National Reference Laboratory for Campylobacter, Department Biological Safety, Federal Institute for Risk Assessment (BfR), Diedersdorfer Weg 1, 12277, Berlin, Germany.
Institute of Molecular Biosciences, University of Graz, Humboldtstrasse 50, 8010, Graz, Austria.
Curr Top Microbiol Immunol. 2017;413:61-92. doi: 10.1007/978-3-319-75241-9_3.
Besides transduction via bacteriophages natural transformation and bacterial conjugation are the most important mechanisms driving bacterial evolution and horizontal gene spread. Conjugation systems have evolved in eubacteria and archaea. In Gram-positive and Gram-negative bacteria, cell-to-cell DNA transport is typically facilitated by a type IV secretion system (T4SS). T4SSs also mediate uptake of free DNA in Helicobacter pylori, while most transformable bacteria use a type II secretion/type IV pilus system. In this chapter, we focus on how and when bacteria "decide" that such a DNA transport apparatus is to be expressed and assembled in a cell that becomes competent. Development of DNA uptake competence and DNA transfer competence is driven by a variety of stimuli and often involves intricate regulatory networks leading to dramatic changes in gene expression patterns and bacterial physiology. In both cases, genetically homogeneous populations generate a distinct subpopulation that is competent for DNA uptake or DNA transfer or might uniformly switch into competent state. Phenotypic conversion from one state to the other can rely on bistable genetic networks that are activated stochastically with the integration of external signaling molecules. In addition, we discuss principles of DNA uptake processes in naturally transformable bacteria and intend to understand the exceptional use of a T4SS for DNA import in the gastric pathogen H. pylori. Realizing the events that trigger developmental transformation into competence within a bacterial population will eventually help to create novel and effective therapies against the transmission of antibiotic resistances among pathogens.
除了噬菌体转导，自然转化和细菌接合是驱动细菌进化和水平基因传播的最重要机制。接合系统在真细菌和古细菌中进化。在革兰氏阳性菌和革兰氏阴性菌中，细胞间的 DNA 运输通常由 IV 型分泌系统（T4SS）介导。T4SS 还介导幽门螺杆菌中游离 DNA 的摄取，而大多数可转化细菌使用 II 型分泌/IV 型菌毛系统。在本章中，我们重点讨论细菌如何以及何时“决定”在一个成为感受态的细胞中表达和组装这种 DNA 转运装置。DNA 摄取能力和 DNA 转移能力的发展是由各种刺激驱动的，通常涉及复杂的调控网络，导致基因表达模式和细菌生理学的巨大变化。在这两种情况下，遗传同质的群体产生一个独特的亚群，该亚群能够摄取 DNA 或进行 DNA 转移，或者可能均匀地转换为感受态。从一种状态到另一种状态的表型转换可以依赖于双稳态遗传网络，这些网络通过整合外部信号分子而随机激活。此外，我们还讨论了自然转化细菌中 DNA 摄取过程的原理，并旨在理解 T4SS 在胃病原体 H. pylori 中用于 DNA 输入的特殊用途。了解触发细菌群体中向感受态发育转化的事件最终将有助于创造针对病原体中抗生素耐药性传播的新型有效疗法。
