ICE介导猪链球菌mutT缺陷型突变子形成及调控细菌发生“突变-ICE水平转移”转换的机制

ICE是介导耐药基因水平转移的重要元件；“GO”修复系统MutT缺陷是细菌产生突变子的重要原因。前期研究显示ICE可在猪链球菌mutT基因内整合和切除，但二者的相互作用及其机制尚不明确。本项目基于前期积累，推测ICE可通过其在mutT的整合/切除形成调控mutT转录的开关，介导猪链球菌响应ROS突变子的产生，并影响ICE水平转移，以获取最大生存利益。为证实该科学假设，本项目拟开展下述研究：1）明确猪链球菌MutT的GO修复功能；2）解析ICE整合对mutT的转录重构及ICE切除对MutT缺陷型突变子形成的机制；3）评估ICE_mutT重构株响应各种胁迫诱导耐药性突变产生及ICE水平转移的能力；4）阐明ICE的切除/整合作为调节开关进行“突变-水平转移”转换的机制。上述内容的完成可充分阐明猪链球菌ICE在维持细菌染色体稳定性和变异性之间动态平衡的调控作用以及细菌耐药性产生过程涉及的复杂机制。

ICE is an important mobile genetic element in mediating the horizontal transmission of antimicrobial resistance (AMR) genes among gram-positive bacteria. Defect in guanine oxide repair protein MutT is one of the most important reason for mutator formation. Our pioneer study showed that ICE could integrate at the site of mutT in Streptococcus. suis (S. suis). However, our understanding on ICE-mutation interaction is still restricted to few reports and need to be unraveled. Based on our achievement in field of streptococcal ICE and the evidence from the preliminary data, we generate the hypothesis that an ICE regulatory switch will be formed which is driven by integrating and excising from the mutT gene of the host, a member of “GO” repair system, therefore changing the transcription of mutT and modulating their mutation rates of AMR as well as horizontal transfer of ICE. Thus, in this study, we will focus on investigating the following scientific issues by using a series of molecular biological methods to clarify the involved mechanisms: 1) to identify the GO repair function of MutT in S. suis; 2) to elucidate the mechanisms of ICE integration on mutT transcription reconstruction and ICE excision on the formation of mutator; 3) to evaluate the ability of mutation generation and ICE level retransfer of the reconstructed ICE_mutT strain responding to various stress; 4) to clarify the mechanism involved in " mutation-horizontal transfer" conversion through ICE integration and excision from the site of mutT. Through the completion of the above contents, the regulatory role of S. suis ICE in maintaining the dynamic balance between chromosome stability and variability and the complex mechanism involved in the development of bacterial resistance were fully elucidated. Solving the above key scientific problems will help us to understand the regulatory role of ICE in maintaining the dynamic balance between chromosome stability and variability and the complex mechanism involved in the development of bacterial resistance of S. suis, which has a far-reaching significance of high practical relevance and theory point of the view.