Trypanosoma swims with a unidirectionally rotating body and a bidirectionally rotating flagellum*

The motility of Trypanosoma Brucei (TB), a parasite causing sleeping sickness in mammals, is difficult to quantify, since its rapid and complex body motion challenges conventional microscopy techniques. In this study, by tracking the 3D motion of fluorescent particles attached to their body using out-of-focus diffraction patterns, we are able to obtain high-frame-rate data on the TB deformation dynamics. Our results indicate that TB exhibits a unique locomotion pattern consisting of three distinct components: unidirectional rotation, oscillatory rotation, and flagellar bending. The combined azimuth oscillation and bending propagate a kink wave along the flagella, which drives TB forward. The unidirectional rotation of the TB body is due to its chiral body-shape undergoing a translation. The amplitudes of both the azimuthal oscillation and bending decrease from the anterior to the posterior end, due to the conservation of linear and angular momentum. Numerical simulations produce quantitatively agreeing results. Understanding the biomechanics of TB swimming will allow us to further decipher their unique self-propulsion mechanism in complex environments and flow conditions.