Biotechnology of Horticultural Crops, Technische Universität München, Liesel-Beckmann-Straße 1, 85354 Freising, Germany.
Plasmid. 2013 Sep;70(2):216-25. doi: 10.1016/j.plasmid.2013.04.002. Epub 2013 Apr 28.
pEP36 is a plasmid ubiquitously present in Erwinia pyrifoliae, a pathogen which causes black stem blight of Asian pear. pEP36 is highly stable in its host, even in the absence of selective pressure. The plasmid is closely related to pEA29, which is widespread in E. amylovora, the causative agent of fire blight of apple and pear trees. Here we report that pEP36 possesses a functional hybrid toxin-antitoxin module, stbD/E(pEP36), with the toxin showing homology to the RelE/ParE proteins and the antidote belonging to the Phd/YefM antitoxin family. Bacteria expressing the StbE(pEP36) toxin arrest cell growth and enter a viable but non-culturable stage. However, they maintain their typical cell length and do not show filamentation. Pulse-chase experiments revealed that StbE(pEP36) acts as a global inhibitor of protein synthesis while it does not interfere with DNA and RNA synthesis. The StbD(pEP36) antitoxin is capable of neutralising StbE(pEP36) toxicity. Additional experiments show that the stbD/E(pEP36) module can stabilise plasmids at least 20-fold. Thus the toxin-antitoxin system may contribute to the remarkable stability of pEP36.
pEP36 是一种普遍存在于梨火疫病菌（Erwinia pyrifoliae）中的质粒，该病菌会导致亚洲梨树的黑茎腐烂病。pEP36 在其宿主中非常稳定，即使没有选择压力也是如此。该质粒与 pEA29 密切相关，pEA29 广泛存在于苹果火疫病的病原体——梨火疫病菌（E. amylovora）中。在这里，我们报告称 pEP36 拥有一个功能性的混合毒素-抗毒素模块 stbD/E(pEP36)，其毒素与 RelE/ParE 蛋白具有同源性，而解毒剂属于 Phd/YefM 抗毒素家族。表达 StbE(pEP36)毒素的细菌会停止细胞生长并进入存活但非可培养状态。然而，它们保持着典型的细胞长度，不会发生丝状化。脉冲追踪实验表明，StbE(pEP36) 作为一种全局蛋白质合成抑制剂发挥作用，而不会干扰 DNA 和 RNA 的合成。StbD(pEP36) 抗毒素能够中和 StbE(pEP36) 的毒性。进一步的实验表明，stbD/E(pEP36) 模块至少可以将质粒的稳定性提高 20 倍。因此，该毒素-抗毒素系统可能有助于 pEP36 的显著稳定性。
