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。扁虱是专职食血的节肢动物，它将最多种类的病原体传播给北美的家畜和人类。这些寄生节肢动物也是非致病细菌内共生体的宿主，这些内共生体被认为对它们的扁虱宿主是有益的(即互惠共生的)或无害的(即共生的)；然而，这一点仍有待测试。最近的研究表明，扁虱的免疫系统不仅针对病原菌，而且还调节内共生菌的数量。证明一些非致病细菌对其寄主具有负面影响将把对细菌内共生菌的功能作用的讨论转移到一个新的范式：即它们是寄生虫(即重寄生虫)的寄生虫。*我的学生和我将使用比较基因组和元基因组的方法来探索与变种革螨和安德森革螨微生物群中的细菌内共生菌有关的三个问题：谁在那里？他们在做什么？它们对寄主有何影响？这两种虱类在加拿大大草原上很常见，也是已知的病原菌传播媒介。然而，对构成变种假丝酵母和安德森假丝酵母微生物群的细菌内共生体的物种多样性或功能作用知之甚少。我们将鉴定和测定来自多个种群的扁虱中细菌的相对丰度，确定它们在扁虱体内的发生位置，确定哪些细菌物种是通过宫内传播的，寻找细菌之间的积极和消极关联，并确定细菌内共生菌的功能作用。我们将检验假设：(1)细菌内共生体的总丰度和相对丰度在两个物种之间以及来自不同种群的硬蜱之间存在差异；(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)微生物群中的一些成员是重寄生虫。*我的短期研究计划不同于大多数其他关于扁虱微生物群的研究。与其只关注病原菌或细菌群落的组成，我想了解扁虱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宿主的生存和寻找宿主的行为。这对硬蜱和硬虱传播疾病的生物防治具有实际应用价值。此外，这项建议代表了我的研究计划的合乎逻辑的进步，不仅是在科学调查方面，而且在多学科框架(寄生虫学、微生物学和分子生物学)的研究生和本科生(HQP)的培训方面也是如此。

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).**