毒素-抗毒素系统首先发现于低拷贝质粒，是细菌和古细菌内丰富的小型遗传元件，由染色体或质粒编码。近年发现，毒素-抗毒素系统参与细胞内多个关键的生物学过程，包括复制、转录、翻译、细胞骨架形成、细胞膜的完整性及细胞壁的形成等，但其生理功能仍需完善。希瓦氏MR-1为环境微生物的模式菌，含有稳定的内源性质粒pMR-1。pMR-1编码多对潜在毒素-抗毒素系统，但缺乏功能研究。在前期工作基础上，本项目以鉴定的两对pMR-1编码的毒素-抗毒素系统为研究对象，运用传统微生物学和现代分子遗传学手段，研究毒素的毒性机理及抗毒素的拮抗机理；探讨环境胁迫条件下毒素-抗毒素系统的响应机制；并初步揭示pMR-1编码的毒素-抗毒素系统对生物被膜形成的调控作用。本项目不仅有助于进一步解析质粒编码的毒素-抗毒素系统功能，也有助于了解质粒及其编码的毒素-抗毒素在细菌环境适应过程中的作用，并有助于挖掘二者潜在的工业应用价值。

Toxin-antitoxin systems (TAs) are prevalent in bacteria and archaea, and they are are small genetic elements encoded in prokaryotic chromosomal and plasmid DNA. The primary function of a plasmid TA module is to stabilize plasmid by eliminating plasmid-free daughter cells through a post segregation killing mechanism. In recent years, TAs were proved to act on crucial cellular processes including translation, replication, cytoskeleton formation, membrane integrity, and cell wall biosynthesis, their physiological roles remain enigmatic. Bacterial strain Shewanella oneidensis is a target of extensive research in the fields of bioelectrochemical systems and bioremediation. An endogenous plasmid pMR-1 was identified with several potential TAs presences, but studies on identification and functional characterization of TAs are largely lack in this strain. Based on previous progress, this project will focus on the functional studies of two pairs of TAs in the pMR-1 plasmid. The aim of this project is to identify and characterization of two pairs of TAs encoded by endogenous plasmid, and to study the toxic effect of toxin as well as the antitoxic activity of the antitoxin. In addition, specific efforts will be made to study the expression and regulation of the TA loci under various stresses (oxidative stress, pH stress antibiotics stress or heavy metal stress) and during biofilm formation. The proposed study will help us gain knowledge about the functions of plasmid-encoded TAs, and aid us to understand the physiological relevance of harboring endogenous plasmid especially under stress conditions. Potential industrial application of plasmid-encoded TAs to replace the use of antibiotics will also be explored in this study.