Department of Fundamental Microbiology, University of Lausanne, Lausanne, Switzerland.
PLoS Genet. 2022 Jun 28;18(6):e1010286. doi: 10.1371/journal.pgen.1010286. eCollection 2022 Jun.
The mechanisms and impact of horizontal gene transfer processes to distribute gene functions with potential adaptive benefit among prokaryotes have been well documented. In contrast, little is known about the life-style of mobile elements mediating horizontal gene transfer, whereas this is the ultimate determinant for their transfer fitness. Here, we investigate the life-style of an integrative and conjugative element (ICE) within the genus Pseudomonas that is a model for a widespread family transmitting genes for xenobiotic compound metabolism and antibiotic resistances. Previous work showed bimodal ICE activation, but by using single cell time-lapse microscopy coupled to combinations of chromosomally integrated single copy ICE promoter-driven fluorescence reporters, RNA sequencing and mutant analysis, we now describe the complete regulon leading to the arisal of differentiated dedicated transfer competent cells. The regulon encompasses at least three regulatory nodes and five (possibly six) further conserved gene clusters on the ICE that all become expressed under stationary phase conditions. Time-lapse microscopy indicated expression of two regulatory nodes (i.e., bisR and alpA-bisDC) to precede that of the other clusters. Notably, expression of all clusters except of bisR was confined to the same cell subpopulation, and was dependent on the same key ICE regulatory factors. The ICE thus only transfers from a small fraction of cells in a population, with an estimated proportion of between 1.7-4%, which express various components of a dedicated transfer competence program imposed by the ICE, and form the centerpiece of ICE conjugation. The components mediating transfer competence are widely conserved, underscoring their selected fitness for efficient transfer of this class of mobile elements.
水平基因转移过程的机制和影响已被充分证明，这些过程可以在原核生物中分配具有潜在适应性益处的基因功能。相比之下，对于介导水平基因转移的移动元件的生活方式知之甚少，而这是它们转移适应性的最终决定因素。在这里，我们研究了假单胞菌属内一种整合和共轭元件（ICE）的生活方式，该元件是一种广泛传播的家族的模型，可传递用于异生物质化合物代谢和抗生素抗性的基因。先前的工作表明 ICE 的激活具有双峰模式，但通过使用单细胞延时显微镜结合染色体整合的单个拷贝 ICE 启动子驱动的荧光报告基因、RNA 测序和突变分析，我们现在描述了导致分化的专用转移细胞出现的完整调控子。该调控子至少包含三个调控节点和 ICE 上的五个（可能是六个）进一步保守的基因簇，这些基因簇在静止期条件下均会表达。延时显微镜分析表明，两个调控节点（即 bisR 和 alpA-bisDC）的表达先于其他簇的表达。值得注意的是，除 bisR 外，所有簇的表达都局限于相同的细胞亚群，并且依赖于相同的关键 ICE 调节因子。因此，ICE 仅从群体中的一小部分细胞中转移，估计比例在 1.7-4%之间，这些细胞表达由 ICE 施加的专门转移能力程序的各种组件，并构成 ICE conjugation 的核心。介导转移能力的组件广泛保守，强调了它们对这类移动元件高效转移的选择适应性。
