SXT/R391整合性接合元件是近年来在细菌中发现的一种可移动的基因元件，它位于染色体上，可通过接合转移的方式介导细菌间基因的水平转移。许多SXT/R391元件包含耐药基因，这些元件的扩散加速了耐药基因在同种及不同种属之间的传播，造成细菌多重耐药问题日益严重。携带SXT/R391 的细菌在临床和环境中出现的频率逐渐增高。SXT/R391 元件的进化能造成其扩散能力的增强。目前有关SXT/R391 元件的进化的知识很匮乏。本项目在充分利用现有的SXT/R391 ICEs基因组数据的基础上，结合我们测定的SXT序列，利用泛基因组模型、系统发生地理学、溯祖分析等技术，拟从全基因组角度探讨SXT/R391元件之间的进化关系，并结合适应性进化分析，揭示SXT/R391元件在扩散传播经历的微进化特征，以还原SXT/R391基因组的动力学过程，重构这个移动遗传因子家族的起源、传播经历的进化历程的全貌。

Integrative and conjugative elements (ICEs) have recently been shown to be the most abundant conjugative elements in practically all prokaryotic clades. ICEs are self-transmissible mobile genetic elements able to confer multidrug resistance and other adaptive features to bacterial hosts. As such, ICEs are a major driving force of bacterial genome evolution allowing rapid acquisition of a variety of new traits and adaptive functions such as virulence, metabolic pathways and resistance to antimicrobial compounds, heavy metals or bacteriophage infection. To date, various types of ICEs have been identified in both Gram negative and Gram positive bacteria. The SXT/R391 family is one of the largest, diverse and well-studied set of ICEs among Gram-negative bacteria. ICEs of the SXT/R391 family have been recognized as key drivers of antibiotic resistance dissemination in the seventh-pandemic lineage of Vibrio cholerae. SXT/R391 ICEs propagate by conjugation and integrate site-specifically into the chromosome of a wide range of environmental and clinical bacteria..In recent years, SXT/R391 ICEs have been the subject of extensive study and while there is growing understanding of their prevalence, diversity, and molecular aspects. However, our understanding of ICE evolution is only beginning to be unraveled. The knowledge of evolutionary origin, migration patterns, and corresponding demography history of SXT/R391 ICEs is poor. Increasing such knowledge would help us better prevent and control the spreading of SXT/R391 element. .In this study, aiming to access the spreading mechanism and evolution of SXT/R391 ICEs in global source, many bioinformatic studies will be performed with all SXT/R391 ICE genome sequences available, including sequences retrieved from publicly sequence databases and intact SXT sequences from the genome sequenced V. cholerae strains in this project. First, comparative ICE genomic and pan-genomic analysis will be performed to explore the evolutionary relationship. Second, Bayesian phylogeography framework would be applied to determine the source, migration patterns, and corresponding demography history of the SXT/R391 ICEs that circulated in all bacteria. Third, the relationship between the host range of an ICE and the genetic content of the permissive (or nonpermissive) hosts will be well understood. Finally, the temporal dynamics of SXT-R391 ICE origin and spread will be reconstructed and all evolutionary events generating significant diversity in ICEs will be identified..These results will be helpful for better understanding of the evolution profile and spreading mechanism of bacterial SXT/R391 ICEs. This study will provide useful information for prevention and control of the transferring of SXT/R391 element.