Abstract
BackgroundIt has been shown previously that aminocoumarin antibiotics such as novobiocin lead to immediate downregulation of recA expression and thereby inhibit the SOS response, mutation frequency and recombination capacity in Staphylococcus aureus. Aminocoumarins function by inhibiting the ATPase activity of DNA gyrase subunit B with a severe impact on DNA supercoiling.ResultsHere, we have analysed the global impact of the DNA relaxing agent novobiocin on gene expression in S. aureus. Using a novobiocin-resistant mutant, it became evident that the change in recA expression is due to gyrase inhibition. Microarray analysis and northern blot hybridisation revealed that the expression levels of a distinct set of genes were increased (e.g., recF-gyrB-gyrA, the rib operon and the ure operon) or decreased (e.g., arlRS, recA, lukA, hlgC and fnbA) by novobiocin. The two-component ArlRS system was previously found to decrease the level of supercoiling in S. aureus. Thus, downregulation of arlRS might partially compensate for the relaxing effect of novobiocin. Global analysis and gene mapping of supercoiling-sensitive genes did not provide any indication that they are clustered in the genome. Promoter fusion assays confirmed that the responsiveness of a given gene is intrinsic to the promoter region but independent of the chromosomal location.ConclusionsThe results indicate that the molecular properties of a given promoter, rather than the chromosomal topology, dictate the responsiveness to changes in supercoiling in the pathogen Staphylococcus aureus.
Highlights
It has been shown previously that aminocoumarin antibiotics such as novobiocin lead to immediate downregulation of recA expression and thereby inhibit the SOS response, mutation frequency and recombination capacity in Staphylococcus aureus
We showed that aminocoumarins inhibited the ciprofloxacin-mediated SOS response
The effects of aminocoumarins on recA gene expression are due to GyrB inhibition We previously showed that different aminocoumarins cause severe inhibition of recA transcription [20]
Summary
It has been shown previously that aminocoumarin antibiotics such as novobiocin lead to immediate downregulation of recA expression and thereby inhibit the SOS response, mutation frequency and recombination capacity in Staphylococcus aureus. Aminocoumarins function by inhibiting the ATPase activity of DNA gyrase subunit B with a severe impact on DNA supercoiling. Bacterial chromosomes are usually composed of circular, double-stranded DNA in an overall negatively supercoiled state. Various conditions such as osmotic stress, oxygen tension, temperature changes, the growth phase and certain antibiotics (e.g., aminocoumarins) can change the level of supercoiling, which in turn affects transcription, DNA replication and chromosomal segregation (for reviews, see [1,2,3,4,5,6]). Three enzymes are important for maintaining a steady-state level of supercoiling: topoisomerase I, gyrase and topoisomerase IV.
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