The Kinematics of Explosively Jerky Diatom Motility: A Natural Example of Active Nanofluidics

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Diatom Gliding Motility


Motile diatoms move in the low Reynolds number regime without any apparent organelle for motility. While several possible hypotheses have been proposed, the diatom motility mechanism is not fully understood. In this study, the kinematics of the jerky motion of individual diatoms was investigated at 1.2 millisecond temporal and 9 nm subpixel spatial resolution of species: Nitzschia palea, Navicula cryptocephala, Navicula sp. Centroids of the diatoms were measured from 821 fps digital movies using algorithms for particle tracking. The examination of the displacement data indicated that: 1) for all the diatoms investigated, speed along its trajectory varied from one frame to the next; 2) the motion was not unidirectional; 3) the displacement data included rare large velocities that were as large as 250 εm/s for the Navicula diatoms. The calculated spontaneous accelerations are on the order of 5 × 10 5 εm/s 2. Rapid changes in the orientation angle as large as 2.66 rad/s were observed for Nitzschia palea. The jerky diatom motion could be related to elastic snapping and recoil at the yield point and/or explosive discharge of the mucilage secreted and left on the glass substrate as the “diatom trail.” The flow of mucilage in the slits in the diatom silica valve, called raphes, could be a first example of “active nanofluidics, " which we define as self-propulsion of a fluid. Active nanofluidics could be useful in designing micro- and nanorobots that require pumps for fluid flow.


Biological and Environmental Sciences

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