Université de Lorraine, LCPME, UMR7564, Villers-lès-Nancy, France; CNRS, LCPME, UMR7564, Villers-lès-Nancy, France.
FEMS Microbiol Rev. 2014 Jul;38(4):720-60. doi: 10.1111/1574-6976.12058. Epub 2014 Jan 27.
Horizontal transfer of genomic islands (GEIs), that is, chromosomal regions encoding functions that can be advantageous for the host, plays a key role in bacterial evolution, but their mechanisms of transfer remained elusive for a long time. Recent data suggest that numerous GEIs belong to noncanonical classes of mobile genetic elements (MGEs) that can transfer by conjugation. Among them, the integrative and conjugative elements encode their own excision, conjugative transfer, and integration, whereas the integrative mobilizable elements are autonomous for excision and integration but require the conjugation machinery of helper elements to transfer. Others can self-transfer but require the recombination machinery of the recipient cell to integrate. All these MGEs evolve by acquisition, deletion, or exchange of modules, that is, groups of genes involved in the same function. Moreover, composite GEIs can result from the insertion of a MGE within another or from the site-specific integration of an incoming MGE into one of the recombination sites flanking a resident GEI (tandem accretion). Tandem accretion enables the cis-conjugative mobilization of highly degenerated and nonautonomous GEIs, the cis-mobilizable elements. All these mechanisms contribute to the plasticity and complex evolution of GEIs and explain the highly diverse tableau revealed by more and more genome comparisons.
基因岛（GEIs）的水平转移，即编码对宿主有利的功能的染色体区域的转移，在细菌进化中起着关键作用，但它们的转移机制长期以来一直难以捉摸。最近的数据表明，许多 GEIs 属于非典型类别的可移动遗传元件（MGEs），可以通过接合进行转移。其中，整合和共轭元件编码其自身的切除、共轭转移和整合，而整合可移动元件则可以自主进行切除和整合，但需要辅助元件的接合机制进行转移。其他元件可以自我转移，但需要受体细胞的重组机制进行整合。所有这些 MGEs 通过获取、删除或模块交换（涉及同一功能的基因群）进化。此外，复合 GEIs 可以通过 MGE 插入另一个 MGE 内或通过外来 MGE 特异性整合到驻留 GEI 侧翼的一个重组位点（串联积累）中来产生。串联积累使高度退化和非自主的 GEIs（顺式可移动元件）的顺式共轭运动成为可能。所有这些机制都有助于 GEIs 的可塑性和复杂进化，并解释了越来越多的基因组比较所揭示的高度多样化的情况。
