Anaerobic bacteria use the ancient Rubredoxin / Rubredoxin Reductase (Rdx/RdxR) system for the detoxification of oxygen and the inactivation of reactive oxygen species (ROS). In Pseudomonas aeruginosa this system is only known to be necessary for growth on alkanes. We identified the Rdx/RdxR system in a highly virulent CF- isolate as being essential for survival and proliferation after phagocytosis by human polymorphonuclear leucocytes. Transcriptome analyses showed that the Rdx/RdxR system is upregulated in several highly virulent CF isolates under high oxidative stress and in the stationary growth phase. An rdxR mutant was severely impaired in quorum sensing and exhibited lower virulence in animal infection models. The bacterial cells had in vitro a substantially reduced resistance to ROS and had to face a higher oxidative stress (e.g. higher levels of cis-methylene fatty acids and increased Fe(III)/Fe(II) ratio). By complementation in trans these changes could be reverted in vivo and also in vitro by adding the heterologously expressed Rdx system to a RdxR knock out mutant cell lysate. We showed that the Rdx/RdxR system transfers electrons with very high efficiency and nearly diffusion controlled to oxidized iron centres, keeping them in the reduced, reactive state. This enables P. aeruginosa to keep these proteins in an active state during oxygen stress and moreover to gain energy from the degradation of ROS. These findings support the hypothesis that the ancient oxygen protecting Rdx/RdxR system can act in P. aeruginosa as a highly efficient mechanism to minimize oxidative stress and facilitates persistence and proliferation in infected hosts.
Wiehlmann et al. (Mon,) studied this question.