Molecular mechanisms of gene regulation in the Lyme disease spirochete Borrelia burgdorferi: It's all about growth.

摘要

The Lyme disease spirochete, Borrelia burgdorferi , is naturally maintained through cycles between tick vectors and vertebrate hosts. This requires that the pathogen is able to detect its location in both time and space of the tick-mouse infection cycle, and respond by producing the appropriate profile of proteins at each stage of the infection cycle. Early studies found that expression of OspC and Erp proteins can be stimulated in culture by shifting temperature from 23 to 34°C. This led to the hypothesis that B. burgdorferi senses environmental temperature to determine its location in the tick mammal infectious cycle. However, borreliae cultured at mammalian body temperature divide faster than do those cultured at ambient temperature. By dissociating environmental temperature from growth rate I provide evidence that support a new paradigm that B. burgdorferi actually responds to changes in its own replication rate. These studies lead to the investigation of BpaB and EbfC, two proteins hypothesized to regulate erp operons. In vivo and in vitro methods demonstrated that BpaB functions as a repressor of erp transcription, while EbfC functions as an anti-repressor.;Several lines of evidence indicated that EbfC performed additional cellular functions. EbfC-GFP fusion and transcriptomic analysis determined that EbfC is a nucleoid-associated protein, and as such, controls the production of over 50 different transcripts. ebfC expression was shown to be linked to dnaX, a subunit of DNA polymerase, further supporting the theory that EbfC production is linked to bacterial growth.;A third borrelial protein that binds erp Operator DNA was identified as Bpur. Bpur governs the expression of multiple targets both at the transcriptional and post-transcriptional levels. Further investigations uncovered a novel, posttranscriptional self-riboregulation mechanism. Since Bpur acted as a global regulator, and its production was regulated, I reasoned that dysregulation would impact vertebrate infection. Indeed, ectopic over production of Bpur caused severe impairment in a murine infection model.;These studies highlight the need for bacterial pathogens to implicitly regulate their protein production. Also, the implication for metabolic status as an internal rheostat to control production of virulence factors is discussed as a general mechanism used throughout the domain Eubacteria.;KEYWORDS: Lyme Disease, Borrelia burgdorferi, Erp Proteins, Transcriptional regulation, nucleic acid-binding protein.