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，这使得物种相互作用成为在当代时间尺度上研究快速共同适应的理想选择。虽然理论模型和经验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，大多数物种(如果不是所有物种)都与不止一个物种相互作用。此外，人为影响正在改变选择制度，对物种间的相互作用有着广泛的影响。因此，迫切需要在适当的背景下研究物种与所有相关物种和所涉及的非生物因素的相互作用。在阶段I中，我们建议使用一个已建立的模型系统来研究宿主-寄生虫三向相互作用中的快速进化适应，该模型系统由管状突触藻(即最终的动物宿主)、弧菌属细菌及其相关的温带噬菌体(即感染弧菌的小病毒)组成。由于能够整合到细菌基因组中，温带噬菌体成为一种前驱体，可以为其细菌宿主(当时被称为溶原体)提供有益的基因，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，如降低的应激盐度条件改变了感染动态以及细菌和温带噬菌体之间的共同进化轨迹。利用弧菌之间的共同进化实验。和一个温带噬菌体，我们观察到细菌对该噬菌体的抵抗力进化迅速适应。在有压力的盐度下，溶原体比抗噬菌体突变体更受青睐，而在环境盐度下，溶原体成本太高，而且很快就会灭绝。我们现在建议(1)对这些种群中选定的溶原体和突变体进行全基因组测序，以确定潜在的基因组变化和前驱噬菌体整合到细菌染色体(随机和位点特定的)以及细菌根据环境变化进化对温带噬菌体的抗性的机制。以及(2)研究额外的生物相互作用伙伴、真核宿主及其免疫系统如何限制或促进弧菌噬菌体的共同进化，以及它如何最终加速弧菌毒力进化。为此，我们将使用两个不同的系列传代实验，在其中我们跟踪噬菌体-细菌在真核宿主内的共同进化。所获得的结果将揭开细菌和温带噬菌体之间共同进化过程的基本机制，并将为快速毒力进化以及前驱体和环境变化如何加速其进化提供新的见解。

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.