Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA.
FEMS Microbiol Lett. 2018 Mar 1;365(6). doi: 10.1093/femsle/fny025.
The unique cell envelope structure of Mycobacterium tuberculosis is fundamental to its pathogenesis. Phosphatidylinositol (PI)-anchored glycolipids, such as phosphatidylinositol mannosides (PIMs), lipomannan and lipoarabinomannan, are essential components of the cell envelope widely conserved among mycobacteria, but their roles in the cell envelope integrity are not fully understood. We previously identified PimE in Mycobacterium smegmatis, a nonpathogenic model organism, as a mannosyltransferase that catalyzes the fifth mannose transfer for the biosynthesis of hexamannosyl PIMs. Our analyses, reported here, further demonstrate that the growth of the pimE deletion mutant (ΔpimE) is defective in the presence of copper. We first found that the small colony phenotype of ΔpimE on a solid Middlebrook 7H10 agar surface was alleviated when grown on M63 agar. Comparative analysis of the two media led us to identify copper in Middlebrook 7H10 as the cause of growth retardation seen in ΔpimE. We further demonstrated that ΔpimE is sensitized to several antibiotics, but the increased sensitivities were independent of the presence of copper. We conclude that the deletion of the pimE gene does not cause growth defects under optimal growth conditions, but makes the cell envelope vulnerable to toxic compounds such as copper and antibiotics.
结核分枝杆菌独特的细胞包膜结构是其发病机制的基础。磷酯酰肌醇（PI）锚定的糖脂，如磷酯酰肌醇甘露糖（PIMs）、脂阿拉伯甘露聚糖和脂阿拉伯糖脂，是广泛存在于分枝杆菌中的细胞包膜的重要组成部分，但它们在细胞包膜完整性中的作用尚未完全阐明。我们之前在非致病性模式生物耻垢分枝杆菌中鉴定出 PimE 是一种甘露糖基转移酶，它催化第五个甘露糖的转移，用于合成六甘露糖 PIMs。我们在这里报告的分析进一步表明，pimE 缺失突变体（ΔpimE）在铜存在下的生长是有缺陷的。我们首先发现，当在 M63 琼脂上生长时，ΔpimE 在固体 Middlebrook 7H10 琼脂表面的小菌落表型得到缓解。对这两种培养基的比较分析使我们确定 Middlebrook 7H10 中的铜是 ΔpimE 生长迟缓的原因。我们进一步证明，ΔpimE 对几种抗生素敏感，但增加的敏感性与铜的存在无关。我们得出结论，pimE 基因的缺失在最佳生长条件下不会导致生长缺陷，但会使细胞包膜容易受到铜和抗生素等有毒化合物的影响。
