Plasmid manipulation of bacterial gene regulatory networks

基因组测序显示，细菌经常在不同物种之间交换基因，通过允许其大跃进而不仅仅是逐渐积累微小的变化来加快进化。基因经常通过被称为质粒的环状DNA片段从一个细菌细胞传递到另一个细菌细胞。对于细菌细胞来说，获得一个质粒通常是昂贵的。然而，目前人们对这些健身成本的原因知之甚少。健身成本的一个可能原因是，质粒经常携带干扰细菌基因开启/关闭的基因，导致这些基因在错误的时间表达。在这个提案中，我们研究了一种常见的植物相关细菌，荧光假单胞菌，在这种情况下，获得一个质粒可以打开大约20%的细菌基因。我们的初步数据将这种基因破坏与一种广泛的全球调控途径Gac/RSM联系起来，该途径控制着许多不同细菌物种在慢性、生物膜形成的生活方式和急性毒力状态之间的切换。这提出了一种有趣的可能性，即获得质粒可能会重新编程Gac/RSM途径，影响不同细菌物种的关键毒力和竞争相关行为，包括重要的人类和植物病原体。在这个项目中，我们将首先揭开质粒扰乱细菌基因表达的分子机制。受这些实验结果的影响，我们将研究在复杂的植物相关环境中获得质粒的适合性成本和潜在好处，并测试质粒是否通过提高其在植物上生长的细菌种群中的传播速度而从扰乱Gac/RSM途径中受益。这些实验将为细菌进化中的一个基本过程提供新的线索，有助于理解自然群落中编码重要功能特征(包括抗生素耐药性)的基因的共享。

Genome sequencing has revealed that bacteria frequently exchange genes between species, speeding-up evolution by allowing it to proceed by big leaps rather than just the gradual accumulation of small changes. Genes often pass from one bacterial cell to another on circular pieces of DNA called plasmids. Acquiring a plasmid is typically costly to a bacterial cell. However, little is currently known about the causes of these fitness costs. One possible cause of fitness costs is that plasmids often carry genes that interfere with the switching on / off of bacterial genes causing these genes to be expressed at the wrong times. In the proposal, we investigate a common plant-associated bacterium, Pseudomonas fluorescens, where gaining a plasmid switches on around 20% of bacterial genes. Our preliminary data links this gene disruption to a widespread global regulatory pathway, Gac/Rsm, which controls the switch between chronic, biofilm-forming lifestyles and acute virulent states in many different bacterial species. This raises the intriguing possibility that plasmid-acquisition may reprogram the Gac/Rsm pathway, impacting key virulence- and competition-related behaviours in diverse bacterial species, including important human and plant pathogens. In this project, we will first unravel the molecular mechanism by which plasmids disrupt bacterial gene expression. Informed by the results of these experiments, we will examine the fitness costs and potential benefits of plasmid acquisition in complex plant-associated environments, and test whether the plasmid benefits from disrupting the Gac/Rsm pathway by boosting its rate of spread in bacterial populations growing on plants. These experiments will shed new light on a fundamental process in bacterial evolution, with relevance for understanding the sharing of genes encoding important functional traits (including antibiotic resistance) in natural communities.