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Reactive oxygen species-based sensing by a single chemoreceptor controls bacterial chemotaxis to copper

Cell motility is a widespread strategy to maintain the fitness of unicellular and multicellular living organisms. This cellular process relies on a chemoreceptor-dependent sensing of the environment which is converted into an intracellular signal modulating flagellum or cilium rotation. Yet the detailed molecular mechanisms operating at the chemoreceptor sensor domain remain largely unclear. Here we propose that the negative chemotactic response to toxic copper (Cu) in the free-living bacterium Caulobacter crescentus implies an original two-step sensing process based on a Cu binding to the sensor domain of the newly identified chemoreceptor McpR and on the generation of reactive oxygen species (ROS) by Cu. We also provide evidence that the McpR-bound Cu undergoes a redox cycling modulating McpR conformation, which thereby allows a fine and rapid redox tuning of the chemoreceptor activity and the underlying chemotactic response.