A putative xanthine dehydrogenase is critical for survival in ticks and mice.

is a pathogenic bacterium and the causative agent of Lyme disease. It is exposed to reactive oxygen species (ROS) in both the vertebrate and tick hosts. While some mechanisms by which ameliorates the effects of ROS exposure have been studied, there are likely other unknown mechanisms of ROS neutralization that contribute to virulence. Here, we follow up on a three gene cluster of unknown function, and that our prior unbiased transposon insertional sequencing studies implicated in both ROS survival and survival in . We confirmed these findings through genetic knockout and provide evidence that these genes are co-transcribed as an operon to produce a xanthine dehydrogenase. In agreement with these results, we found that exposure to either uric acid (a product of xanthine dehydrogenase) or allopurinol (an inhibitor of xanthine dehydrogenase) could modulate sensitivity to ROS in a dependent manner. Together, this study identifies a previously uncharacterized three gene operon in as encoding a putative xanthine dehydrogenase critical for virulence. We propose renaming this locus .