Reverse Engineering the Euglenoid Movement
Euglenids exhibit an unconventional motility strategy amongst unicellular eukaryotes, consisting of large amplitude highly concerted deformations of the entire body (euglenoid movement or metaboly). A plastic cell envelope called pellicle mediates these deformations. Unlike ciliary or flagellar motility, the biophysics of this mode is not well understood. We examine quantitatively video recordings of four euglenids executing such motions with statistical learning methods, revealing strokes of high uniformity. We then interpret the observations with a theory for the pellicle kinematics, providing a precise understanding of the link between local actuation by pellicle shear and shape control. We find that two of our euglenids execute their stroke at constant body volume, the other two exhibit deviations of about 20% from their average volume, challenging current models of low Reynolds number locomotion.The active pellicle shear deformations can reach 340%. Moreover, we find that metaboly accomplishes locomotion at hydrodynamic efficiencies comparable to those of ciliates and flagellates. Our results suggest new quantitative experiments, provide insight into the evolutionary history of euglenids, and suggest that the pellicle may serve as a model for engineered active surfaces with applications in micro-fluidics.Arroyo, Heltai, Millan and DeSimone, PNAS (in press).View Large Image | View Hi-Res Image | Download PowerPoint Slide