Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L24: Swimming, Motility, and LocomotionLive
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Sponsoring Units: DFD Chair: Daphne Klotsa, Univ of NC - Chapel Hill |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L24.00001: Collective Dynamics of Multicellular Magnetotactic Bacteria Alexander Petroff, Benjamin Roque, Alejandra Rosselli Multicellularity has evolved in at least twenty-five lineages. Among the bacteria, only one a group of δ-proteobacteria called ``Multicellular Magnetotactic Bacteria'' (MMB) are obligately multicellular. These bacteria live in aggregates composed of 10--60 individual cells, which quick die if removed from the aggregate. Each cell in the aggregate has about 30 flagella, normal to the outer surface of the aggregate. Although each cell pushes the aggregate in a different direction, the cells exert a total force that is parallel to the aggregate's net magnetic moment, typically to within a few degrees. Amazingly, cells are able to coordinate their motility even as they grow and divide, new magnetic crystals are formed, and the aggregate elongates and divides. Here we examine how physical interactions between cells in a proto-multicellular aggregate allow them to coordinate their growth and motion before the evolution of shared chemical signaling pathways. We first present experimental observations of the motion of a single aggregate and discuss how cells in the aggregate coordinate their motility. We then examine the collective dynamics of a swarm of these multicellular bacteria. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L24.00002: Adaptive cell-cell communication enhances bacterial chemotaxis Soutick Saha, Sean Fancher, Andrew Mugler Bacteria track chemical gradients using a biased random walk, a process called chemotaxis. Recent experiments suggest that bacteria also communicate during this process. Using mathematical modeling and computer simulation, we find that sufficiently strong communication succeeds in keeping a population of bacteria together, but actually slows down chemotaxis. However, if communication strength is adapted to the level of the external chemical, we find that chemotaxis is instead sped up. We apply our findings to E. coli, where both communication and cell-to-cell variability play an important role. Using experimental data to calibrate the model, we predict that adaptive communication and cell-to-cell variability can synergistically increase chemotaxis speed. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L24.00003: A proprioceptive mechanism for swimming Jesús Sánchez Rodríguez, Christophe Raufaste, Mederic Argentina Aquatic animals exhibit a tremendous diversity in physiology and in shape, consequently, this implies a huge variation of gaits in animals for achieving locomotion. Nevertheless, we expect general mechanisms at play because all the movements result from a drag-thrust balance. While learning to swim, we ascertained that an efficient locomotion is strongly dependent on the synchronisation of the muscle activation with respect to the dynamics of the surrounding fluid. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Not Participating |
L24.00004: Single proton torque generation in Escherichia coli Ilyong Jung Escherichia coli (E. coli) is an unicellular microorganism that lives in human intestines. The locomotion of this bacteria is powered by one or more long bacterial flagellar motors, ~ 45 nm molecular nano machines. The bacterial flagellar motor, which converts a proton-motive force to flagellar rotation, plays an important role in various biological phenomena such as chemotaxis, cell swarming over a surface, and bacterial pathogenicity. It also attracts a growing interest as a framework for a potential target for drug development countering human disease. However, despite its biological significance, the mechanism that underlies the torque generation of the bacterial flagallar motor still remains elusive. Our preliminary results show that single proton may be enough to generate torque of the bacterial flagellar motors. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L24.00005: Substrate Stiffness tunes the dynamics of polyvalent rolling motors Chapin Korosec, Lavisha Jindal, Mathew Schneider, Igacio Calderon de la Barca, Martin J. Zuckermann, Nancy R Forde, Eldon Emberly Nature has evolved many mechanisms for achieving directed motion on the subcellular level. The burnt-bridges ratchet (BBR) is one mechanism used to achieve superdiffusive molecular motion over long distances through the successive cleavage of surface-bound energy-rich substrate sites. The BBR mechanism is utilized throughout Nature: it can be found in bacteria, plants, humans, as well as non-life forms such as influenza. Recently, experimentalists have succeeded in creating synthetic versions of spherical BBRs. Experimental progress on both the synthetic and biological fronts has led to contradictory explanations as to the mechanistic origin for the observed velocities and directional persistence found for spherical BBR systems. In this talk I will discuss our recent findings that substrate stiffness influences the motor-like properties (eg. speed, processivity, superdiffusivity, and the dynamical mode) of BBRs. Our work has implications for the mechanism by which the influenza virus navigates pericellular space to infect cells, as well as provides a distinct example of an active matter system where directed motion arises from collective effects of substrate cleavage by individual coupled model enzymes. