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Chlamydomonas Swims with Two “Gears” in a Eukaryotic Version of Run-and-Tumble Locomotion

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Science  24 Jul 2009:
Vol. 325, Issue 5939, pp. 487-490
DOI: 10.1126/science.1172667

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All Together Now (Sometimes)

Motile cilia and flagella protrude from the surface of many eukaryotic cells. Understanding how cilia and flagella operate is important for understanding ciliated cells in metazoans, the ecology and behavior of motile microorganisms, and the mechanisms of molecular motors and signal transduction. Using very-high-speed video microscopy, Polin et al. (p. 487; see the Perspective by Stocker and Durham) discovered that the biflagellated cells of the single-cell alga Chlamydomonas rheinhartii switch between synchronous beating, which keeps the cells traveling forward, and asynchronous beating, which allows the organisms to make sharp turns. This random progression occurs in the dark and allows cells to diffuse, and it may underpin directional movement toward light in the same way that the run-and-tumble behavior of prokaryotes allows them to move up chemical gradients.

Abstract

The coordination of eukaryotic flagella is essential for many of the most basic processes of life (motility, sensing, and development), yet its emergence and regulation and its connection to locomotion are poorly understood. Previous studies show that the unicellular alga Chlamydomonas, widely regarded as an ideal system in which to study flagellar biology, swims forward by the synchronous action of its two flagella. Using high-speed imaging over long intervals, we found a richer behavior: A cell swimming in the dark stochastically switches between synchronous and asynchronous flagellar beating. Three-dimensional tracking shows that these regimes lead, respectively, to nearly straight swimming and to abrupt large reorientations, which yield a eukaryotic version of the "run-and-tumble" motion of peritrichously flagellated bacteria.

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