Fig. 3.

Hybrid fuel motors. (A) Speed vs. time of a hybrid motor with low expression level of both stator components (8 µM arabinose and 10 µM IPTG). Color marking is same as in Fig. 1B. Speed histograms with multiple-Gaussian fits (Right) quantify the speed increments following the addition of 1 mM (gray) and 85 mM (black) Na⁺. (B) Speed vs. time of a hybrid motor as in A, but with greater expression of stator proteins (10 µM arabinose and 25 µM IPTG). Black line shows data Chung–Kennedy-filtered with a 1-s window; blue arrowheads indicate stepwise speed increments corresponding to H⁺ resurrection. (C) Speed increment distributions for 0 mM, 1 mM, and 85 mM Na⁺, for a total of 56, 56, and 79 increments (21, 14, and 17 separate motors), respectively. (Inset) Speed increment (ordinate, hertz) vs. external Na⁺ concentration (abscissa, millimolar), compared with previous results with PomA/PotB motors (26), red line). The size of speed increments did not depend upon expression levels. (D) Schematic of the transition between a proton motor and a hybrid fuel motor upon the addition of Na⁺.