Enterohemorrhagic Escherichia coli senses colonic oxygen availability to modulate its virulence and colonization.

Intestinal oxygen gradients influence both gut homeostasis and pathogen colonization. Although oxygen release can promote infections like those caused by Citrobacter rodentium, it was unknown whether oxygen directly controls bacterial virulence systems. In this study, we demonstrate that enterohemorrhagic Escherichia coli (EHEC) senses oxygen via the metabolic two-component system ArcAB to regulate its type 3 secretion system (T3SS). Under low oxygen, phosphorylated ArcA binds the promoter of ler, which encodes the T3SS master regulator, to repress its expression. When oxygen increases, ArcB kinase activity is inhibited, leading to ArcA dephosphorylation and T3SS derepression. This oxygen-responsive ArcAB pathway is absent in C. rodentium, reflecting evolutionary adaptation. Additionally, ArcA suppresses Shiga toxin production. Our work reveals the ArcAB two-component system as a pivotal oxygen-sensing pathway that directly orchestrates locus of enterocyte effacement (LEE) gene expression and positions it as a promising target for antivirulence or metabolic interference strategies.