The Evolution of Bacterial Mutualism with Eukaryotic Hosts

细菌：朋友还是敌人？所有的植物和动物都与细菌有着某种形式的亲密关系。虽然我们经常关注导致疾病的有害细菌，但最近的研究表明，许多生活在动物体内的细菌实际上是有益的。无论这是生活在萤火虫体内的发光细菌，帮助它们吸引配偶到生活在我们肠道内的100万亿个细菌细胞，帮助消化，有益的微生物对地球上的所有生物都是永远存在的，也是重要的。我的研究探讨了动物如何与共生微生物形成有益的关系，并提出了以下问题：是什么因素使动物和微生物之间产生稳定的互利联盟，以及是什么原因导致这些关系破裂？为了回答这些问题，我集中在一组生物体上，它们与微生物，昆虫，进化出了迷人的关系。昆虫是多种共生微生物的宿主，这些微生物对昆虫的生物学有着深远的影响。这些作用包括，保护昆虫免受天敌，如寄生蜂和病原真菌，为昆虫提供保护以对抗热应激，并帮助昆虫获得营养。这些有益微生物的一个独特特征是，只有某些昆虫种群有它们，而其他昆虫没有。此外，只有某些细菌菌株为其昆虫宿主提供益处，而其他菌株则没有。这种自然变异提供了一个绝佳的机会来提出这样的问题：为什么某些昆虫宿主种群含有有益的微生物，而其他种群则没有？而且，为什么只有一些共生微生物为昆虫提供益处，以及有益功能的丧失如何影响它们与宿主的关系？为了回答这些问题，我使用现代DNA技术，使我能够在分子水平上识别影响有益微生物功能的因素，并探索数百万年来宿主-微生物关系的演变。将这些现代技术应用于昆虫细菌共生体中有趣的变异，使人们对所有植物和动物中维持和降低与细菌的有益关系的因素有了一个普遍的了解。宿主-微生物关系在自然界中无处不在，了解维持和降低这些关系的因素对农业和健康都有重要意义。我的研究不仅将为细菌有益性状的获得和丧失提供新的见解，而且在理解细菌病原体有害性状的获得和丧失方面也具有巨大的潜力。更直接的应用，我的研究可以导致管理农业害虫和那些主要的人类疾病的载体的实际解决方案。农药是对付害虫的常用解决方案，然而，减少农药使用以减轻我们对环境有害化学品的依赖的压力很大。许多昆虫害虫已经进化出与共生细菌的互利关系，例如传播恰加斯病的锥虫，传播昏睡病的采采蝇，使世界各地的作物枯萎的谷物象鼻虫，以及所有的汁液吸吮昆虫。利用细菌和昆虫宿主之间的关系进行害虫生物防治的研究，称为基于共生体的控制策略，由于减少了对环境的影响，是化学防治的首选策略。我的研究是推进我们对许多害虫物种中昆虫-细菌关系的理解的关键的第一步，通过揭示细菌和宿主相互作用的分子机制，以及促进细菌和宿主之间稳定关系的条件。这项研究的知识可用于帮助开发管理农业，林业和主要人类疾病媒介害虫的实用解决方案。

Bacteria: friend or foe?All plants and animals share some form of intimate relationship with bacteria. Although we often focus on harmful bacteria that cause diseases, recent research has shown that many bacteria that live within animals are actually beneficial. Whether this is the light-producing bacteria that live within fireflies that help them attract mates to the 100 trillion bacterial cells that live within our guts that aid in digestion, beneficial microbes are both ever-present and important to all organisms on the planet. My research explores how animals form beneficial relationships with symbiotic microbes by asking: What are the factors that produce stable mutually beneficial unions between animals and microbes, and what cause these relationships to break down? To answer these questions I focus on a single group of organisms that have evolved fascinating relationships with microbes, insects. Insects are host to a diverse community of symbiotic microbes that have profound effects on their biology. These effects include, protecting insects from natural enemies, such as parasitic wasp and pathogenic fungus, providing insects with protection against heat stress and assist insects in gaining nutrients. A peculiar feature of these helpful microbes is that only certain populations of insects have them, whereas others do not. In addition, only certain bacterial strains provide benefits to their insect hosts whereas others do not. This natural variation presents a perfect opportunity to ask questions such as: why do certain populations of insect hosts contain beneficial microbes whereas others do not? And, why do only some of the symbiotic microbes provide benefits to insects, and how does the loss of beneficial function impact their relationship with their host? To answer these questions I use modern DNA technology that allow me to identity factors that influence beneficial microbial functions at a molecular level, as well as explore the evolution of host-microbe relationships over millions of years. The application of these modern techniques to the intriguing variation in the bacterial symbionts of insects provides a general understanding of the factors that maintain and degrade beneficial relationships with bacteria in all plants and animals. Host-microbe relationships are everywhere in nature, and understanding the factors that maintain and degrade these relationships has important implications in both agriculture and health. My research will not only provide novel insight into the gain and loss of beneficial traits in bacteria, but also has great potential in understanding the gain and loss of harmful traits in bacterial pathogens. Of more immediate application, my research can lead to practical solutions for managing insect pests in agriculture and those that vector major human diseases. Pesticides were common solutions to deal with pests, however there is strong pressure to reduce pesticide use to moderate our reliance on environmental harmful chemicals. Many insect pests have evolved mutualistic relationships with symbiotic bacteria such as, Triatoma bugs that vector Chagas disease, tsetse fly that vector sleeping sickness, cereal weevils that devastates crops around the world, and all sap sucking insects. Research to exploit the relationship between bacteria and insect hosts for the biological control of pests, termed Symbiont-Based Control Strategies, is a preferred strategy to chemical control due to the reduced environmental impact. My research is a critical first step in advancing our understanding of insect-bacteria relationships in many pest species, by revealing both the molecular mechanisms by which bacteria and hosts interact, as well as the conditions that promote stable relationships between bacteria and host. The knowledge from this research can be used to help develop practical solutions for managing pests in agriculture, forestry and those that vector major human diseases.