Characterization of Borrelia burgdorferi erp gene regulatory systems: LuxS and EbfC

Lyme disease is a debilitating condition that affects thousands of people throughout the Northern hemisphere. The causative agent, Borrelia burgdorferi, is transmitted to humans by the bite of infected Ixodes ticks, so the bacterium has evolved mechanisms for infection of diverse hosts. In fact, the bacterium is able undergo extraordinary physiological adaptations within and while being transmitted from each host type. Of the many proteins that the bacterium induced within the mammal, the Erp family proteins have particular importance. The Erp proteins are surface-exposed antigens that have been shown to interact with various mammalian proteins. These inter-kingdom interactions are likely to contribute to the pathogenic process of the bacterium. Through the course of this dissertation research I have analyzed two independent methods whereby the bacterium interacts with its own erp genes. The results of this work have led to the characterization of two systems which affect not only the erp genes, but the general physiology of Borrelia burgdorferi.; The first mechanism that I characterized was cell-cell communication through the LuxS mediated quorum sensing system. This work demonstrated that B. burgdorferi possesses three genes in a single operon that directly connect common cellular methylation reactions to the production of the membrane diffusible signaling molecule, Al-2, and that this operon is induced in periods of rapid growth. This direct relationship between rate of methylation and production of an extracellular signaling molecule means that these bacteria possesses a method for community-wide analysis of methylation rate, and, therefore, total health of the community. The second mechanism for interaction with the bacterium's own erp genes is through a novel DNA-binding protein, EbfC. This study provided the first molecular characterization of this novel DNA-binding protein and its interactions with cognate DNA. The results of this work demonstrate that B. burgdorferi EbfC represents a new family of proteins with nucleoid-associated DNA-binding properties which are found throughout the eubacterial kingdom. These properties are shared among structural peptides of the nucleoid, and include being a small protein, with a simple binding sequence, non-specific binding, and multimerization.; Keywords: Borrelia burgdorferi, Lyme Disease, Erp Protein, Quorum Sensing, DNA-Binding Protein.