Regulation of Hydrogen Peroxide-Dependent Gene Expression in Rhodobacter sphaeroides : Regulatory Functions of OxyR

Genome-wide transcriptome profiling was used to reveal hydrogen peroxide (H 2 O 2 )-dependent regulatory mechanisms in the facultatively photosynthetic bacterium Rhodobacter sphaeroides . In this study we focused on the role of the OxyR protein, a known regulator of the H 2 O 2 response in bacteria. The transcriptome profiles of R. sphaeroides wild-type and oxyR mutant strains that were exposed to 1 mM H 2 O 2 for 7 min or were not exposed to H 2 O 2 were analyzed. Three classes of OxyR-dependent genes were identified based on their expression patterns in the wild type of oxyR mutant strains with differing predicted roles of oxidized and reduced OxyR as activators of transcription. DNA binding studies revealed that OxyR binds upstream of class I genes, which are induced by H 2 O 2 and exhibit similar basal levels of expression in the wild-type and oxyR mutant strains. The effect of OxyR on class II genes, which are also induced by H 2 O 2 but exhibit significantly lower basal levels of expression in the wild-type strain than in the mutant, is indirect. Interestingly, reduced OxyR also activates expression of few genes (class III). The role of reduced OxyR as an activator is shown for the first time. Our data reveal that the OxyR-mediated response is fast and transient. In addition, we found that additional regulatory pathways are involved in the H 2 O 2 response.