Regulation of perR expression by iron and PerR in Campylobacter jejuni

Campylobacter jejuni is a leading foodborne pathogen causing gastroenteritis in humans. Although OxyR is a widespread oxidative stress regulator in many Gram-negative bacteria, C. jejuni lacks OxyR and instead possesses the metalloregulator PerR. Despite the important role played by PerR in oxidative stress defense, little is known about the factors influencing perR expression in C. jejuni. In this study, the perR promoter-lacZ fusion assay demonstrated that iron significantly reduced the level of perR transcription, whereas other metal ions, such as copper, cobalt, manganese and zinc, did not affect perR transcription. Notably, a perR mutation substantially increased the level of perR transcription and in trans complementation restored the transcriptional changes, suggesting perR is transcriptionally autoregulated in C. jejuni. In the perR mutant, iron did not repress perR transcription, indicating the iron-dependence of perR expression results from perR autoregulation. Electrophoretic mobility shift assays showed that PerR binds to the perR promoter, and DNase I footprinting assays identified a PerR binding site overlapping the -35 region of the two perR promoters, further supporting perR autoregulation at the transcriptional level. Alignment of the PerR binding sequence in the perR promoter with the regulatory region of other PerR regulon genes of C. jejuni revealed a 16-bp consensus PerR binding sequence, which shares high similarities to the B. subtilis PerR box. The results of this study demonstrated that PerR directly interacts with the perR promoter and regulates perR transcription, and that perR autoregulation is responsible for the repression of perR transcription by iron in C. jejuni.