title: Direct measurement of the flow field around swimming microorganisms.
abstract: Swimming microorganisms create flows that influence their mutual interactions and modify the rheology of their suspensions. While extensively studied theoretically, these flows have not been measured in detail around any freely-swimming microorganism. We report such measurements for the microphytes Volvox carteri and Chlamydomonas reinhardtii. The minute (∼0.3%) density excess of V. carteri over water leads to a strongly dominant Stokeslet contribution, with the widely-assumed stresslet flow only a correction to the subleading source dipole term. This implies that suspensions of V. carteri have features similar to suspensions of sedimenting particles. The flow in the region around C. reinhardtii where significant hydrodynamic interaction is likely to occur differs qualitatively from a puller stresslet, and can be described by a simple three-Stokeslet model.
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, United Kingdom.
authors.forename: Knut
authors.initials: K
authors.lastname: Drescher
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Goldstein
authors.forename: Nicolas
authors.initials: N
authors.lastname: Michel
authors.forename: Marco
authors.initials: M
authors.lastname: Polin
authors.forename: Idan
authors.initials: I
authors.lastname: Tuval
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000502:physiology*; D009068:Movement / Q000502:physiology; D012212:Rheology / Q000379:methods*; D013997:Time Factors; D044446:Volvox / Q000502:physiology*