FIG. 1.

Change in swimming speed of normal-light-grown R. sphaeroides cells in response to a flash of light of a different wavelength and duration. (A and C) Average behavior of 10 cells in response to a 1-s flash of white (A) or blue (C) light. (B and D) Change in mean speed of the population of at least 100 free-swimming cells in response to a 30-s pulse of white (B) or blue (D) light. (E and F) Behavior of two individual cells at the end of a flash of blue light. ▴, light on; ▾, light off. The apparent slow swimming speed on the step down in light is the result of the distribution of response times shown by cells in the population (E and F).