Relapsing fever (RF), caused by Borrelia spirochetes, is a globally distributed vector-borne disease and among the most common bacterial infections in some African countries. During the enzootic cycles of RF Borrelia, the bacteria transition between the disparate environments in the louse or tick vector and the mammalian host. To survive in these distinct environments, the bacteria must recognize environmental cues and modulate gene expression/protein production accordingly. A known environmental cue that Borrelia responds to by altering gene expression/protein production is temperature; at mammalian body temperature (37°C), known virulence factors are produced, whereas, at ambient temperature (23°C), vector colonization factors are produced. Seeking to exploit temperature-dependent changes in protein production to identify potential virulence factors (i.e., proteins with increased production at 37°C relative to 23°C), we performed a proteomic analysis of the tick-borne RF spirochete, Borrelia turicatae, cultured at these two temperatures. The projects presented within this dissertation aimed to characterize the role of two proteins potentially important for mammalian infection by B. turicatae based on these proteomic results. In the first project, the gene encoding BtpA, a protease only produced at 37°C, was inactivated to assess a potential function during infection. While the btpA mutant exhibited increased susceptibility to oxidative stress in vitro, the mutant had no defect in a murine model of RF. In the second project, the gene encoding the borrelial diadenylate cyclase responsible for cyclic-di-AMP synthesis, CdaA, which was produced more than two-fold greater at 37°C relative to 23°C, was inactivated to assess its role during mammalian pathogenesis. The cdaA mutant was non-infectious in a murine model of RF and exhibited growth defects at altered osmolarity and in media lacking pyruvate, implicating CdaA in virulence, osmoregulation, and central metabolism. Furthermore, whole genome sequencing analyses and CdaA depletion experiments revealed that suppressor mutations are likely required for normal growth and physiology in the absence of CdaA in vitro. In all, these studies revealed that, while BtpA is dispensable for B. turicatae mammalian infection, CdaA is absolutely required. Importantly, these results further our understanding of virulence factors and signaling pathways required by RF spirochetes during infection.
|Advisor:||Blevins, Jon S.|
|Commitee:||Pechous, Roger D., Dings, Ruud P.M., Voth, Daniel E., Li, Lin-Xi X.|
|School:||University of Arkansas for Medical Sciences|
|Department:||Microbiology and Immunology|
|School Location:||United States -- Arkansas|
|Source:||DAI-A 82/6(E), Dissertation Abstracts International|
|Subjects:||Microbiology, African Studies, Pathology, Virology, Immunology, Genetics, Bioinformatics|
|Keywords:||Borrelia, BtpA, c-di-AMP, CdaA, Protease, Relapsing fever, Tick-borne illnesses|
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