Fig. 1.

Light-powering of PR⁺ E. coli. (a) Overview of spectra and spectral overlaps. The PR absorption spectrum [redrawn from Beja (4)] is shown in black, with green and red bars indicating illumination wavelengths. (b) Single PR⁺ bacterium swims faster when illuminated with green light. The cell's position is recorded at a rate of 0.5 Hz via constant red dark-field illumination throughout the entire track. Illumination with green light at the absorption peak is periodic (20 s on, 20 s off) and occurs only during green circles of the path. Velocity during periods of green illumination (10.6 ± 0.9 μm/s) is 96% higher than during periods of red illumination alone (5.4 ± 0.4 μm/s; P < 0.005, one-tailed t test). Respiration has been inhibited with 30 mM azide in motility buffer. (Inset) Raw tiled movie frames of swimming cell.