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he bacterial agent of Lyme disease, Borrelia burgdorferi (B. burgdorferi), exists in an enzootic cycle by adapting to dissimilar mammalian and tick environments. The genetic elements necessary for host and vector adaptation are spread across a unique bacterial genome comprised of a linear chromosome and essential linear and circular plasmids. The promoter trap system, In Vivo Expression Technology (IVET), has been used to identify promoters of B. burgdorferi that are transcriptionally active specifically during infection of a murine host. However, an observed bottleneck effect of singular dominant clones over the duration of infection in mice prevented the application of this system to study promoters induced in a tick environment. In this study, we adapted a membrane-based in vitro feeding system as a novel method to infect the Ixodes scapularis, Ixodes ricinus, and Ixodes pacificus vector with B. burgdorferi. Once adapted for Ixodes spp. of ticks, we performed an IVET screen through an infected bloodmeal on the system with Ixodes scapularis nymphs. We further designed a Tick-Specific IVET system to identify tick-induced B. burgdorferi promoters. The screen yielded B. burgdorferi promoters that are specifically induced during tick infection and verified relative expression levels of select genes in ticks compared to in vitro expression using qRT-PCR. The results of our study demonstrate the potential of our developed in vitro tick feeding system to gain insight into the mechanisms of adaptive gene expression to the tick vector by Lyme disease Borrelia agents.
