Aer is a bidirectional redox sensor mediating negative chemotaxis to antibiotic-induced ROS in E. coli

The Aer chemoreceptor in E. coli is known to perform oxygen- or aero-taxis by sensing metabolic flux through ETC via an FAD cofactor bound to its PAS domain. We show in this study that Aer also senses oxidative stress and performs FAD-dependent negative chemotaxis in response to the known ROS H 2 O 2 . The ability of Aer to detect both oxidizing and reducing intracellular environments redefines its functional range and establishes Aer as a bidirectional redox sensor. We show in addition that the ability of bacterial swarms to move away from bactericidal antibiotics is Aer-dependent and is abolished by expression of the catalase–peroxidase enzyme KatG, which scavenges intracellular ROS. Our study thus provides independent behavioral evidence that certain antibiotics generate intracellular ROS, while also offering a sensitive assay for detecting these reactive species. Importance Motile bacteria rely on aerotaxis to seek environments that maximize energy production. We show that in E. coli , Aer mediates not only positive chemotaxis toward favorable redox conditions but also negative chemotaxis in response to oxidative stress. The ability of Aer to detect both oxidizing and reducing cellular environments reveals an unexpected sensory versatility, shared to varying degrees by other E. coli chemoreceptors. We show that E. coli uses Aer to actively move away from ROS-generating antibiotics, revealing a previously unrecognized behavioral mechanism for bacterial survival under oxidative stress.