Date of Award

January 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

First Advisor

Catherine A. Brissette

Abstract

Borrelia burgdorferi is an enigmatic bacterial pathogen that afflicts a large proportion of the world population as the causative agent of Lyme disease. The bacterium has a number of factors that promote virulence including a complex and dynamic array of extracellular proteins that can interact with various molecules of an infected host. One such molecule, fibronectin, is a key glycoprotein in the ECM of mammalian hosts with multiple characterized functions. B. burgdorferi encodes multiple known Fn-binding proteins, and has an additional putative protein BB0347 that may also bind Fn. Another protein, MlpJ, is homologous to a known hemin-binding protein, which is curious, as iron, the element carried by the hemin molecule, is not essential for spirochete survival. In the included studies, we sought to characterize the function and importance of these two bacterial proteins, BB0347 and MlpJ, using various molecular, biochemical, and biomedical techniques. Such methods included the production and purification of recombinant proteins and corresponding antibodies; development of mutant B. burgdorferi strains, various immunohistochemical assays, and the infection of inbred laboratory mice and Ixodes ticks with virulent B. burgdorferi strains followed by subsequent molecular and culture-based analyzes of infected specimens. We verified that both proteins were surface exposed and capable of performing their hypothesized functions (Fn binding for BB0347 and hemin binding for MlpJ). In addition, BB0347 interacts with human

fibronectin via multiple domains, enhances the adherence capabilities of intact spirochetes, and allows for an increased bacterial load in various tissues at an early time point in the mouse infection model. Additionally, while MlpJ binds to the iron-containing molecule hemin, this interaction negatively affects bacterial survival in vitro after a hemin challenge but doesn’t impact bacterial fitness in the same mouse model at any of the times measured. Overall, we hope that advances made in these proteins may help further characterize the processes and dynamics of a human infection with B. burgdorferi, which may, in turn, lead to advances in treatment techniques for Lyme disease as well as other bacterial infections

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