Fig. 2. (A) Definition of laboratory axes x, y and body-fixed axes X, Y. (B) Wiggling movement of the basal body on a helical trajectory as it swims with its two flagella in the vicinity of a substrate. (C) Displacements of basal body xBB and yBB relative to the original position at t = 0 showing small-scale oscillations with a frequency of 21.28 Hz (beating frequency of flagella) embedded in large-scale oscillations of frequency around 0.63 Hz. The dashed lines in magenta highlight the first 800 frames that are used for tracking in Fig. 1. (D) Power spectrum of xBB and yBB displays clear peaks at two frequencies of 21.28 and 0.63 Hz (see Video S2, ESI†).
