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 L03: Low Reynolds Swimming II: Directed Motion and Complex Environments |
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Chair: Meisam Zaferani, Princeton University Room: Ballroom C |
Monday, November 25, 2024 8:00AM - 8:13AM |
L03.00001: Harnessing diffusiophoresis to improve the bacterial motility toward toxic pollutants Viet Sang Doan, Ali Nikkhah, Sangwoo Shin In bioaugmentation, which requires delivering decomposer bacteria to contaminated soil micropores, chemotaxis has been identified as an advantageous strategy for directing the bacteria toward toxic pollutants. However, the complex microenvironment of the soil matrix often restricts bacterial movement, effectively hindering the remediation process. In this study, we investigate diffusiophoresis as a means to improve the chemotactic motility of soil bacteria toward the pollutant source. We examine the response of Pseudomonas putida F1, a flagellated soil bacterium, to salt (diffusiophoresis) and toluene (chemotaxis) gradients, and a combination of both. We observe that diffusiophoresis significantly influences bacterial run-and-tumble behavior, resulting in straighter trajectories during runs while tumbling less. Our results indicate that diffusiophoresis can improve the ability of P. putida to reach the chemoattractant in confined geometries, offering a promising strategy for bioremediation in contaminated soil environments. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L03.00002: Unravelling the mechanisms of gradient of antibiotic sensing by bacteria. Richa Karmakar, Neha Rani Das, Anwita Sarkar, Aswin R, Deblina Chowdhury, Saarwani Komanduri, Madhurima Koley, Aakanksha Venkateswar, Pushpavanam Subramaniam Motile bacteria may exhibit chemotactic responses by detecting chemical gradients using chemoreceptors. These receptors relay signals that guide bacterial movement towards or away from certain compounds. Bacteria are often exposed to the gradient of antibiotics, which can create selective pressure. To combat this situation, bacteria develop resistance to the antibiotic. Although many bacterial species exhibit surface motility and/or swimming motility, our understanding of how these antibiotic gradients influence their movement is surprisingly limited. In this work, we evaluate how the bacteria respond in the presence of antibiotic gradient. For this experiment, we use Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis and different fluoroquinolone groups of antibiotics (Levofloxacin, Ofloxacin, and Norfloxacin). To understand the chemotactic behaviour of the population of bacteria, we perform the soft agar plate assay, and for single bacteria, we use the capillary assay. Chemotaxis of wild-type bacterial strains on a soft agar plate was analysed in terms of expansion speed, which is computed by taking the outer ring radius and time of incubation. Wildtype susceptible strains were repelled by antibiotics discs, thereby forming a zone of clearance, whereas resistant strains traversed towards the discs. In capillary assay, the bacteria are exposed to a stable linear gradient, and the result depicted that the antibiotics act as chemoattractants. Upon doing the gradient quantification, it was very evident that the bacteria showed bi-phasic sensing behaviour, both attraction and repulsion to the same chemical depending on its concentration when exposed to the antibiotic gradient. At low concentrations of an antibiotic, E. coli exhibits a positive chemotactic response, where the bacteria are attracted towards the source of the chemical. At high concentrations, the antibiotic triggers a negative chemotactic response, causing the bacteria to move away from the source. This is due to saturation of the chemoreceptors or activation of different signalling pathways that lead to repulsion. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L03.00003: Effects of chemical gradients on the chemotactic motility of Escherichia coli Ali Nikkhah, Viet Sang Doan, Sangwoo Shin Bacterial chemotaxis is a behavior in which motile cells navigate toward food sources or away from toxins, playing a crucial role in their survival. For Escherichia coli and many other species, this movement is typically characterized by undergoing a biased run-and-tumble process along the chemical gradients. In this study, we investigate the chemotactic motility of E. coli under multiple chemical gradients where the cells are subjected to chemoattractant and salt gradients. Using a microfluidic device capable of introducing salt and chemoattractant gradients simultaneously, we observe a drastic change in the swimming behavior, where the cells experience improved motility due to the synergistic effect of chemotaxis and diffusiophoresis. The changes in the swim orientation, run straightness, run speed, and tumble frequency lead to a more robust migration of bacteria toward the chemoattractant. Our findings highlight the potential utility of diffusiophoretic transport in guiding the cells in drug delivery and bioremediation systems. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L03.00004: Chemotactic smart microswimmers Yangzhe Liu, On Shun Pak, Alan C. H. Tsang In this talk, we will discuss how reinforcement learning can endow a model three-sphere microswimmer with the capability to search for chemical sources based on localized cues. We will discuss the observed chemotactic behaviors of these smart microswimmers compared with those observed for biological cells. Our findings pave the way for developing microswimmers that can autonomously navigate complex, unpredictable environments. