NSF-BSF: Ecological Implications and Evolutionary Dynamics of a Nascent Sodalis-allied symbiont in a Parasitoid Wasp.

这个NSF-BSF项目由美国犹他大学和以色列海法大学的科学家合作完成。它着重分析了寄生蜂和一种名为Sodalis的共生细菌之间的联系。我们星球上的许多昆虫都进化出了与苏打菌的关系，苏打菌经常为它们的昆虫宿主提供营养或其他好处，使它们能够在营养供应不足的条件下生存。本项目研究的拟寄生蜂具有迄今为止在自然界中发现的最新衍生的索达里斯共生。它提供了一个前所未有的机会来研究新兴共生关系的机制和进化基础，使用的技术包括实验室昆虫操作，细菌基因改造和基因组测序。它将对一种被称为退行性进化的现象产生重要的见解，在这种现象中，共生细菌（包括许多病原体）在宿主的限制下经历了剧烈的基因损失。值得注意的是，在这个项目中，Sodalis共生体的基因组正在经历称为插入序列元件的寄生遗传元件的增殖，这些元件复制并插入细菌基因中，导致基因功能的广泛破坏和丧失。这种增殖将通过实验进化和基因组测序进行研究。此外，它将提供对母体共生体传播过程的机制理解。更广泛的影响将集中在犹他州和海法的初中生和高中生的教育上，他们将了解寄生蜂的生物学和生物防治潜力，并将参与从当地环境中收集寄生蜂。来自许多不同科的昆虫，包括无数的生活方式和栖息地，与索达利属的共生细菌保持着长期的联系。在某些情况下，这些关联起源于远古，由此产生的Sodalis共生体表现出广泛的基因组退化，这是孤立和统一的共生生活方式的结果。基因组退化涉及突变的积累，这些突变使在宽松选择下进化的基因失活和侵蚀。对新生共生体基因组的研究表明，自利插入序列（IS）元件在其退化过程中起着重要作用。这些is -元件在宿主结合的早期阶段进行增殖，呈现出细菌基因失活的有效机制，并为缺失基因重组事件产生重复模板。该项目关注的是一种新生的Sodalis共生体，这种共生体与寄生蜂生活在一起，已经在实验室培养，并且可以进行基因操作。通过实验进化，我们将在体外和体内研究is元素增殖的机制基础和进化后果。值得注意的是，这种Sodalis共生体中的一些is元素获得了细菌基因，可能使它们能够抑制竞争元素的转位，从而促进is元素的“战争游戏”。这些基因在增殖过程中的作用将通过对共生体的遗传操作进行检查。遗传方法也将被用来确定垂直共生传播在这个系统中的细菌决定因素。总之，这些活动将为基因组退化的早期决定性阶段提供重要的新见解，增强我们对互惠和致病关联进化的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This NSF-BSF project is a collaboration between scientists at the University of Utah, USA and the University of Haifa, Israel. It focuses on analyzing the connection between parasitoid wasps and a symbiotic bacterium named Sodalis. Many insects on our planet have evolved associations with Sodalis bacteria which often produce nutrients or other benefits for their insect hosts, allowing them to persist under conditions in which nutrient availability is sub-optimal. The parasitoid wasp under study in this project has the most-recently derived Sodalis symbiosis yet discovered in nature. It provides an unprecedented opportunity to study the mechanistic and evolutionary bases of emerging symbiotic relationships using techniques including laboratory insect manipulation, bacterial genetic modification and genome sequencing. It will yield important insight into a phenomenon known as degenerative evolution, in which symbiotic bacteria (including many pathogens) undergo drastic gene loss in response to confinement in a host. Notably, the genome of the Sodalis symbiont in this project is undergoing proliferation of parasitic genetic elements called insertion sequence elements, that replicate and insert themselves into bacterial genes, causing extensive disruption and loss of gene functions. This proliferation will be studied using experimental evolution and genome sequencing. In addition, it will provide a mechanistic understanding of the process of maternal symbiont transmission. Broader impacts will focus on the education of middle and high school students in Utah and Haifa, who will learn about the biology and bio-control potential of parasitoids and will engage in the collection of parasitoids from their local environment. Insects from many different families, encompassing myriad lifestyles and habitats, maintain long-term associations with symbiotic bacteria of the genus Sodalis. In some cases, these associations are ancient in origin and the resulting Sodalis symbionts demonstrate extensive genome degeneration as a consequence of the isolated and uniform symbiotic lifestyle. Genome degeneration involves accumulation of mutations that inactivate and erode genes evolving under relaxed selection. Inspection of the genomes of nascent symbionts reveal that selfish insertion sequence (IS)-elements play an important role in the process of degeneration. These IS-elements undergo proliferation in the early-stages of host-association, presenting a potent mechanism for inactivation of bacterial genes and yielding repetitive templates for deletogenic recombination events. This project focuses on a nascent Sodalis symbiont that lives in association with a parasitoid wasp, has been cultured in the laboratory and is amenable to genetic manipulation. The mechanistic basis and evolutionary consequences of IS-element proliferation will be studied in vitro and in vivo using experimental evolution. Notably, some IS-elements in this Sodalis symbiont have acquired bacterial genes that likely enable them to silence the transposition of competing elements, facilitating IS-element “war games”. The role of these genes in the proliferation process will be examined via genetic manipulation of the symbionts. Genetic approaches will also be utilized to identify the bacterial determinants of vertical symbiont transmission in this system. Together, these activities will provide important new insight into the early, deterministic stages of genome degeneration, enhancing our understanding of the evolution of mutualistic and pathogenic associations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.