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

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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).