title: Centripetal focusing of gyrotactic phytoplankton.
abstract: A suspension of gyrotactic microalgae Chlamydomonas augustae swimming in a cylindrical water vessel in solid-body rotation is studied. Our experiments show that swimming algae form an aggregate around the axis of rotation, whose intensity increases with the rotation speed. We explain this phenomenon by the centripetal orientation of the swimming direction towards the axis of rotation. This centripetal focusing is contrasted by diffusive fluxes due to stochastic reorientation of the cells. The competition of the two effects lead to a stationary distribution, which we analytically derive from a refined mathematical model of gyrotactic swimmers. The temporal evolution of the cell distribution, obtained via numerical simulations of the stochastic model, is in quantitative agreement with the experimental measurements in the range of parameters explored.
authors.affiliation: Institute of Complex Systems-CNR, via dei Taurini 19, 00185 Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Cencini
authors.affiliation: Department of Life Sciences and Systems Biology, University of Torino, via Accademia Albertina 13, 10123 Torino, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Franchino
authors.affiliation: Department of Physics and INFN, University of Torino, via P.Giuria 1, 10125 Torino, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Santamaria
authors.affiliation: Department of Physics and INFN, University of Torino, via P.Giuria 1, 10125 Torino, Italy. Electronic address: guido.boffetta@unito.it.
authors.forename: G
authors.initials: G
authors.lastname: Boffetta
mesh_terms: D001696:Biomechanical Phenomena; D002696:Chlamydomonas / Q000502:physiology; D003198:Computer Simulation; D010839:Phytoplankton / Q000502:physiology*; D012399:Rotation; D013997:Time Factors
keywords: Fluid-flow motility interaction; Gyrotaxis; Microorganism motility