Tick microbiomes; are endosymbiotic bacteria mutualists, commensals or hyperparasites?

基因组学的进步为研究节肢动物的微生物群（即微生物群落）提供了令人兴奋的机会。蜱是专性吸血节肢动物，在北美向家畜和人类传播各种各样的病原体。这些寄生节肢动物也是非致病性细菌内共生体的宿主，这些细菌内共生体被认为对蜱虫宿主有益（即共生）或无害（即共生）；然而，这还有待检验。最近的研究表明，蜱虫的免疫系统不仅针对致病菌，而且还调节内共生细菌的数量。证明一些非致病性细菌对其宿主蜱虫有负面影响，将把关于细菌内共生体功能作用的讨论转移到一个新的范式：即它们是寄生虫的寄生虫（即超寄生虫）。***我和我的学生将使用比较基因组学和宏基因组学的方法来探索与变异革螨和安德森革螨微生物组中的细菌内共生体有关的三个问题：谁在那里？他们在做什么？它们是如何影响宿主的？这两种蜱在加拿大大草原上很常见，是已知的致病菌载体。然而，人们对构成变异性D. variabilis和安德氏D. andersoni微生物组的细菌内共生体的物种多样性或功能作用知之甚少。我们将从多个种群中识别和确定蜱虫中细菌的相对丰度，确定它们在蜱虫体内的发生位置，确定哪些细菌种类是经卵巢传播的，寻找细菌之间的积极和消极联系，并确定细菌内共生体的功能作用。我们将检验以下假设：(1)两种蜱之间以及不同种群的蜱之间细菌内共生菌的总量和相对丰度存在差异；(2)细菌内共生体的丰度和组成影响宿主的行为和/或生存；(3)微生物组的一些成员是超寄生虫。***我的短期研究计划与大多数其他关于蜱虫微生物组的研究不同。与其仅仅关注致病菌或细菌群落的组成，我想了解蜱虫微生物群中细菌内共生体的组成和相对丰度的变化如何影响其蜱虫宿主的生存和寻找宿主的行为。这对蜱虫和蜱传疾病的生物防治具有实际应用价值。此外，这一提案代表了我的研究计划的逻辑进展，不仅在科学调查方面，而且在多学科框架下（寄生虫学，微生物学和分子生物学）培养研究生和本科生（HQP）

Advances in genomics provide exciting opportunities to study the microbiomes (i.e. microbial communities) of arthropods. Ticks, obligate blood-feeding arthropods, transmit the greatest variety of pathogenic agents to domestic animals and humans in North America. These parasitic arthropods are also hosts of non-pathogenic bacterial endosymbionts that are assumed to be beneficial (i.e. mutualists) or of no harm (i.e. commensals) to their tick host; however, this remains to be tested. Recent studies show that a tick's immune system not only targets pathogenic bacteria but also regulates the numbers of endosymbiotic bacteria. Demonstrating that some non-pathogenic bacteria have a negative effect on their tick host would shift discussion on the functional roles of bacterial endosymbionts to a new paradigm: that is, they are parasites of a parasite (i.e. hyperparasites).***My students and I will use comparative genomic and metagenomic approaches to explore three questions relating to the bacterial endosymbionts within the microbiomes of Dermacentor variabilis and Dermacentor andersoni: who is there?, what are they doing? and how do they affect their host? Both tick species are common on the Canadian prairies and are known vectors of pathogenic bacteria. However, little is known of the species diversity or functional roles of the bacterial endosymbionts that comprise the microbiomes of D. variabilis and D. andersoni. We will identify and determine the relative abundance of bacteria in ticks from multiple populations, establish where they occur within a tick's body, determine which bacterial species are transmitted transovarially, search for positive and negative associations among bacteria, and identify the functional roles of the bacterial endosymbionts. We will test the hypotheses that: (1) there are differences in the total and relative abundance of bacterial endosymbionts between the two tick species, and among ticks from different populations; (2) the abundance and composition of the bacterial endosymbionts affect host behaviour and/or survival; and (3) some members of the microbiome are hyperparasites. ***My short-term research plan differs from most other studies on tick microbiomes. Rather than focus solely on pathogenic bacteria or the composition of bacterial communities, I want to understanding how changes in composition and relative abundance of bacterial endosymbionts within the tick microbiome impact the survival and host-seeking behaviour of their tick hosts. This has practical applications for the biological control of ticks and tick-borne diseases. Furthermore, this proposal represents a logical progression of my research program, not only in terms of scientific investigation, but also in the training of graduate and undergraduate students (HQP) within a multidisciplinary framework (parasitology, microbiology & molecular biology).**