The Lyme disease spirochete, Borrelia burgdorferi , persists in nature by alternatingly cycling between ticks and vertebrates. During each stage of the infectious cycle, B. burgdorferi produces surface proteins that are necessary for interactions with the tick or vertebrate tissues it encounters while also repressing the synthesis of unnecessary proteins.

No abstract

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.

Borrelia burgdorferi (sensu lato) requires its surface-exposed OspC protein in order to establish infection of humans and other vertebrate hosts. Lyme disease spirochetes initiate production of OspC when the vector tick begins to feed on the blood of a vertebrate host, and the spirochetes ceases production of OspC soon after establishment of infection. Bacteria that either do not produce OspC during transmission, or fail to repress OspC after infection is established, are rapidly cleared by the host. The molecular mechanisms controlling OspC production are largely unstudied. Herein, we identified a borrelial protein, Gac, that binds with high affinity to the ospC promoter and 5' adjacent DNA. A combination of biochemical analyses and investigations of genetically-manipulated bacteria demonstrated that Gac is a transcriptional repressor of ospC. This is a substantial advance toward understanding how the Lyme disease spirochete controls production of the essential OspC virulence factor, and identifies a novel target for preventative and curative therapies.

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 co-transcribed 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' UTR region. Both proteins bind to the 5' UTR DNA, with EbfC also binding to the RNA. The DNA binding of DnaA to this region was not impacted by ATP or ADP. In vitro studies characterized DnaA as an activator of dnaX-ebfC and EbfC as an anti-activator. We further found evidence that DnaA may regulate other genes essential for replication.