Defense arsenal of the strict anaerobe Clostridioides difficile against reactive oxygen species encountered during its infection cycle

Abstract

Clostridioides difficile, a strict anaerobe, is the major cause of antibiotic-associated diarrhea. This enteropathogen must adapt to oxidative stress mediated by reactive oxygen species (ROS), notably those released by the neutrophils and macrophages recruited to the site of infection or those endogenously produced upon high oxygen (O2) exposure. C. difficile uses a superoxide reductase, Sor, and several peroxidases to detoxify ROS. We showed that Sor has a superoxide reductase activity in vitro and protects the bacterium from exposure to menadione, a superoxide donor. After confirming the peroxidase activity of the rubrerythrin, Rbr, we showed that this enzyme together with the peroxiredoxin, Bcp, plays a central role in the detoxification of H2O2 and promotes the survival of C. difficile in the presence of not only H2O2 but also air or 4% O2. Under high O2 concentrations encountered in the gastrointestinal tract, the bacterium generated endogenous H2O2. The two O2 reductases, RevRbr2 and FdpF, have also a peroxidase activity and participate in H2O2 resistance. The CD0828 gene, which also contributes to H2O2 protection, forms an operon with rbr, sor, and perR encoding a H2O2-sensing repressor. The expression of the genes encoding the ROS reductases and the CD0828 protein was induced upon exposure to either H2O2 or air. We showed that the induction of the rbr operon is mediated not only by PerR but also by OseR, a recently identified O2-responsive regulator of C.