Roles of reactive oxygen and nitrogen species on vector colonization by tick-borne relapsing fever spirochetes - PROJECT SUMMARY
Relapsing fever (RF) Borrelia are a major source of febrile illnesses globally causing significant morbidity and
mortality in children. Like other vector-borne pathogens, RF Borrelia must sense and adapt to diverse
environmental conditions as they colonize tissues of their arthropod vectors, and various mammalian hosts. Our
long-term goal is to develop novel control measures against RF spirochetes by elucidating the molecular
mechanisms of vector colonization and transmission. The objective of this proposal is to identify molecular events
essential for tick colonization by RF spirochetes. Currently, very little is known about the environmental
conditions RF Borrelia encounter within their soft-bodied tick vectors of the genus Ornithodoros, however, we
have recently shown that substantial amounts of reactive oxygen species (ROS) (e.g. O2•-, H2O2 and OH•) and
reactive nitrogen species (RNS) (e.g., NO, NO2•, N2O3 and ONOO-) are produced in the salivary glands and
midguts of Ornithodoros ticks. Our central hypothesis is that successful colonization of tick midgut and salivary
glands by B. turicatae is driven by changes in gene expression resulting from ROS and RNS-dependent redox
modifications to B. turicatae proteins. This hypothesis will be tested by pursuing two specific aims: 1) Determine
the impact of ROS and RNS produced by O. turicata ticks on B. turicatae gene expression; and 2) Characterize
the role of redox-active proteins in B. turicatae adaptation to oxidative and nitrosative environments within the
tick vector by biochemical analyses and mutagenesis. Under our first aim, we will employ already proven
approaches for measuring ROS and RNS production in O. turicata ticks, along with established approaches for
monitoring gene expression in both B. turicatae and O. turicata by RNAseq, droplet digital PCR, and RT-qPCR.
Under the second aim, we will use an innovative method to identify and quantify redox modifications to B.
turicatae proteins coupled with our established methods for characterizing the role of genes in B. turicatae
colonization of O. turicata ticks. The approach is innovative, because it departs from the status quo by focusing
on the molecular mechanisms driving adaptation of B. turicatae during colonization of O. turicata ticks. The
proposed research is significant, because it is expected to expand our understanding of how RF Borrelia sense
and adapt to the varied environments they encounter during infection. Ultimately, such knowledge has the
potential to inform the development of strategies to disrupt the natural cycle of infection for RF Borrelia or the
identification of novel vaccine targets that can be used to reduce RF infections.!
