（M）是一种已知的 disA 激活因子，编码三个同源二腺苷酸环化酶（DAC）之一。GdpP PDE 的过度产生使细胞对β-内酰胺抗生素极为敏感。相反，遗传研究表明，至少有一种 DAC 是细胞生长所必需的，耗尽后会导致细胞裂解。这些发现支持 c-di-AMP 是一种必需的信号分子，用于维持细胞壁内稳态的模型。其他抑制剂突出了 ECF σ 因子在对抗β-内酰胺处理细胞中自溶素和活性氧的有害影响中的作用。
