细菌整合性接合元件SXT/R391研究进展

Bacterial SXT/R391 family from integrating conjugative elements－A review

摘要:

摘要: SXT/Ｒ391家族是整合性接合元件中多样性最为丰富、成员最多的一个家族。SXT/Ｒ391包括保守的核基因以及可变区基因，SXT/Ｒ391保守的核心基因主要涉及SXT/Ｒ391的整合/剪切、自我接合转移、元件表达的调节。SXT/Ｒ391可变区基因的编码产物主要负责宿主对抗生素的耐药性、重金属离子抗性、生物膜形成和细菌运动能力的调节，编码毒素-抗毒素系统以阻止SXT/Ｒ391从宿主丢失。一些SXT/Ｒ391也编码限制性修饰系统、解旋酶、核酸内切酶。SXT/Ｒ391 受SetCD正性调控，受SetＲ负性调控。SXT/Ｒ391接合转移过程不会导致其在原供体菌基因组丢失。SXT/Ｒ391可以阻止细胞获得其它密切相关的同类SXT/Ｒ391但不排斥异质性ICE获得，在SXT/Ｒ391自身编码的重组系统作用下获得的异质性ICE导致杂合ICE的产生。SXT/Ｒ391具有相当高的转移频率和宽广宿主范围，目前已经有超过40个不同类型的SXT/Ｒ391在不同种属的细菌中被发现，以弧菌为最多。已知的SXT/Ｒ391集中出现在非洲和亚洲沿海地区，且来源多为海洋细菌，表明海洋环境很可能是SXT/Ｒ391主要的贮藏库，并且经由海洋环境株向临床株扩散。日益增加的选择压力很可能加速了SXT/Ｒ391的传播。鉴于SXT/Ｒ391的转移和盛行带来的风险，卫生部门以及医学微生物科学家应对其扩散保持充分警惕。

Abstract:

Abstract: SXT/R391 family has the most abundant types and members in integrating conjugative elements (ICE)．SXT/R391 elements are comprised of conservative core genes and genes in variable regions．The functions of conservative core genes of SXT/R391 include integration and excision，self-transfer through conjugation，and regulation of its expression．The genes in the variable regions often encode for drug and heavy metal resistances，forming of biofilm，adjustment of bacterial motility，and toxin-antitoxin systems that prevent SXT/R391 deletion from hosts．Some genes in variable region of SXT/R391 also encode for restriction-modification system，helicase，and endonuclease．The activity of SXT/R391is positively regulated by activator SetCD，and negatively regulated by repressor SetR．SXT/R391 cannot be easily deleted from the primary donors in the process of transfer．SXT/R391 prevent the acquirement of closely related and homogeneous elements but cannot prevent the acquirement of heterogenetic ICE，which leads to the generation of hybrid ICE under the action of recombination system encoded by SXT/R391 themselves．SXT/R391 have high transferable frequency and wide host range，and until now more than 40 different SXT/R391 elements have been discovered in various bacteria，especially in Vibrio species，which mainly distribute in coastal areas in Asia and Africa．It suggests that marine environments are likely the main reservoir for SXT /Ｒ391 and these elements probably spread from marine environmental strains to clinical strains，under increasing selective pressure．Due to the hazard caused by the prevalence and the transfer of SXT/R391，medical microbiologist and health departments should be fully alert to the spread of the elements.