Parish T, Liu J, Nikaido H, Stoker N G
Department of Molecular and Cell Biology, University of California at Berkeley, 94720-3206, USA.
J Bacteriol. 1997 Dec;179(24):7827-33. doi: 10.1128/jb.179.24.7827-7833.1997.
A bacteriophage infection mutant (strain LIMP7) of Mycobacterium smegmatis was isolated following transposon mutagenesis. The mutant showed an unusual phenotype, in that all phages tested produced larger plaques on this strain compared to the parent strain. Other phenotypic characteristics of the mutant were slower growth, increased clumping in liquid culture, increased resistance to chloramphenicol and erythromycin, and increased sensitivity to isoniazid and several beta-lactam antibiotics. Permeability studies showed decreases in the accumulation of lipophilic molecules (norfloxacin and chenodeoxycholate) and a small increase with hydrophilic molecules (cephaloridine); taken together, these characteristics indicate an altered cell envelope. The DNA adjacent to the transposon in LIMP7 was cloned and was shown to be highly similar to genes encoding bacterial and mammalian inositol monophosphate phosphatases. Inositol is important in mycobacteria as a component of the major thiol mycothiol and also in the cell wall, with phosphatidylinositol anchoring lipoarabinomannan (LAM) in the cell envelope. In LIMP7, levels of phosphatidylinositol dimannoside, the precursor of LAM, were less than half of those in the wild-type strain, confirming that the mutation had affected the synthesis of inositol-containing molecules. The impA gene is located within the histidine biosynthesis operon in both M. smegmatis and Mycobacterium tuberculosis, lying between the hisA and hisF genes.
通过转座子诱变，分离出耻垢分枝杆菌的一种噬菌体感染突变体（菌株LIMP7）。该突变体表现出异常表型，即与亲本菌株相比，所有测试的噬菌体在该菌株上产生的噬菌斑更大。该突变体的其他表型特征包括生长较慢、液体培养中聚集增加、对氯霉素和红霉素的抗性增加，以及对异烟肼和几种β-内酰胺抗生素的敏感性增加。通透性研究表明，亲脂性分子（诺氟沙星和鹅去氧胆酸盐）的积累减少，而亲水性分子（头孢菌素）略有增加；综合这些特征表明细胞包膜发生了改变。克隆了LIMP7中转座子附近的DNA，结果显示其与编码细菌和哺乳动物肌醇单磷酸磷酸酶的基因高度相似。肌醇在分枝杆菌中很重要，它是主要硫醇分枝硫醇的组成成分，也是细胞壁的组成成分，磷脂酰肌醇将脂阿拉伯甘露聚糖（LAM）锚定在细胞包膜中。在LIMP7中，LAM的前体磷脂酰肌醇二甘露糖苷的水平不到野生型菌株的一半，这证实该突变影响了含肌醇分子的合成。impA基因位于耻垢分枝杆菌和结核分枝杆菌的组氨酸生物合成操纵子内，位于hisA和hisF基因之间。
