Regulation of Infection-Associated Protein Expression by the Lyme Disease Spirochete DnaA Protein

Vector-borne pathogens such as Borrelia burgdorferi, the agent of Lyme disease, produce different proteins during infection of the mammalian host and the arthropod vector. These include distinct surface proteins to interact with the variety of tissues that are encountered. In addition, vector-borne bacteria must sense when the vector is feeding on a host, and efficiently coordinate transmission processes. We discovered that several key infection-associated proteins that are produced during tick feeding and transmission can be induced in culture by increasing the rate of bacterial replication. A model proposes that this corresponds to the dramatic increase in growth rate of B. burgdorferi when a tick begins to feed on blood. We found that the master regulator of chromosomal replication, the DnaA protein, binds adjacent to the transcriptional promoters of loci that encode two global regulatory proteins. Both of those regulatory proteins direct the production of surface proteins that contribute to mammalian infection processes. DnaA homologs are known to regulate transcription in E. coli and other bacterial species. We hypothesize that DnaA serves to connect borrelial replication with production of infection-associated proteins. The planned studies will critically test that hypothesis by identifying DnaA-binding sites throughout the B. burgdorferi genome by chromatin immunoprecipitation - sequencing (ChIP-Seq), characterizing two new DnaA-regulated loci, and biochemically defining factors involved with DnaA-binding. Altogether, results of these studies will characterize a novel regulon of the Lyme disease spirochete, providing substantial new insight on the bacteria’s physiology and infectious mechanisms.