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L24.00006: Strong Confinement of Swarming Bacteria on Surfaces Irakli Gudavadze, Ernst-Ludwig Florin Bacterial swarming is a rapid, collective movement of bacteria over a surface powered by rotating flagella [1]. Unlike swimming, swarming takes place in thin liquid films, constraining bacteria to two dimensions. So far, it always has been assumed that the film is thicker than the diameter of a bacterium, but its exact thickness has never been measured. Here we present a novel method for measuring film thickness with tens of nanometer precision. For Bacillus subtilis colonies grown on agar gels, we find film thicknesses as thin or even thinner than the diameter of a single bacterium. For thicknesses thinner than a single bacterium, surface tension forces are expected to be on the order of tens of nanonewtons. Considering swimming bacteria experience drag force of about half a piconewton [2], surface associated bacteria face orders of magnitude stronger resistive force even if we assume small frictional coefficients of between bacteria and the agar gel surface. It remains unclear how flagella driven motility can be achieved under such strong confinement. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L24.00007: A Traveling-Wave Solution for Bacterial Chemotaxis with Growth Avaneesh Narla, Jonas Cremer, Terence Tai-Li Hwa Bacterial chemotaxis is among the most extensively characterized phenomena in microbiology. However, a prominent experimental observation, the stable propagation of migratory bands in growth media, has evaded a clear, quantitative understanding. We analyze a simplified version of the GE model introduced by Cremer and Honda et al. which identified distinct roles played by chemotaxis and cell growth. We heuristically obtain an analytical expression, verified by numerical results, for the expansion speed of the migratory band, c, in terms of the key cellular and environmental parameters. We find c to increase linearly with chemotactic motility, turning over to a square root dependence for motility exceeding the attractant diffusivity. Further, c increases as the square root of the growth rate, amplified by the ratio of the ambient attractant concentration and the attractant detection limit, peaking at intermediate concentrations determined by the carrying capacity. In contrast, c is only weakly dependent on attractant uptake, commonly considered a key determinant of population expansion by chemotaxis. Finally, we relate the GE model to the F-KPP equation which describes population expansion due to growth and cellular diffusion in the absence of chemotaxis. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L24.00008: Efficient bio-inspired swimming with hybrid actuation Ersan Demirer, Oluwafikayo Abisola Oshinowo, Alexander Alexeev Conventional designs of bio-inspired robotic swimmers involve the oscillations of a caudal fin through an external actuation source to generate heaving motion. Recent advances in piezoelectric materials allow the fabrication of bio-inspired fins with an internal mode of actuation such as a distributed bending moment. Through three-dimensional computer simulations, we probe the effects a combined internal and external actuation of elastic fins on their hydrodynamic performance. The fin is modelled as a rectangular elastic plate, actuated at its root by a harmonic heaving motion and through its length by a distributed internal bending moment. We probe the effects of the phase lag between the external and internal actuation on the hydrodynamic thrust and efficiency. We show that the combined actuation can be tuned to work in synergy yielding thrust and efficiency that outperform each of actuation methods. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L24.00009: A Novel Rheotaxis-based Microfluidic Device for Selecting Sperm from Semen Infected with Viruses Afrouz Ataei, Md Alamgir Kabir, Andy Lau, Waseem Asghar Prolonged exposure of spermatozoa to seminal plasma has been found to have adverse effects on sperm function such as motility and vitality. Recent studies have shown that the presence of HIV, hepatitis B (HBV) or Zika virus (ZIKV) in semen impairs sperm parameters and in particular reduces motility. These viral infections are considered as a negative effect on male reproductive function and infection can be transmitted to the partners and newbornes. Sperm washing process, which is the standard procedure in infertility treatment, is a form of sperm preparation that is required prior to intrauterine insemination (IUI) or in vitro fertilization (IVF), because it removes chemicals from the semen, which may cause adverse reactions in the uterus. Moreover, sperm washing process is increasingly essential to decrease the risk of virus transmission before using it for IUI or IVF. The objective of this study is to show that the presented rehotaxis-based microfluidic device is capable of washing out the sperm cells during the process of selecting healthy sperm for assisted reproductive technology (ART). We demonstrate that sperm selected and washed with this device at a specific flow rate does not contain any viruses. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L24.00010: Dynamic markers of C. elegans locomotion in three dimensions Susannah Grace Zhang, Asia Baker, Katherine Canavan, Jenny Magnes, Harold Hastings We characterize some key features of the locomotion of Caenorhabditis elegans (C. elegans) in its natural (3D) environment. C. elegans, a small (1 mm) nematode is widely studied and used as model organism in the neuroscience community (“Wormbook,”http://www.wormbook.org) because it is a “complete microorganism” with a relatively small, fully described nervous system.The locomotion of C. elegans in 2D environments has been widely studied (19,600 references in Google Scholar search on 10/02/2020) and well understood since Pierce-Shimomura, Morse and Lockery (1999). The motion of C. elegans is captured with diffraction microscopy (Magnes, Susman and Eells, 2012). In particular, diffraction imaging responds to changes in the shape of C. elegans. The diffraction signal at one point yields a time series, and thus an attractor in typically 4D space (using mutual information and false nearest neighbors techniques for Takens embedding). We find a positive Lyapunov exponent of 