Department of Biology , University of York , York YO10 5GG , UK.
Department of Animal and Plant Sciences , University of Sheffield , Western Bank, Sheffield S10 2TN , UK.
R Soc Open Sci. 2016 Mar 23;3(3):150708. doi: 10.1098/rsos.150708. eCollection 2016 Mar.
Ancient evolutionary events are difficult to study because their current products are derived forms altered by millions of years of adaptation. The primary endosymbiotic event formed the first photosynthetic eukaryote resulting in both plants and algae, with vast consequences for life on Earth. The evolutionary time that passed since this event means the dominant mechanisms and changes that were required are obscured. Synthetic symbioses such as the novel interaction between Paramecium bursaria and the cyanobacterium Synechocystis PC6803, recently established in the laboratory, permit a unique window on the possible early trajectories of this critical evolutionary event. Here, we apply metabolic modelling, using flux balance analysis (FBA), to predict the metabolic adaptations necessary for this previously free-living symbiont to transition to the endosymbiotic niche. By enforcing reciprocal nutrient trading, we are able to predict the most efficient exchange nutrients for both host and symbiont. During the transition from free-living to obligate symbiosis, it is likely that the trading parameters will change over time, which leads in our model to discontinuous changes in the preferred exchange nutrients. Our results show the applicability of FBA modelling to ancient evolutionary transitions driven by metabolic exchanges, and predict how newly established endosymbioses, governed by conflict, will differ from a well-developed one that has reached a mutual-benefit state.
远古进化事件很难研究，因为它们的现存产物都是经过数百万年的适应改变而来的原始形式。最初的内共生事件形成了第一个光合作用的真核生物，导致了植物和藻类的产生，对地球上的生命产生了巨大的影响。自那次事件以来，经过了漫长的进化时间，主导机制和所需的变化已经变得模糊不清。像 Paramecium bursaria 和蓝藻 Synechocystis PC6803 之间的新型相互作用这样的合成共生关系，最近在实验室中建立，为研究这一关键进化事件的早期轨迹提供了独特的机会。在这里，我们应用代谢建模，使用通量平衡分析（FBA），来预测这个以前自由生活的共生体过渡到内共生环境所必需的代谢适应。通过强制互惠营养交换，我们能够预测宿主和共生体最有效的交换营养物质。在从自由生活到专性共生的过渡过程中，交易参数很可能随着时间的推移而发生变化，这导致我们的模型中，首选交换营养物质会发生不连续的变化。我们的研究结果表明，FBA 模型在代谢交换驱动的远古进化转变中具有适用性，并预测了由冲突控制的新建立的内共生体将如何与已经达到互利状态的成熟内共生体有所不同。
