Identification of bptA (bbe16) as an Essential Gene for the Persistence of the Lyme Disease Spirochete, Borrelia Burgdorferi, in its Natural Tick Vector
Revel, Andrew Thomas
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Borrelia burgdorferi (B. burgdorferi), the agent of Lyme disease, is a zoonotic spirochetal bacterium that depends on both arthropod (Ixodes ticks) and ammalian (rodent) hosts for its persistence in nature. To more broadly survey B. burgdorferi's adaptive responses to these two diverse environmental niches, DNA microarrays were constructed and utilized to identify potential virulence factors contributing to B. burgdorferi's infectivity, pathogenesis, host range, and/or maintenance in its complex life cycle. Specifically, the microarray data provided a basis for formulating new testable hypotheses regarding the life cycle of B. burgdorferi. Recent advancements in borrelial genetics, some of which were developed in this study, provided us with the tools to genetically manipulate B. burgdorferi. Mutational analysis of two differentially regulated genes (bba36 and bbe16) targeted from microarray data was performed in an attempt to ascribe a function to each gene. Although no phenotype could be found for bba36, bbe16 was found to potentiate the virulence of B. burgdorferi in the mouse model of Lyme borreliosis and was essential for the persistence of B. burgdorferi in Ixodes scapularis ticks. As such, we have renamed bbe16 as a gene encoding borrelial persistence in ticks (bptA). Protease accessibility experiments indicated that BptA was a putative lipoprotein and was surface-exposed on the outer membrane of B. burgdorferi. Moreover, BptA also was shown to be highly conserved in all B. burgdorferi sensu lato strains tested, suggesting that BptA may be widely utilized by Lyme borreliosis spirochetes for persistence in nature. Given B. burgdorferi's absolute dependence on and intimate association with both its arthropod and mammalian hosts, this study has provided evidence that bptA is a virulence factor critical for B. burgdorferi's overall parasitic strategy.