01778nas a2200157   4500008004100000245009800041210006900139300001400208490000700222520126400229100002201493700001801515700001901533700002201552856004601574       2019                        eng d00aSwimming Euglena respond to confinement with a behavioural change enabling effective crawling0 aSwimming Euglena respond to confinement with a behavioural chang  a496–5020 v153 aSome euglenids, a family of aquatic unicellular organisms, can develop highly concerted, large-amplitude peristaltic body deformations. This remarkable behaviour has been known for centuries. Yet, its function remains controversial, and is even viewed as a functionless ancestral vestige. Here, by examining swimming Euglena gracilis in environments of controlled crowding and geometry, we show that this behaviour is triggered by confinement. Under these conditions, it allows cells to switch from unviable flagellar swimming to a new and highly robust mode of fast crawling, which can deal with extreme geometric confinement and turn both frictional and hydraulic resistance into propulsive forces. To understand how a single cell can control such an adaptable and robust mode of locomotion, we developed a computational model of the motile apparatus of Euglena cells consisting of an active striated cell envelope. Our modelling shows that gait adaptability does not require specific mechanosensitive feedback but instead can be explained by the mechanical self-regulation of an elastic and extended motor system. Our study thus identifies a locomotory function and the operating principles of the adaptable peristaltic body deformation of Euglena cells.1 aNoselli, Giovanni1 aBeran, Alfred1 aArroyo, Marino1 aDeSimone, Antonio  uhttps://doi.org/10.1038/s41567-019-0425-802261nas a2200169   4500008004100000245010000041210006900141300001600210490000800226520169900234100002401933700002601957700001801983700002202001700002202023856004602045       2017                        eng d00aKinematics of flagellar swimming in Euglena gracilis: Helical trajectories and flagellar shapes0 aKinematics of flagellar swimming in Euglena gracilis Helical tra  a13085-130900 v1143 aActive flagella provide the propulsion mechanism for a large variety of swimming eukaryotic microorganisms, from protists to sperm cells. Planar and helical beating patterns of these structures are recurrent and widely studied. The fast spinning motion of the locomotory flagellum of the alga Euglena gracilis constitutes a remarkable exception to these patterns. We report a quantitative description of the 3D flagellar beating in swimming E. gracilis. Given their complexity, these shapes cannot be directly imaged with current microscopy techniques. We show how to overcome these limitations by developing a method to reconstruct in full the 3D kinematics of the cell from conventional 2D microscopy images, based on the exact characterization of the helical motion of the cell body.The flagellar swimming of euglenids, which are propelled by a single anterior flagellum, is characterized by a generalized helical motion. The 3D nature of this swimming motion, which lacks some of the symmetries enjoyed by more common model systems, and the complex flagellar beating shapes that power it make its quantitative description challenging. In this work, we provide a quantitative, 3D, highly resolved reconstruction of the swimming trajectories and flagellar shapes of specimens of Euglena gracilis. We achieved this task by using high-speed 2D image recordings taken with a conventional inverted microscope combined with a precise characterization of the helical motion of the cell body to lift the 2D data to 3D trajectories. The propulsion mechanism is discussed. Our results constitute a basis for future biophysical research on a relatively unexplored type of eukaryotic flagellar movement.1 aRossi, Massimiliano1 aCicconofri, Giancarlo1 aBeran, Alfred1 aNoselli, Giovanni1 aDeSimone, Antonio  uhttps://www.pnas.org/content/114/50/13085