A newly identified detoxification system protects uropathogenic Escherichia coli from reactive chlorine species

Neutrophils eliminate invading pathogens through the production of reactive oxygen and chlorine species (ROS/RCS), with hypochlorous acid (HOCl) representing the most abundant and bactericidal oxidant produced in this process. Compared to bacterial defenses against ROS, which are well studied, little is known about how pathogens respond to and counter RCS, including HOCl. Here, we identify and mechanistically characterize RcrB, a protein of the uncharacterized DUF417 protein family, for which no role in oxidative stress defense has been described yet. We report a previously unrecognized role as an RCS detoxification system that confers high-level resistance to uropathogenic Escherichia coli (UPEC). We show that RcrB is an inner membrane protein and strongly induced during RCS exposure and phagocytosis. Loss of RcrB results in profound HOCl hypersensitivity, accompanied by elevated macromolecular damage and severe metabolic perturbations, establishing RcrB as a central determinant of UPECs RCS stress resistance. Heterologous expression of RcrB in HOCl-sensitive intestinal E. coli strains is sufficient to restore resistance but requires functional glutathione biosynthesis. Quantitative HOCl trapping assays demonstrate that RcrB expression protects the bacterial population by significantly reducing extracellular HOCl, indicating active chemical quenching rather than passive membrane protection. Structure-function analysis of RcrB confirms this conclusion and demonstrate that conserved, redox-active amino acids facing the periplasm are essential for its detoxification activity. In summary, our study reveals a hitherto unknown bacterial strategy for mitigating RCS and reveal a distinct mechanism by which UPEC may survive the mammalian host defense. Significance StatementDuring infection, human immune cells such as neutrophils kill bacteria by releasing powerful oxidants, including hypochlorous acid (HOCl), the active ingredient of household bleach. How pathogenic bacteria survive this chemical attack is still poorly understood. This study identifies a membrane protein in uropathogenic Escherichia coli as a key defense factor that neutralizes HOCl before it can damage the cell. RcrB acts at the bacterial cell envelope, where it detoxifies HOCl in a glutathione-dependent manner to maintain a balanced redox homeostasis and cellular integrity, thereby even protect neighboring bacteria. These findings reveal a previously unrecognized frontline defense strategy that helps pathogens survive immune attack and may represent a new target for antimicrobial therapies.