Patterns and regulation of ribosomal RNA transcription in Borrelia burgdorferi

BACKGROUND: Borrelia burgdorferi contains one 16S and two tandem sets of 23S-5S ribosomal (r) RNA genes whose patterns of transcription and regulation are unknown but are likely to be critical for survival and persistence in its hosts. RESULTS: RT-PCR of B. burgdorferi N40 and B31 revealed three rRNA region transcripts: 16S rRNA-alanine transfer RNA (tRNA(Ala)); tRNA(Ile); and both sets of 23S-5S rRNA. At 34°C, there were no differences in growth rate or in accumulation of total protein, DNA and RNA in B31 cultured in Barbour-Stoenner-Kelly (BSK)-H whether rabbit serum was present or not. At 23°C, B31 grew more slowly in serum-containing BSK-H than at 34°C. DNA per cell was higher in cells in exponential as compared to stationary phase at either temperature; protein per cell was similar at both temperatures in both phases. Similar amounts of rRNA were produced in exponential phase at both temperatures, and rRNA was down-regulated in stationary phase at either temperature. Interestingly, a rel(Bbu )deletion mutant unable to generate (p)ppGpp did not down-regulate rRNA at transition to stationary phase in serum-containing BSK-H at 34°C, similar to the relaxed phenotype of E. coli relA mutants. CONCLUSIONS: We conclude that rRNA transcription in B. burgdorferi is complex and regulated both by growth phase and by the stringent response but not by temperature-modulated growth rate.