Unravelling tripartite species co-evolution under environmental change: can prophages accelerate bacterial virulence evolution?

两个相互作用的物种之间的适应和反适应可以非常快，使物种相互作用成为研究当代时间尺度上快速相互适应的理想选择。虽然理论模型和实证研究都涉及双重相互作用，但包括两个以上物种相互作用的数据很少。然而，在自然情况下，大多数（如果不是所有）物种与一个以上的物种相互作用。此外，人为影响正在改变选择制度，对物种相互作用产生广泛影响。因此，迫切需要在一个适当的背景下研究所有相关物种和非生物因素参与的物种相互作用。在第一阶段，我们建议使用由海龙组成的模型系统研究宿主-寄生虫三向相互作用中的快速进化适应（即最终的动物宿主），弧菌属的细菌，及其相关的温带弧菌（即感染弧菌细菌的小病毒）。由于能够整合到细菌基因组中，温和噬菌体成为可以提供其细菌宿主的前噬菌体（然后被称为溶原菌）与有益基因，例如可能增加细菌基因组可塑性并最终增加细菌适应性的毒力基因。在第一阶段，我们可以证明环境变化，例如降低的并因此造成压力的盐度条件改变了感染动力学以及细菌和温带细菌之间的共同进化轨迹。利用弧菌属和温带噬菌体之间的共同进化实验，我们观察到细菌对噬菌体的抗性进化方面的快速适应。在胁迫盐度下溶原菌优于噬菌体抗性突变体，我们现在建议（1）对从这些种群中选择的溶原菌和突变体进行全基因组测序，以确定潜在的基因组变化和原噬菌体整合到细菌染色体中的机制（随机对位点特异性），并且细菌通过其依赖于环境变化而进化出对温带细菌的抗性。（2）研究真核宿主及其免疫系统如何抑制或促进弧菌-噬菌体协同进化，以及如何最终加速弧菌毒力进化。为此，我们将使用两个不同的连续传代实验，其中我们跟踪真核宿主内的噬菌体-细菌共进化。所获得的结果将揭示细菌和温带细菌之间共同进化过程的基本机制，并将为快速毒力进化以及如何通过原噬菌体和环境变化加速毒力进化提供新的见解。

Adaptation and counter-adaptation between two interacting species can be very fast, making species interactions ideal to study rapid coadaptation on contemporary time scales. While both theoretical models and empirical studies deal with dual interactions, data including interactions of more than two species are scarce. However, in a natural scenario, most if not all species interact with more than one species. In addition, anthropogenic influences are changing selection regimes with broad implications on species interactions. Therefore, studies that address species interactions in an appropriate context with all relevant species and abiotic factors involved are urgently needed.During phase I we suggested studying rapid evolutionary adaptation in a three-way host-parasite interaction using an established model system consisting of pipefish Syngnathus typhle (i.e the final animal host), bacteria of the genus Vibrio, and it’s associated temperate phages (i.e. small viruses that infect Vibrio bacteria). With the ability to integrate into the bacterial genome, a temperate phage becomes a prophage that can provide its bacterial host (which is then called a lysogen) with beneficial genes, for instance virulence genes that may increase bacterial genome plasticity and ultimately bacterial fitness.During phase I we could demonstrate that environmental changes, such as reduced and thus stressful salinity conditions alter infection dynamics as well as co-evolutionary trajectories between bacteria and temperate phages. Using a co-evolution experiment between Vibrio sp. and a temperate phage we observed rapid adaptation in terms of bacterial resistance evolution against the phage. At stressful salinities lysogens were favoured over phage resistant mutants, whereas at ambient salinities lysogens were too costly and rapidly went extinct.We now propose (1) to perform whole genome sequencing on selected lysogens and mutants from those populations to identify the underlying genomic changes and mechanisms by which prophages integrate into the bacterial chromosome (random vs. site specific) and by which bacteria evolve resistance against temperate phages in dependence of environmental change. And (2) to investigate how an additional biotic interaction partner, the eukaryotic host and its immune system might constrain or promote Vibrio-phage co-evolution, and how it may ultimately accelerate Vibrio virulence evolution. To do so, we will use two different serial passage experiments, in which we follow phage-bacteria co-evolution inside the eukaryotic host. The obtained results will unravel basic mechanisms underlying co-evolutionary processes between bacteria and temperate phages and will provide novel insights into rapid virulence evolution and how it is accelerated by prophages and environmental change.