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The etiologic agent of Lyme disease, Borrelia burgdorferi, must adapt to the distinct environments of its arthropod vector and mammalian host during its complex life cycle. B. burgdorferi alters gene expression and protein synthesis in response to temperature, pH, and other uncharacterized environmental factors. The hypothesis tested in this study is that dissolved gases, including C[O.sub.2], serve as a signal for B. burgdorferi to alter protein production and gene expression. In this study we focused on characterization of in vitro anaerobic (5% C[O.sub.2], 3% [H.sub.2], 0.087 ppm [O.sub.2]) and microaerophilic (1% C[O.sub.2], 3.48 ppm [O.sub.2]) growth conditions and how they modulate protein synthesis and gene expression in B. burgdorferi. Higher levels of several immunoreactive proteins, including BosR, NapA, DbpA, OspC, BBK32, and RpoS, were synthesized under anaerobic conditions. Previous studies demonstrated that lower levels of NapA were produced when microaerophilic cultures were purged with nitrogen gas to displace oxygen and C[O.sub.2]. In this study we identified C[O.sub.2] as a factor contributing to the observed change in NapA synthesis. Specifically, a reduction in the level of dissolved C[O.sub.2], independent of [O.sub.2] levels, resulted in reduced NapA synthesis. BosR, DbpA, OspC, and RpoS synthesis was also decreased with the displacement of C[O.sub.2]. Quantitative reverse transcription-PCR indicated that the levels of the dbpA, ospC, and BBK32 transcripts are increased in the presence of C[O.sub.2], indicating that these putative borrelial virulence determinants are regulated at the transcriptional level. Thus, dissolved C[O.sub.2] may be an additional cue for borrelial host adaptation and gene regulation.

The etiologic agent of Lyme disease, Borrelia burgdorferi, must adapt to the distinct environments of its arthropod vector and mammalian host during its complex life cycle. B. burgdorferi alters gene expression and protein synthesis in response to temperature, pH, and other uncharacterized environmental factors. The hypothesis tested in this study is that dissolved gases, including CO2, serve as a signal for B. burgdorferi to alter protein production and gene expression. In this study we focused on characterization of in vitro anaerobic (5% CO2, 3% H2, 0.087 ppm O2) and microaerophilic (1% CO2, 3.48 ppm O2) growth conditions and how they modulate protein synthesis and gene expression in B. burgdorferi. Higher levels of several immunoreactive proteins, including BosR, NapA, DbpA, OspC, BBK32, and RpoS, were synthesized under anaerobic conditions. Previous studies demonstrated that lower levels of NapA were produced when microaerophilic cultures were purged with nitrogen gas to displace oxygen and CO2. In this study we identified CO2 as a factor contributing to the observed change in NapA synthesis. Specifically, a reduction in the level of dissolved CO2, independent of O2 levels, resulted in reduced NapA synthesis. BosR, DbpA, OspC, and RpoS synthesis was also decreased with the displacement of CO2. Quantitative reverse transcription-PCR indicated that the levels of the dbpA, ospC, and BBK32 transcripts are increased in the presence of CO2, indicating that these putative borrelial virulence determinants are regulated at the transcriptional level. Thus, dissolved CO2 may be an additional cue for borrelial host adaptation and gene regulation. [ABSTRACT FROM AUTHOR]