Abstract
The Lyme disease pathogen Borrelia burgdorferi responds to changes in the environment, including changes in nutrient availability and pH, throughout its enzootic lifecycle in Ixodes spp. ticks and vertebrate hosts. This project examined the role of the transcriptional regulator DnaK suppressor protein (DksA) in B. burgdorferi responses to environmental changes associated with its lifecycle. The role of DksA in regulating transcriptional responses of B. burgdorferi in a nutrient starved environment was assayed by microarray. Transcriptional analyses of wild-type and dksA-mutant B. burgdorferi revealed that DksA was likely required for global downregulation of genes encoding flagellar components, ribosomal proteins, and DNA replication machinery in response to starvation. An in vitro transcription assay developed with the RNA polymerase extracted from B. burgdorferi determined DksA inhibited transcription from RpoD-dependent flagellar and ribosomal promoters that are highly expressed, demonstrating the role of DksA in transcriptional regulation. The regulation of DksA and regulatory molecule guanosine tetraphosphate (ppGpp) were tested in a culture environment mimicking the tick midgut to understand their potential regulatory role. DksA levels were reduced in pH 6.8 culture mimicking the tick environment, while ppGpp levels became elevated. The presence of DksA was also conditional for the expression of infection associated lipoproteins in pH 6.8 culture. The requirement of DksA to complete the vector-host infection model was tested. Strains lacking DksA were unable to infect mice, however, DksA was unnecessary for long term survival in I. scapularis. Together, these results indicate that DksA direct the transcriptional responses required for B. burgdorferi to transition from the tick midgut environment to the mammalian host environment.