Indole modulates cooperative protein-protein interactions in the flagellar motor.

Indole is a major component of the bacterial exometabolome, and the mechanisms for its wide-ranging effects on bacterial physiology are biomedically significant, although they remain poorly understood. Here, we determined how indole modulates the functions of a widely conserved motility apparatus, the bacterial flagellum. Our experiments in Escherichia coli revealed that indole influences the rotation rates and reversals in the flagellum's direction of rotation via multiple mechanisms. At concentrations higher than 1 mM, indole decreased the membrane potential to dissipate the power available for the rotation of the motor that operates the flagellum. Below 1 mM, indole did not dissipate the membrane potential. Instead, experiments and modeling indicated that indole weakens cooperative protein interactions within the flagellar complexes to inhibit motility. The metabolite also induced reversals in the rotational direction of the motor to promote a weak chemotactic response, even when the chemotaxis response regulator, CheY, was lacking. Experiments further revealed that indole does not require the transporter Mtr to cross the membrane and influence motor functions. Based on these findings, we propose that indole modulates intra- and inter-protein interactions in the cell to influence several physiological functions.

Unappreciated Roles for K+ Channels in Bacterial Physiology.

Potassium (K+) channels are highly conserved proteins found in all domains of life, that allow for selective movement of K+ ions across membranes. Despite their broad distribution, the physiological roles of individual members of this diverse channel family have only been thoroughly explored in eukaryotic systems, where they have critical functions in a variety of cellular processes. Recent studies have demonstrated that bacterial K+ channels have integral roles in electrical signaling, information propagation, and intercellular communication. We discuss how these novel findings impact our understanding of bacterial physiology and the need to continue to explore the native roles of ion channels in microbes.