Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T04: Locomotion, Cilia and Flagella |
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Chair: Maria Tatulea-Codrean, University of Cambridge Room: Ballroom D |
Monday, November 25, 2024 4:45PM - 4:58PM |
T04.00001: Trypanosoma swims with a unidirectionally rotating body and a bidirectionally rotating flagellum Shuang Zhou, Sizhe Cheng, Becca Thomases, Michele Klingbeil, Devadyouti Das The motility of Trypanosoma Brucei (TB), a parasite causing sleeping sickness in mammals, is difficult to quantify, since its rapid and complex body motion challenges conventional microscopy techniques. In this study, by tracking the 3D motion of fluorescent particles attached to their body using out-of-focus diffraction patterns, we are able to obtain high-frame-rate data on the TB deformation dynamics. Our results indicate that TB exhibits a unique locomotion pattern consisting of three distinct components: unidirectional rotation, oscillatory rotation, and flagellar bending. The combined azimuth oscillation and bending propagate a kink wave along the flagella, which drives TB forward. The unidirectional rotation of the TB body is due to its chiral body-shape undergoing a translation. The amplitudes of both the azimuthal oscillation and bending decrease from the anterior to the posterior end, due to the conservation of linear and angular momentum. Numerical simulations produce quantitatively agreeing results. Understanding the biomechanics of TB swimming will allow us to further decipher their unique self-propulsion mechanism in complex environments and flow conditions. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T04.00002: Bundling instability of lophotrichous bacteria in fluids Sookkyung Lim, Jeungeun Park, Yongsam Kim, Wanho Lee, Veronika Pfeifer, Valeriia Muraveva, Carsten Beta We present a mathematical model of lophotrichous bacteria, motivated by Pseudomonas putida, which swim through fluid by rotating a cluster of multiple flagella extended from near one pole of the cell body. Although the flagella rotate individually, they are typically bundled together, enabling the bacterium to exhibit three primary modes of motility: push, pull, and wrapping. One key determinant of these modes is the coordination between motor torque and rotational direction of motors. The computational variations in this coordination reveal a wide spectrum of dynamical motion regimes, which are modulated by hydrodynamic interactions between flagellar filaments. These dynamic modes can be categorized into two groups based on the collective behavior of flagella, i.e., bundled and unbundled configurations. For some of these configurations, experimental examples from fluorescence microscopy recordings of swimming P. putida cells are also presented. Furthermore, we analyze the characteristics of stable bundles, such as push and pull, and investigate the dependence of swimming behaviors on the elastic properties of the flagella. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T04.00003: Hydrodynamic synchronization of rotating flagella with complex torque-speed dependence Maria Tatulea-Codrean, Natasha Diederen Hydrodynamic interactions are a known mechanism for the synchronization of cilia and flagella. Typically, the fluid flow communicates information between the two oscillators, while the elastic compliance of the oscillating units (either flexible filaments, or rigid objects with a flexible anchoring) provides the adaptability necessary for synchronization. Nevertheless, previous studies have shown that rigid objects rotating on fixed trajectories can also synchronize if driven by a phase-dependent forcing. These models are suitable for describing the power and recovery strokes of eukaryotic cilia, but do not apply to bacterial flagella which rotate continuously under a phase-independent driving torque. Instead, the torque generated by the bacterial flagellar motor depends on the rotation speed of the motor. Motivated by the empirical torque-speed relationship of the bacterial flagellar motor, we investigate whether hydrodynamic interactions combined with a speed-dependent (rather than phase-dependent) forcing can lead to synchronization, and we analyse our findings in relation to the existing literature on flagellar synchronization. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T04.00004: A Macroscopic Model for the Collective Dynamics of Bacterial Flagellar Bundles Chijing Zang, Xiang Cheng, Moumita Dasgupta Flagellated bacteria such as E. coli swim by rotating a helical rod-shaped propeller composed of a bundle of multiple flagella. Although the swimming of flagellated bacteria has been extensively studied, most existing studies treat the flagellar bundle as a single rotating helix. Understanding the precise coordination of flagellar dynamics within a bundle is still challenging, due to the complication associated with the interplay of hydrodynamic, elasto-hydrodynamic, and steric interactions at nanometer-scale distances. Here, we experimentally investigate the collective dynamics of multiple flagella by constructing a macroscopic scale model of a flagellar bundle. Specifically, we rotate centimeter-scaled helical filaments in high-viscosity silicone oil with mechanical motors mimicking the features of bacterial flagellar motors. We examine the flow fields induced by rotating flagella at various distances and phase differences and measure the torque of the bundle. Our study sheds light on the hydrodynamic principles governing the collective dynamics of bacterial flagella, placing a crucial missing piece in the puzzle of the locomotion of flagellated bacteria. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T04.00005: Bend It Like A Flagellum Adnan Morshed, Ricardo Cortez, Lisa J Fauci Flagellar motion at low Reynolds number presents a wide variety of mathematical problems that have been addressed over past decades. Swimming dynamics and navigation through tubular confined spaces present challenges in modeling, because, unlike confinements by infinite planes or spheres, fundamental solutions to Stokes equations are not readily expressed. In this work, we present a framework to study flagellar motion in narrow and tortuous tubular enclosures. The basic swimmer is modeled using Kirchhoff rods with regularized Stokeslet segments while the rigid surfaces that constitute the enclosure are represented by regularized Stokeslet surfaces. Swimming kinematics is not prescribed, rather is emergent from time-varying local prescribed curvatures. This approach allows for swimmer-wall interactions and in turn, the evolution of swimming behavior near rigid boundaries of arbitrary shapes. We also investigate the effects of changing environmental variables (fluid viscosity, tube diameter, etc.) and flagellum parameters (e.g., length, stiffness, etc.) on swimming performance and navigational success through bends. Both aspects have profound implications for understanding the coevolution of female reproductive tracts and sperm morphology and kinematics in different organisms.
