Fig. 1.

Control of stator unit numbers. (A) Average numbers of H⁺ or Na⁺ stator units in cells expressing only one stator type, in 85 mM Na⁺, showing saturation at inducer concentrations of ∼30 μM arabinose and ∼20 μM IPTG, respectively. Symbols and error bars show the mean and SD of 17–50 motors for each point. (B) Typical example of Na⁺ resurrection at 12 μM IPTG. Speed vs. time of a 1-µm polystyrene bead attached to a flagellar motor (Inset), tracked using back-focal-plane interferometry. Shading indicates the presence of Na⁺ at either 1 mM or 85 mM. Na⁺ was added and removed by flow (hatched regions). Red arrowheads indicate stepwise speed increments following Na⁺ addition.