Department of Oral Microbiology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Department of Periodontology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Microbiologyopen. 2019 Nov;8(11):e791. doi: 10.1002/mbo3.791. Epub 2019 Jan 17.
Nisin A is a lantibiotic produced by Lactococcus lactis that is widely used as a food preservative. In Staphylococcus aureus, the BraRS two-component system (TCS) senses nisin A and regulates the expression of the ABC transporter VraDE, which is responsible for nisin A resistance. In this study, we exposed S. aureus to a sub-minimum inhibition concentration of nisin A and obtained three spontaneous mutants that were highly resistant to this lantibiotic, designated as SAN (S. aureus nisin resistant) 1, SAN8, and SAN87. In the wild-type S. aureus strain, VraDE expression was induced by nisin A. In contrast, SAN8 and SAN87 showed constitutively high VraDE expression, even in the absence of nisin A, while SAN1 showed higher BraRS expression, which resulted in high VraDE expression in the presence of nisin A. We identified a single mutation in the promoter region of braXRS in SAN1, whereas SAN8 and SAN87 had single mutations in braR and braS, respectively. Interestingly, even the unphosphorylated form of the mutant BraR protein induced VraDE expression. These results indicate that conformational changes in BraS or BraR resulting from the point mutations may result in the constitutive expression of VraDE, allowing S. aureus to adapt to high concentrations of nisin A.
乳链菌肽 A 是由乳酸乳球菌产生的一种细菌素,被广泛用作食品防腐剂。在金黄色葡萄球菌中,BraRS 双组分系统 (TCS) 可感知乳链菌肽 A,并调节 ABC 转运蛋白 vraDE 的表达,该蛋白负责乳链菌肽 A 的耐药性。在这项研究中,我们将金黄色葡萄球菌暴露于亚最小抑制浓度的乳链菌肽 A 下,获得了三种对这种细菌素高度耐药的自发突变体,分别命名为 SAN(金黄色葡萄球菌乳链菌肽耐药)1、SAN8 和 SAN87。在野生型金黄色葡萄球菌菌株中,乳链菌肽 A 诱导 vraDE 的表达。相比之下,SAN8 和 SAN87 表现出持续的高 vraDE 表达,即使没有乳链菌肽 A,而 SAN1 表现出更高的 BraRS 表达,导致在存在乳链菌肽 A 时 vraDE 表达增加。我们在 SAN1 中鉴定出 braXRS 启动子区域的单个突变,而 SAN8 和 SAN87 分别在 braR 和 braS 中具有单个突变。有趣的是,即使是突变的非磷酸化形式的 BraR 蛋白也能诱导 vraDE 的表达。这些结果表明,由于点突变导致的 BraS 或 BraR 的构象变化可能导致 vraDE 的持续表达,使金黄色葡萄球菌能够适应高浓度的乳链菌肽 A。