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Comparative ICE Genomics: Insights into the Evolution of the SXT/R391 Family of ICEs

机译：比较ICE基因组学：SXT / R391 ICE系列进化的见解

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Integrating and conjugative elements (ICEs) are one of the three principal types of self-transmissible mobile genetic elements in bacteria. ICEs, like plasmids, transfer via conjugation; but unlike plasmids and similar to many phages, these elements integrate into and replicate along with the host chromosome. Members of the SXT/R391 family of ICEs have been isolated from several species of gram-negative bacteria, including Vibrio cholerae, the cause of cholera, where they have been important vectors for disseminating genes conferring resistance to antibiotics. Here we developed a plasmid-based system to capture and isolate SXT/R391 ICEs for sequencing. Comparative analyses of the genomes of 13 SXT/R391 ICEs derived from diverse hosts and locations revealed that they contain 52 perfectly syntenic and nearly identical core genes that serve as a scaffold capable of mobilizing an array of variable DNA. Furthermore, selection pressure to maintain ICE mobility appears to have restricted insertions of variable DNA into intergenic sites that do not interrupt core functions. The variable genes confer diverse element-specific phenotypes, such as resistance to antibiotics. Functional analysis of a set of deletion mutants revealed that less than half of the conserved core genes are required for ICE mobility; the functions of most of the dispensable core genes are unknown. Several lines of evidence suggest that there has been extensive recombination between SXT/R391 ICEs, resulting in re-assortment of their respective variable gene content. Furthermore, our analyses suggest that there may be a network of phylogenetic relationships among sequences found in all types of mobile genetic elements.
机译：整合和结合元件（ICEs）是细菌中自我传递的移动遗传元件的三种主要类型之一。 ICE，如质粒，通过结合转移。但是与质粒不同并且与许多噬菌体相似，这些元件整合到宿主染色体中并与宿主染色体一起复制。 SXT / R391 ICEs家族的成员已从数种革兰氏阴性细菌中分离出来，包括霍乱弧菌霍乱弧菌，在霍乱弧菌中，它们已成为传播赋予对抗生素抗性基因的重要载体。在这里，我们开发了一个基于质粒的系统来捕获和分离SXT / R391 ICE，以进行测序。对来自不同宿主和位置的13个SXT / R391 ICE的基因组进行的比较分析表明，它们包含52个完全同义且几乎相同的核心基因，这些基因充当能够动员可变DNA阵列的支架。此外，维持ICE流动性的选择压力似乎限制了可变DNA插入不中断核心功能的基因间位点。可变基因赋予不同的元件特异性表型，例如对抗生素的抗性。对一组缺失突变体的功能分析表明，ICE迁移所需的保守核心基因不到一半。大多数可有可无的核心基因的功能尚不清楚。几条证据表明，SXT / R391 ICE之间存在广泛的重组，导致它们各自可变基因含量的重新分配。此外，我们的分析表明，在所有类型的移动遗传元件中发现的序列之间都可能存在系统发育关系网络。

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