Borrelia burgdorferi, the spirochete agent of
Lyme disease, has evolved within a consistent infectious cycle between tick and vertebrate hosts. The transmission of the pathogen from tick to vertebrate is characterized by rapid replication and a change in the outer
surface protein profile.
EbfC, a highly conserved nucleoid-associated
protein, binds throughout the borrelial genome, affecting expression of many genes, including the Erp outer
surface proteins. In B. burgdorferi, like many other bacterial species,
ebfC is cotranscribed with dnaX, an essential component of the
DNA polymerase III holoenzyme, which facilitates chromosomal replication. The expression of the dnaX-
ebfC operon is tied to the spirochete's replication rate, but the underlying mechanism for this connection was unknown. In this work, we provide evidence that the expression of dnaX-
ebfC is controlled by direct interactions of DnaA, the chromosomal replication initiator, and
EbfC at the unusually long dnaX-
ebfC 5' untranslated region (UTR). Both
proteins bind to the
5' UTR DNA, with
EbfC also binding to the
RNA. The
DNA binding of DnaA to this region was similarly impacted by
ATP and
ADP. In vitro studies characterized DnaA as an activator of dnaX-
ebfC and
EbfC as an antiactivator. We further found evidence that DnaA may regulate other genes essential for replication. IMPORTANCE The dual life cycle of Borrelia burgdorferi, the causative agent of
Lyme disease, is characterized by periods of rapid and slowed replication. The expression patterns of many of the spirochete's
virulence factors are impacted by these changes in replication rates. The connection between replication and virulence can be understood at the dnaX-
ebfC operon. DnaX is an essential component of the
DNA polymerase III holoenzyme, which replicates the chromosome.
EbfC is a nucleoid-associated
protein that regulates the
infection-associated outer surface Erp
proteins, as well as other transcripts. The expression of dnaX-
ebfC is tied to replication rate, which we demonstrate is mediated by DnaA, the master chromosomal initiator
protein and
transcription factor, and
EbfC.