Fig. 2.

Bacterial trajectories. Tracking trajectories (red lines) for S. oneidensis MR-1 cells during 10-sec video samples captured using 100× magnification. In all four experiments the bacteria are using 20 mM lactate as their carbon source. The strains were captured on video while sealed in anaerobic capillary tubes. (A) An Fe(OH)₃ particle (located in the center of the frame) elicited considerably less motility response than an MnO₂ particle (located left center) (B) where cells were observed swimming at speeds of 40–80 μm/sec. Touch-and-go behavior, in which the bacteria briefly contact the metal oxide surface, was observed for the next 2 h (Movie S1). (C) Trajectory diagram for 10 sec of video at 100× magnification adjacent to the working electrode. Video captured after MR-1 was exposed to 10 min at 0 mV vs. graphite reference electrode. (D) Video captured after MR-1 was exposed to 10 min at +600 mV. Swimming increased immediately (1−30 sec) after the voltage was applied, then continued to increase over the next 20 min. At 0 mV or any relatively lower voltage the motility activity decreased but returned when +600 mV was reapplied (Movie S6). Approximate boundaries of the mineral particles and the location of the graphite electrodes are shown by dashed white lines.