1.3/ s, a marker of deterministic chaos, larger than the value of 0.7/ s found by Ahamed, Costa and Stephens (2019) for motion in 2D. Finally, we see complex dynamics on multiple time scales in recurrence plots of 3D motion, as seen earlier for 2D motion by Stephens et al. (2011). |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L24.00011: Centipede locomotion on rough terrain Eva Erickson, Kelimar Diaz, Alexandra Carruthers, Yasemin Ozkan-Aydin, Baxi Chong, Daniel I Goldman Multi-limbed invertebrates such as centipedes negotiate diverse environments via propagation of coordinated travelling waves of body and limb flexion. While progress has been made studying how these animals locomote on flat terrain, less is known about their navigation in complex environments. Here we challenged S. polymorpha (N=4, L = 7.7±1.5 cm, 19 joints and leg pairs) to transverse a flat frictional surface and Gaussian-distributed rough terrains (12 x 24 cm2 with variable height of blocks ranging from 0 to 1.5 cm). On the flat frictional surface, centipedes moved at speeds of 1.44±0.54 body lengths per second (BL/s) by generating a traveling wave along their limbs and bodies, maintaining a constant phase shift between these two waves. On the rough terrains, the centipedes moved at speeds of 1.79±0.45 BL/s and 0.77±0.51 BL/s for lower and higher roughness, respectively. Unexpectedly, wave dynamics were similar on flat ground and the lower roughness terrain. Traversal of the rough terrains was facilitated by passive limb bending when in contact with blocks of different heights. Centipedes negotiated collisions with blocks by passively gliding their limbs to resume locomotion. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L24.00012: Wiggling organisms use geometry to swim in curved spaces Brian Day, Elisabetta Matsumoto In euclidean space, deformable objects are able to generate body rotations -- such as a cat always landing on its feet -- but not translations. This restriction is lifted when a space possesses intrinsic curvature. A consequence of transporting vectors in curved space is holonomy. Holonomy measures differences between a vector and its copy after being transported in a closed loop. Holonomic effects and the fact that center of mass is ill-defined in curved space combine to allow for net translations of objects through body deformations. This is analogous to how microorganisms self-propel themselves in low Reynolds number fluids. Using an implicit integrator, we investigate the dynamics produced by the deformation cycles of quasi-rigid deformable bodies for select 3D riemannian manifolds. Particularly, we consider the stroke efficiency for various deformation cycles. The symmetries of the space provide conservation laws to inform the deformations cycles, however when no symmetries are present it is more complicated. For curved spaces lacking symmetry, we exchange extendable rod connectors with hookian springs to try and produce motion generating body deformations. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Not Participating |
L24.00013: Negative bacterial chemotaxis induced by surface interaction Christian Esparza Lopez, Eric Lauga Bacterial chemotaxis is the ability of cells to bias their movement in response to chemical signals. Among the species of chemotactic bacteria, E. coli is the most studied and its strategy is now well documented. When free swimming in a quiescent fluid, E. coli cells move in quasi-rectilinear trajectories (runs), interrupted by quick reorientations (tumbles). In response to certain amino acids, the length of the bacterial runs are biased and, as a result, the cell effectively drifts towards high concentration regions of chemoattractant. Although it is an efficient search strategy in quiescent fluids, chemotaxis can be disrupted in a shear flow due to an induced rotation of the cell body. Swimming bacteria are often found in confined environments, and hydrodynamic interactions with surfaces may hinder chemotaxis in a similar fashion as shear flow does. In this study we explore theoretically the effects of near-surface swimming on E. coli chemotaxis in the small gradient regime. We show in particular that negative chemotaxis can be induced by a change in the curvature of the cell trajectories. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L24.00014: Scattering of a fast-swimming bacterium off of a surface Schuyler McDonough, Benjamin Roque, Alexander Petroff The sediment bacterium Thiovulum majus is one of the fastest known |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L24.00015: Hydrodynamic interactions in bundles of bacterial flagella Maria Tatulea-Codrean, Eric Lauga Flagellated swimming is an important and well-studied aspect of prokaryotic life. It is also the more "socially-distanced" form of bacterial motility, usually taking place in the bulk of the medium, compared to gliding which takes place on crowded surfaces. Bacterial flagella are composed of a slender and semi-rigid helical filament, a flexible hook, and a molecular motor which rotates continuously in order to escape the reversibility of Stokes flow and push the cell forward. The molecular motor may change the sense of rotation to induce a change in swimming direction, either through a run-reverse or run-reverse-flick mechanism for bacteria with a single flagellum, or run-and-tumble in the case of multi-flagellated bacteria like E. coli. Apart from this simple, stochastic control over the molecular motors, bacteria cannot control the individual position of flagella, so much of their swimming behaviour results naturally from steric and hydrodynamic interactions with nearby surfaces, between the flagella and cell body, or amongst the flagella themselves. We will present novel theoretical findings regarding the effect of inter-filament hydrodynamic interactions on thrust generation and synchronization in bundles of bacterial flagella. |
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