Figure 1
Single cell phototaxis of C. reinhardtii. (a) Sample trajectories, starting at the star-marked points. Cells approach the centre of the light field, circulate around it at an average distance ρ c marked by the red dashed circle, and then leave the field of view. (b) Experimental histograms of cells’ directions at ρ = 78 μm (green), 156 μm (blue), and 780 μm (red). The angle is oriented radially outwards. (c) Representative trajectories from local gradient model, with α = α max, starting at ρ = ρ c with initial orientations θ = 205° (blue) and 162° (green). For clarity, only half of each trajectory is displayed. Red dashed circle has radius ρ c . The underlying light field is the best Gaussian fit to the experimental one. (d) Ratio between the average light intensity seen by a swimmer circulating at ρ = ρ c and moving along trochoidal trajectories starting at (ρ c , θ 0) (blue circles; dotted line: guide to the eye). Black dashed line: average value of the relative increase in irradiance (29%).