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Monday, November 25, 2024 5:50PM - 6:03PM |
T04.00006: Analyzing Changes in Flagellar Shape and Swimming Speed with Varying Fluid Viscosity Kelli E Loritsch, Robert D Guy, Becca Thomases Many different microswimmers propel themselves using flagella that beat periodically. The shape of the flagellar beat and swimming speed have been observed to change with fluid rheology. We quantify changes in the flagellar waveforms of Chlamydomonas reinhardtii in response to changes in fluid viscosity using (1) shape mode analysis and (2) a full swimmer simulation to analyze how shape changes affect the swimming speed. By decomposing the gait into the time-independent mean shape and the time-varying stroke, we find that the mean shape of the flagellum changes in response to viscosity, while the time-varying stroke does not. Using the swimmer simulation, we show that the observed change in swimming speed with viscosity is explained by the variations in mean flagellar shape and beat frequency. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T04.00007: Thrust dynamics of hairy flagella with three-dimensional wave pattern Jens Honore Walther, Saeed S Asadzadeh, THOMAS KIØRBOE The pivotal role of unicellular flagellates in aquatic food webs is facilitated by their flagella that generate thrust for propulsion and feeding current generation. In important flagellates, the flagellum is equipped with rigid hairs that reverts thrust direction and increases its magnitude by a factor 5-10 relative to a naked flagellum. We understand how this functions in flagella with planar waves, but many flagellates have three-dimensional wave patterns. Here we show that a wave of twist and torsion of alternating sign propagating along the beating flagellum is required to yield thrust of the magnitude observed in living cells. The resulting dynamic rotation of the densely spaced hairs yields a flapping pattern that drives an efficient feeding current in a dominating group of oceanic flagellates. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T04.00008: Adaptive flagella beats select phototaxis modes in Chlamydomonas reinhardtii Alan Cheng Hou Tsang Many biological microswimmers modulate their flagella beats in response to environmental stimuli to exhibit complex navigation strategies. In this talk, we will discuss how Chlamydomonas reinhardtii adaptively switch their flagella beats in response to light to select different phototaxis modes (e.g., positive and negative phototaxis). We tracked individual cells and experimentally verified that the switching of flagella waveform and the modulation of flagella phase differences are the key mechanisms for phototaxis transitions. We will discuss a hydrodynamic model that connects photoreception and flagella beat modulation to capture the phototaxis transition. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T04.00009: Modeling Fluid Flow of Free-Swimming Algae Using Modified Three-Sphere Models Md Iftekhar Yousuf Emon, Gregorius Rangga Wisnu Pradipta, Xiang Cheng, Xin Yong Chlamydomonas reinhardtii, a motile species of green algae, rhythmically beats its flagella to transport ambient fluid, generating propulsion for locomotion and facilitating interactions with other microorganisms. A minimal three-sphere model, designed to reflect the basic symmetry and flagella beating mode of C. reinhardtii, has been extensively used to study various aspects of algal swimming dynamics, including flagellar synchronization, run-and-tumble behavior, response to shear flow, and rolling motion. Despite these successes, the detailed flow field generated by this model has not been thoroughly investigated. In this study, we systematically examine both the time-averaged and time-resolved fluid flows of the three-sphere model and compare the model predictions against 2D and 3D experimental measurements. Our results indicate that the current model does not capture the characteristic flow features observed experimentally. To address this, we develop a modified three-sphere model incorporating new beating features and analyze their impact on flow field predictions. This study provides crucial insights into the accurate modeling of hydrodynamics in algal swimming. |
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