PROJECT SUMMARY Borrelia burgdorferi, the etiologic agent of Lyme disease, is a major source of illness in the United States with over 476,000 cases per year. Like other vector-borne pathogens, B. burgdorferi must overcome a wide variety of environmental stresses during its infectious cycle in ticks of the genus Ixodes, and various mammalian hosts. Among the challenges faced by B. burgdorferi are shifts in pH, temperature, osmolarity, nutrient availability, reactive oxygen species (ROS) along with nitric oxide (NO) and its congeners [reactive nitrogen species (RNS) (e.g., NO, NO2•, N2O3 and ONOO-)]. Of these, the roles of temperature and pH on B. burgdorferi virulence gene expression and infectivity have been the best characterized. Previously published work from our laboratory and others have demonstrated that B. burgdorferi encounters biologically significant amounts of ROS and RNS during infection of its tick vector Ixodes scapularis and mammalian hosts. We have also shown that cysteine thiols of proteins involved in gene regulation, antioxidant defenses, and central metabolism are targets of ROS and RNS, although the impact of these modifications on B. burgdorferi infectivity have yet to be determined. Our previously published work showed the DnaK suppressor protein (DksA) is a global regulator of gene expression in B. burgdorferi and coordinates the stringent response during periods of nutrient limitation. We now have preliminary data supporting a role for DksA in regulating virulence gene expression required for completion of its infectious cycle in I. scapularis and mammalian hosts. Despite this, there are substantial gaps in our knowledge about how DksA senses changes within its vector and mammalian hosts to direct B. burgdorferi gene expression. In this application, we propose to test our central hypothesis that DksA senses tick-borne ROS/RNS to coordinate the transcriptional responses of B. burgdorferi required for the completion of its infectious cycle. This proposal is particularly innovative and will impact the field of tick-borne diseases by determining the mechanisms underlying the ability of B. burgdorferi to sense changes in its environment to regulate gene expression. Since this area of research is virtually uninvestigated for tick-borne diseases, our findings will undoubtedly provide insight to the field and inform future strategies to prevent tick-borne infections.

NARRATIVE The Lyme disease spirochete Borrelia burgdorferi uses a small repertoire of gene regulatory proteins including the DnaK suppressor protein (DksA) to coordinate the expression of virulence genes required for the successful completion of its infectious cycle. This proposal is focused on characterizing how DksA senses tick-borne oxidants to direct B. burgdorferi virulence gene expression required for transmission by its tick vector Ixodes scapularis to mammalian hosts. With over 476,000 cases of Lyme disease each year, determining the molecular mechanisms underlying the ability of B. burgdorferi to complete its infectious cycle will enable the development of public health strategies to limit B. burgdorferi infections by disrupting the natural cycle of infection.