Department of Pathogenic Biology and Immunology, Laboratory of Infection and Immunity/School of Stomatology, Xuzhou Medical College, Xuzhou, Jiangsu 221004, China; Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
Department of Medical Microbiology and Parasitology, Institutes of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
Int J Food Microbiol. 2015 Aug 17;207:16-22. doi: 10.1016/j.ijfoodmicro.2015.04.028. Epub 2015 Apr 24.
Toxin-antitoxin (TA) systems are distributed within the genomes of almost all free-living bacteria. Although the roles of chromosomally encoded TA systems are still under debate, they are suspected to be involved in various stress responses. Here, we provide the first report of a type II TA system in the probiotic bacterium Bifidobacterium longum. Bioinformatic analysis of the B. longum JDM301 genome identified a pair of linked genes encoding a MazEF-like TA system at the locus BLJ_811-BLJ_812. Our results showed that B. longum mazEF(Bif) genes form a bicistronic operon. The over-expression of MazF(Bif) was toxic to Escherichia coli and could be neutralized by the co-expression of its cognate antitoxin MazE(Bif). We demonstrated that MazEF(Bif) was activated during acid stress, which would most likely be encountered in the gastrointestinal tract. In addition, we found that the protease ClpPX(Bif), in addition to MazEF(Bif), was induced under acid stress. Furthermore, we examined antitoxin levels over time for MazEF(Bif) and observed that the antitoxin MazE(Bif) was degraded by ClpPX(Bif), which suggested that MazEF(Bif) was activated through the hydrolysis of MazE(Bif) by ClpP1X(Bif) and ClpP2X(Bif) under acid stress. Our results suggest that the MazEF(Bif) TA module may play an important role in cell physiology and may represent a cell growth modulator that helps bacteria to cope with acid stress in the gastrointestinal tract and environment.
毒素-抗毒素 (TA) 系统广泛分布于几乎所有自由生活细菌的基因组中。虽然染色体编码的 TA 系统的作用仍存在争议，但它们被怀疑参与了各种应激反应。在这里，我们首次报道了益生菌双歧杆菌中存在的一种 II 型 TA 系统。通过对双歧杆菌 JDM301 基因组的生物信息学分析，在 BLJ_811-BLJ_812 基因座上鉴定出一对编码 MazEF 样 TA 系统的连锁基因。我们的结果表明，双歧杆菌 mazEF（Bif）基因形成一个双顺反子操纵子。MazF（Bif）的过表达对大肠杆菌有毒，并且可以被其同源抗毒素 MazE（Bif）的共表达中和。我们证明了 MazEF（Bif）在酸应激时被激活，这在胃肠道中很可能会遇到。此外，我们发现蛋白酶 ClpPX（Bif）除了 MazEF（Bif）之外，在酸应激下也被诱导。此外，我们还研究了 MazEF（Bif）的抗毒素水平随时间的变化，观察到抗毒素 MazE（Bif）被 ClpPX（Bif）降解，这表明 MazEF（Bif）在酸应激下通过 ClpP1X（Bif）和 ClpP2X（Bif）水解 MazE（Bif）而被激活。我们的结果表明，MazEF（Bif）TA 模块可能在细胞生理学中发挥重要作用，并且可能代表一种细胞生长调节剂，有助于细菌应对胃肠道和环境中的酸应激。
