IHAP, Université de Toulouse, INRA, Ecole Nationale Vétérinaire de Toulouse, 23 chemin des Capelles, BP 87614, 31076 Toulouse cedex 3, France IHAP, Université de Toulouse, INRA, Ecole Nationale Vétérinaire de Toulouse, 23 chemin des Capelles, BP 87614, 31076 Toulouse cedex 3, France IHAP, Université de Toulouse, INRA, Ecole Nationale Vétérinaire de Toulouse, 23 chemin des Capelles, BP 87614, 31076 Toulouse cedex 3, France Institute of Plant and Microbial Biology, Academia Sinica, Taiwan IHAP, Université de Toulouse, INRA, Ecole Nationale Vétérinaire de Toulouse, 23 chemin des Capelles, BP 87614, 31076 Toulouse cedex 3, France.
Curr Issues Mol Biol. 2018;29:3-22. doi: 10.21775/cimb.029.003. Epub 2018 Apr 12.
The class Mollicutes (trivial name "mycoplasma") is composed of wall-less bacteria with reduced genomes whose evolution was long thought to be only driven by gene losses. Recent evidences of massive horizontal gene transfer (HGT) within and across species provided a new frame to understand the successful adaptation of these minimal bacteria to a broad range of hosts. Mobile genetic elements are being identified in a growing number of mycoplasma species, but integrative and conjugative elements (ICEs) are emerging as pivotal in HGT. While sharing common traits with other bacterial ICEs, such as their chromosomal integration and the use of a type IV secretion system to mediate horizontal dissemination, mycoplasma ICEs (MICEs) revealed unique features: their chromosomal integration is totally random and driven by a DDE recombinase related to the Mutator-like superfamily. Mycoplasma conjugation is not restricted to ICE transmission, but also involves the transfer of large chromosomal fragments that generates progenies with mosaic genomes, nearly every position of chromosome being mobile. Mycoplasmas have thus developed efficient ways to gain access to a considerable reservoir of genetic resources distributed among a vast number of species expanding the concept of minimal cell to the broader context of flowing information.
类菌质体（俗称支原体）是由缺乏细胞壁、基因组较小的细菌组成的，其进化长期以来被认为仅仅是由基因丢失驱动的。最近大量的种内和种间水平基因转移（HGT）的证据为理解这些最小细菌对广泛宿主的成功适应提供了一个新的框架。越来越多的支原体物种中正在鉴定出移动遗传元件，但整合和共轭元件（ICEs）正在成为 HGT 的关键。虽然与其他细菌 ICEs 具有共同的特征，如染色体整合和使用 IV 型分泌系统介导水平传播，但支原体 ICEs（MICEs）表现出独特的特征：它们的染色体整合是完全随机的，由与 Mutator-like 超家族相关的 DDE 重组酶驱动。支原体的接合不仅限于 ICE 的传递，还涉及到大片段染色体的转移，这些转移产生了马赛克基因组的后代，几乎染色体的每一个位置都是可移动的。因此，支原体已经发展出有效的方法来获取广泛分布在大量物种中的大量遗传资源，从而将最小细胞的概念扩展到更广泛的信息流背景中。
