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

这个NSF-BSF项目是美国犹他州大学和以色列海法大学的科学家之间的合作。它的重点是分析寄生蜂和一种名为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Sodalis细菌的联系，这些细菌经常为其昆虫宿主产生营养或其他益处，使它们能够在营养可用性次优的条件下持续存在。 在这个项目中研究的寄生蜂具有在自然界中发现的最近衍生的Sodalis共生。它提供了一个前所未有的机会，研究新兴的共生关系的机制和进化基础，使用技术，包括实验室昆虫操纵，细菌遗传修饰和基因组测序。 它将对一种被称为退化进化的现象产生重要的洞察力，在这种现象中，共生细菌（包括许多病原体）在宿主中受到限制时会经历剧烈的基因丢失。 值得注意的是，该项目中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到细菌基因中，导致基因功能的广泛破坏和丧失。 将使用实验进化和基因组测序来研究这种增殖。 此外，它将提供一个机制的理解过程中的母体共生体的传输。 更广泛的影响将集中在犹他州和海法的中学生的教育上，他们将了解拟寄生虫的生物学和生物控制潜力，并将从事从当地环境中收集拟寄生虫的工作。来自许多不同科的昆虫，包括无数的生活方式和栖息地，与Sodalis属的共生细菌保持着长期的联系。在某些情况下，这些协会是古老的起源和所产生的Sodalis共生体表现出广泛的基因组退化作为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，这些突变破坏和侵蚀了在宽松选择下进化的基因。对新生共生体基因组的研究表明，自私插入序列（IS）元件在共生体的退化过程中起着重要的作用。这些IS元件在宿主结合的早期阶段进行增殖，呈现细菌基因失活的有效机制，并产生用于去基因重组事件的重复模板。该项目的重点是一个新生的Sodalis共生体，生活在与寄生蜂，已在实验室培养，并适合遗传操作。IS元件增殖的机制基础和进化后果将在体外和体内使用实验进化进行研究。值得注意的是，这种Sodalis共生体中的一些IS元件已经获得了细菌基因，这可能使它们能够沉默竞争元件的转座，从而促进IS元件的“战争游戏”。这些基因在增殖过程中的作用将通过共生体的遗传操作进行检查。遗传方法也将被用来确定在这个系统中的垂直共生体传输的细菌决定因素。总之，这些活动将为基因组退化的早期确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NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

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.