Project Summary Lyme disease is caused by spirochetes in the Borrelia burgdorferi (Bb) complex that are transmitted to mammals through bites by ticks of the Ixodes genus. Ticks are obligate blood-feeders, and Ixodes acquires Bb while feeding on an infected mammalian host species. Bb successfully evades the immune systems of both the mammalian host and the tick vector to maintain the infection cycle. A key step in the tick phase of the infection cycle is the ability of Bb to adhere to Ixodes midgut epithelial cells. It has been known for many years that this interaction can be blocked by deletion of the gene for a single Bb outer membrane protein, OspA. Without OspA, Bb is quickly eliminated from the Ixodes midgut. However, despite a great deal of research effort, there is a not yet a complete picture of the molecular components of Bb cell adhesion to Ixodes midgut cells. The goal of this proposal is to expand the molecular description of the interaction between Bb and Ixodes cells. The first part of the proposal will examine the question of whether the host can be used to alter Bb metabolism of in a way that weakens its interaction with the vector midgut. Recent experiments show that when short chain fatty acids (SCFAs) are added to Bb cultured under tick midgut-like conditions, the Bb outer membrane is altered in a way that might weaken its interaction with tick midgut cells. This will be tested using naïve ticks feeding on Bb-infected mice with diet-induced SCFAs in their blood plasma, to find out if SFCAs reduce Bb acquisition by ticks. The second part of the proposal will examine a group of membrane-interacting proteins known as TULIP domain proteins. Five tick TULIP domain proteins were recently found to undergo large changes in expression when the ticks feed on Bb-infected mice. Is Bb exploiting the expression of these tick proteins to enhance its interaction with the tick midgut? The third part of the proposal will use new methods of membrane reconstitution, chemical crosslinking, and proteomic/lipidomic analysis to identify Bb-midgut adhesion molecules. If successful, the results of this research will provide new information about how to manipulate the host-vector-pathogen system to induce the vector to eliminate the pathogen before it is transmitted to the host. !