Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session S29: Swimming with Flagella |
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Chair: Kenny Breuer, Brown University Room: Ballroom III |
Tuesday, November 22, 2011 3:05PM - 3:18PM |
S29.00001: Particle image velocimetry experiments on a model helical flagellum in viscoelastic fluids Anand Desai, Bin Liu, Thomas Powers, Kenneth Breuer Live bacteria often live in polymer suspensions, and are inevitably subjected to the effects of fluid viscoelasticity. To study the viscoelastic effect on bacterial motility, we have constructed a scaled-up model system and use particle image velocimetry (PIV) to measure the flow field generated by a rigid helical filament that rotates and translates in a Boger fluid. The helix is made to swim freely -- it is subjected to an external torque, and translates along its axial direction at a predetermined speed so that the net hydrodynamic force on the helix vanishes. By comparing the flow field with the Newtonian reference, we address the question on how the viscoelasticity of the fluid enhances or reduces the motility of the helix at different Deborah numbers. [Preview Abstract] |
Tuesday, November 22, 2011 3:18PM - 3:31PM |
S29.00002: Force-free swimming of a model helical flagellum in viscoelastic fluids Bin Liu, Thomas Powers, Kenneth Breuer Many bacteria swim by rotating helical flagella. These cells often live in polymer suspensions, which are viscoelastic. Recently there have been several theoretical and experimental studies showing that viscoelasticity can either enhance or suppress propulsion, depending on the details of the microswimmer. To help clarify this situation, we study experimentally the motility of the flagellum using a scaled-up model system - a motorized helical coil that rotates along its axial direction. The rotating helix is tethered on a linear stage that advances at prescribed speeds along the axial direction. A free-swimming speed is obtained when the net force on the helix is zero. In the Newtonian case, the free-swimming speed of the helix matches the predictions from the slender body theory and the boundary element method, with increasing order of agreement as the numerical strategy improves. When the helix is immersed in a viscoelastic (Boger) fluid, we find an increase in the force-free swimming speed. The enhancement is maximized at a Deborah number of approximately one, and the magnitude depends not only on the elasticity of the fluid but also on the geometry of the helix. [Preview Abstract] |
Tuesday, November 22, 2011 3:31PM - 3:44PM |
S29.00003: Flagellar generated flow mediates attachment of \textit{Giardia Lamblia} Theodore Picou, Jamie Polackwich, Beatriz Burrola Gabilondo, Ryan McAllister, Tom Powers, Heidi Elmendorf, Jeff Urbach \textit{Giardia lamblia} is a protozoan parasite responsible for widespread diarrheal disease in humans and animals worldwide. Attachment to the host intestinal mucosa and resistance to peristalsis is necessary for establishing infection, but the physical basis for this attachment is poorly understood. We report results from confocal fluorescence microscopy that demonstrate that the regular beating of the posterior flagella generate a flow through the ventral disk, a suction-cup shaped structure that is against the substrate during attachment. Finite element simulations show that the negative pressure generated by the flow is consistent with the measured force of attachement between the parasite and its substrate. [Preview Abstract] |
Tuesday, November 22, 2011 3:44PM - 3:57PM |
S29.00004: Hydrodynamic effects on the tumbling of flagellated bacteria near a solid surface Mehdi Molaei, Jian Sheng Peritrichously flagellated bacteria use semi-rigid helical flagella to form a bundle during a run to swim forward and to trigger the unbundling during a tumble to change their swimming direction. It is accepted that the hydrodynamic interactions play a significant role in these processes. Recently, using digital holographic microscopy and microfluidics, we discovered that the tumbling events are substantially suppressed near a solid wall. In this paper, we present a two flagellum rigid model to elucidate the hydrodynamic wall interaction mechanism behind the phenomenon. Further implications on cell attachment and detachment during the biofilm formation will be discussed. We apply Slender Body Theory (SBT) to quantify the flow flagellum interaction. The no-slip boundary imposed by the wall is modeled using the image system of the SBT model for the stoke-flow singularity. We show that in the bulk, a repulsive force among flagella initiates the unbundling and consequently tumbling; however, in presence of the wall, the force is strongly mitigated that stabilize the bundle and suppress the tumbling. [Preview Abstract] |
Tuesday, November 22, 2011 3:57PM - 4:10PM |
S29.00005: Hydrodynamic Interactions of Hyperactivated Sperm Sarah Olson, Lisa Fauci Hyperactivated sperm motility is correlated to an increase in calcium concentration within the flagellum and is characterized by highly asymmetrical waveforms and circular trajectories. Previous computational studies of flagellum with symmetrical waveforms have shown that multiple sperm swimming with waveforms that are out of phase will eventually phase lock due to hydrodynamic interactions. The focus of this research is to study the hydrodynamic interactions of hyperactivated sperm swimming in proximity in both an unbounded fluid domain and near a wall. [Preview Abstract] |
Tuesday, November 22, 2011 4:10PM - 4:23PM |
