Escherichia coli's physiology can turn membrane voltage dyes into actuators

Bacteria tend to maintain an energy-costly electric potential across the biological membrane. The voltage thus stored can then be reinvested to fuel essential reactions, such as those required for feeding, movement and anabolism. Assays of Nernstian membrane voltage dyes accumulation are arguably the most widespread techniques to quantify such potential. However, interactions of such molecules with the complex cellular environment and physiology are often poorly understood. Here, we characterize the parametrical landscape in which these molecules behave like sensors and where they actually take the role of actuators. We recommend an experimental framework that can be used to characterize Nernstian dyes and we apply it to the characterization of the dye Thioflavin T in E. coli.