Identifying Factors Controlling Cell Shape and Virulence Gene Expression in Borrelia Burgdorferi

Abstract

Lyme disease is a multi-system inflammatory disorder that is currently the fastest growing arthropod-borne disease in the United States. The Lyme disease pathogen, Borrelia burgdorferi, exists within an enzootic cycle consisting of Ixodes tick vectors and a variety of vertebrate hosts. Borrelia lies within a distinct clade of microorganisms known as spirochetes which exhibit a unique spiral morphology. The underlying genetic mechanisms controlling for borrelial morphologies are still being discovered. One flagellar protein, FlaB, has been indicated to affect both spiral shape and motility of the organisms and significantly impacts the organism’s ability to establish infection. Due to the potential connection between morphological characteristics and pathogenesis, we sought to screen and identify morphological mutants in an attempt to identify genes associated with morphological phenotypes of Borrelia burgdorferi. Among Borrelia’s unique features is the presence of abundant lipoproteins making up its cellular membrane as opposed to the typical lipopolysaccharides. These proteins confer a wide variety of functions to the microorganism, among which include the abilities to circulate between widely differing hosts and to establish infection. Two important outer surface proteins, OspC and OspA, are found to be inversely expressed throughout the borrelial life cycle. OspC, in particular, becomes highly expressed during tick-feeding and transmission to the mammalian host. It has been found to be essential for establishment of infection. A global regulatory pathway has been shown to control for OspC, however there are missing links in this pathway between the external stimuli (such as temperature, pH, and cell density) and the regulatory pathway. We have performed a screening process to identify OspC expression mutants in order to identify novel genes associated with this pathway.