S29.00006: Locomotive consequences of non-axisymmetric flagellar configurations Henry Fu, Marcos Marcos, YunKyong Hyon, Thomas Powers, Roman Stocker Although peritrichous bacteria can form flagellar bundles at many attachment points and directions relative to the cell body, locomotion of these bacteria is often modeled as arising from a polar bundle oriented along the cell body axis. We discuss the consequences of non-axisymmetric flagellar configurations for bacterial locomotion and implications for bacterial behavior using a boundary element method (BEM) based on the method of regularized Stokeslets. We validate our BEM by comparing to analytic results for spheres and ellipsoids, as well as results in the literature for axisymmetric flagella with spherical and ellipsoidal heads obtained from other boundary element methods and slender body theory. Non-axisymmetric flagellar configurations generically lead to wobbling cell bodies and wiggling helical cell trajectories, both of which have been observed experimentally. We compare experimental and numerically calculated wiggling trajectories to deduce information about flagellar geometries of swimming B. subtilis. We discuss the implications of off-axis flagellar geometries for bacterial rheotaxis and chemotaxis. [Preview Abstract] |
Tuesday, November 22, 2011 4:23PM - 4:36PM |
S29.00007: Propulsion of microorganisms by a helical flagellum Bruce Rodenborn, Chih-Hung Chen, Harry L. Swinney, H.P. Zhang Many microorganisms are propelled by rotating helical flagella. We examine this propulsion in laboratory measurements on macroscopic rotating helices (typical diameter, 12 mm) in a fluid with viscosity $10^5$ times that of water; thus the Reynolds number in the experiments is much less than unity, just as for bacteria. We directly measure the propulsive force and torque generated by a rotating flagellum, and the drag force on a translating flagellum, i.e. elements of the propulsion matrices. Our results differ significantly from the predictions of Lighthill's Resistive Force Theory (1975), which treats each segment as an independent slender rod and neglects hydrodynamic interactions between segments of the flagellum. The difference between our measurements and Resistive Force Theory is especially large for helices with small pitch/diameter ratios, which is the regime of many bacteria. We also compute force, torque and drag using the regularized Stokelets method of Cortez et al. (2005). Our numerical results from the regularized Stokelets method are in excellent agreement with the laboratory measurements for helices with parameters (pitch/diameter and length/pitch) in the biologically relevant regime. [Preview Abstract] |
Tuesday, November 22, 2011 4:36PM - 4:49PM |
S29.00008: Flagellar waveform analysis of swimming algal cells Huseyin Kurtuldu, Karl Johnson, Jerry Gollub The twin flagella of the green alga \textit{Chlamydomas reinhardtii} are driven by dynein molecular motors to oscillate at about 50-60 Hz in a breaststroke motion. For decades, \textit{Chlamydomas} has been used as a model organism for studies of flagellar motility, and of genetic disorders of ciliary motion. However, little is known experimentally about the flagellar waveforms, and the resulting time-dependent force distribution along the 250 nm diameter flagella. Here, we study flagellar dynamics experimentally by confining cells in quasi-2D liquid films. From simultaneous measurements of the cell body velocity and the time-dependent velocities along the center lines of the two flagella, we determine the drag coefficients, and estimate the power expended by the body and the flagella, comparing our findings with measurements\footnote{J.S. Guasto et al., Phys. Rev. Lett. 105, 168102 (2010)} based on the induced fluid flow field. We contrast the results for the quite different beating patterns of synchronous and asynchronous flagella, respectively. [Preview Abstract] |
Tuesday, November 22, 2011 4:49PM - 5:02PM |
S29.00009: Marine bacteria exploit Euler buckling to turn Kwangmin Son, Jeffrey S. Guasto, Arnaud Lazarus, James Miller, Pedro M. Reis, Roman Stocker Important species of marine bacteria were recently discovered to swim in a three-step pattern: they swim forward by rotating a single helical flagellum, then backwards by reversing the flagellar rotation, and finally ``flick'' the flagellum in an off-axis motion, producing a large ($\sim90^{\circ}$) reorientation in the swimming direction. What remains unknown in this elegant, minimalistic swimming pattern are the biomechanics of the flick. Here we present new observations based on high-speed video microscopy to capture the detailed dynamics of the reorientation process in \textit{Vibrio alginolyticus}. Combining the data with a model of buckling of thin structures, we show that the onset of forward swimming triggers a mechanical instability of the flagellar hook, because the propulsive force exceeds the threshold for Euler buckling. This surprising adaptation, where cells take advantage of the flexibility of the flagellar hook to generate a turn, may represent the evolutionarily cheapest bacterial motility pattern and a highly beneficial solution to foraging in resource-poor marine environments. [Preview Abstract] |
Tuesday, November 22, 2011 5:02PM - 5:15PM |
S29.00010: Investigation of the Swimming and Flagellar Dynamics of Shear guided Motile Alga Anwar Chengala, Miki Hondzo, Jian Sheng We examine the behavior of force-free swimming cell in a shear flow having spheroidal bodies with two flagella located at the anterior part of the cell that uses breast-like motion for its propulsion. The cell, \textit{Dunaliella primolecta}, displays a unique behavior of propelling along the local vorticity direction in a linear shear flow. The cell rotation is absent during this display and the flagella beating is observed to be asynchronous. The forces and moments generated by the flagella are estimated numerically. Based on the Resistive Force Theory approach, we attempt to demonstrate that the moments generated by beating flagella and their alignment to flow are necessary to counter-act the vorticity of the flow. In addition, we explore the various mechanisms that cell may use to re-orient while in a shear flow as well as how critical the variations in the flagellar beating pattern are to a cell's swimming dynamics. [Preview Abstract] |
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