Physical mechanisms in the invasion of Lyme disease bacteria from fluids to tissue

This project will reveal the physical mechanisms that Borrelia burgdorferi (the bacterium that causes Lyme disease) uses to invade from liquid environments into tissue-like environments, which is crucial in many steps during the pathogenesis of Lyme disease (a disease which is estimated to affect about 476,000 people per year in the US). The PI will build off recent observations made by his group that find that this invasion may require the concerted effort of multiple individual bacteria to accomplish and their finding that Borrelia form dense clusters near the liquid/tissue interface. These clusters move toward the interface, bind to it, and then bacteria start entering in the tissue-like region. In addition, they did not observe individual bacteria moving into the tissue-like region by themselves, meaning that the bacteria use their collective behavior for the invasion. The project will shed light on how these clusters form, the fluid-cluster interactions that drive these clusters to the liquid tissue interface, and the resulting dynamics that facilitate the entry of the bacteria into the tissue-like region. In addition, the research will also explore whether B. burgdorferi utilizes mechano-sensing to move through tissue. During the pathogenesis of Lyme disease there are multiple steps that require Borrelia to move from a liquid into a tissue, such as migration out of the tick midgut, movement from the hemolymph into the tick salivary gland, and then from the feeding pit into the mammalian dermis. The work here will elucidate the physical mechanisms by which this occurs and could suggest novel therapeutics to prevent one or more of these steps. Third, Borrelia is part of the spirochete group of bacteria, which includes many other related pathogenic species, such as Treponema pallidum (causing syphilis) and Leptospira interrogans (causing leptospirosis). B. burgdorferi is one of the most invasive bacteria for mammalian hosts, being able to easily move through the dermis, into and out of blood vessels, into organs and tendons, and can even cross the blood brain barrier. The physical mechanisms by which the invasion occurs have been largely unstudied. This project uses a novel motility assay developed in the PI’s group to study how these bacteria move from liquid into a tissue or gel-like environment. Preliminary data shows that this involves a novel collective motility where the bacteria cluster together at the liquid/gel interface to facilitate the entry of individual bacteria into the tissue. The project will quantify the physical processes that occur, starting from the cluster formation through the entry of bacteria into the gel environment. In addition, using currently available Borrelia mutants the PI will also identify genes or groups of genes that are involved in this process. The final objective of the project will determine if Borrelia use mechano-sensing while migrating through tissue to navigate to high stress regions like tendons and the heart valve. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.