Abstract

Eukaryotic microswimmer Trypanosoma Brucei is a unicellular eukaryotic parasite that causes sleeping sickness in cattle and humans, impairing the economy and public health of sub-Sahara Africa. During its life cycle, Trypanosoma navigates through complex and distinct environments, ranging from the narrow gut of tsetse flies to the crowded blood vessels of mammals. Due to its rapid motion and complex body deformation, conventional optical microscopy failed to provide enough information to fully reveal the dynamics in 3D, leaving the exact swimming mechanism in debate.

In this talk, I will show our recent experimental and simulation results which unveil surprising features of their swimming behavior. By tracking the three-dimensional trajectories of fluorescent particles attached to the cell surface, we find that T. brucei propagates a rapid right-handed helical wave along the flagellum to generate thrust like a corkscrew. The cell body, laterally attached along the flagellum, counter-rotates at a lower frequency due to reactive torque, and traces out a left-handed helical path as the cell swims forward. The observed flower-like tracer trajectories result from the superposition of these coupled motions under torque-free constraints. Simulations using the regularized Stokeslets method reproduce the observed dynamics and reveal an optimal body bending angle that enhances forward motion with reduced rotation. These findings uncover a distinct mode of eukaryotic flagellar motility and rebuild the foundation for understanding T. brucei navigation in vivo and inspire new designs of biomimicking actuators.

The work has recently been published in PNAS: www.pnas.org/doi/10.1073/pnas.2536746123