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L03.00005: Sperm migration in complex environments Meisam Zaferani, Christina Kurzthaler, Howard A Stone To fertilize the oocyte, sperm must navigate the complex and fluctuating environment of the female reproductive tract (FRT), surviving intensive selective pressures, undergoing physiological transitions, and searching for the oocyte. This inefficient long-distance migration, where only one sperm succeeds from billions, along with a poor statistical understanding of sperm motility, complicates the development of a comprehensive physical model. Here, we perform motility profiling for chemically stimulated bull sperm over extended periods and conduct stochastic simulations to propose a three-phase model for sperm migration inspired by a previous model for bird navigation. Our results reveal three phases of migration: 1) a long-distance phase with ballistic motion receiving directional cues, 2) an exploration phase with persistent random walks for navigating complex geometries, and 3) an exploitation phase with localized chiral swimming for target pinpointing. We also identify a mixed-phase indicating a smooth transition or trade-off between exploration and exploitation. This model offers a potential explanation for sperm migration in the FRT and could inform the next generation of assisted reproductive technologies. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L03.00006: Invasion of Bacteria Swimming Upstream in Structured Microchannels Ran Tao, Suya Que, Albane Théry, Arnold JTM Mathijssen Bacteria can swim upstream in narrow channels, causing the contamination of biomedical devices and urinary tract infections (UTIs). Despite these implications for human health, this reorientation against flows remains underexplored in structured environments. Here, we investigate experimentally and theoretically how E. coli bacteria invade microfluidic channels with different architectures. By tracking single cells under different flow conditions, we reveal the three-stage dynamics of bacterial invasion: entering microchannels, propagating upstream, and escaping to enter the next one. Our results show how the channel size and shape significantly influence each of these contamination stages. Additionally, we explore how these processes affect bacterial collective motion and biofilm formation upstream. Our research guides the design of anti-invasion strategies for biomedical devices and sets the foundation for understanding microbial navigation in environmental flow networks. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L03.00007: Impact of Dead-End Pores on Directed Magnetotactic Bacterial Motility Max D Liljenstolpe, Louison Thorens, Jeffrey S Guasto Understanding the physical mechanisms regulating microorganism navigation through porous networks is critical for a wide range of biological and industrial applications. Despite their recognized importance, relatively little is known about the influence of dead-end pores on the directed motility of swimming cells, and how such micro-scale interactions impact macro-scale transport properties. Here, we precisely track the motility of magnetotactic bacteria (MC-1) directed via an external magnetic field into microfluidic model dead-end pores. The spatial distributions and escape rates of the bacteria are experimentally characterized for various pore sizes, pore shapes, and magnetic field strengths. The results are validated through simulations and supported by scaling analysis. Furthermore, we illustrate the effect of individual motility on bulk transport by measuring the transport coefficients of magnetotactic bacteria in both random porous media and arrays of engineered pores. These results may inform our understanding of physical ecology in marine sediments, as well as the design of bioremediation and targeted drug delivery processes. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L03.00008: Abstract Withdrawn
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Monday, November 25, 2024 9:44AM - 9:57AM |
L03.00009: Durotaxis in viscoelastic fluids Vaseem A Shaik, Jiahao Gong, Gwynn J Elfring Active particles often navigate through inhomogeneous environments, where they display directed motion known as taxis by swimming up or down the gradients of inhomogeneities. Well-known types of taxis include chemotaxis in chemical or nutrient gradients, phototaxis in light gradients, rheotaxis in fluid velocity gradients, and viscotaxis in viscosity gradients. Another example is durotaxis, which is the movement of cells on a substrate in the direction of stiffness gradients. Here we report an analogue of durotaxis in fluids, demonstrating directed motion of active particles in the gradients of stiffness (or relaxation timescale) of a viscoelastic fluid. This work provides insights into the dynamics of active particles in inhomogeneous viscoelastic fluids, and the taxis identified here could be exploited to sort active particles by probing the inhomogeneities. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L03.00010: Self-diffusiophoretic spheroid in a shear-thinning fluid Yi Man, Guangpu U Zhu, Brandon Van Gogh, Lailai Zhu, On Shun Pak Shear-thinning viscosity is a non-Newtonian behavior commonly found in biological fluids like blood and mucus. Its impact on the propulsion of active particles has garnered significant interest. It was shown that spherical Janus particles driven by self-diffusiophoresis always swim slower in a shear-thinning fluid than in a Newtonian fluid. In this talk, we move beyond the spherical limit to discuss the effect of particle geometry on self-diffusiophoretic propulsion in a shear-thinning fluid. Via asymptotic analysis and numerical simulations, we demonstrate that shear-thinning rheology can enhance the propulsion of spheroidal particles, in contrast to previous findings for spherical particles. We also present symmetry arguments to elucidate some new features emerging from the combined effect of anisotropy of the spheroidal geometry and nonlinear fluid rheology. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L03.00011: Drag and Thrust of a Helical Swimmer in a Yield Stress Fluid Farshad Nazarinasrabad, Hadi Mohammadigoushki The locomotion of microorganisms is a common phenomenon in diverse biological environments and significantly influences human health. For instance, the mobility of Helicobacter pylori (H. pylori) through gastric mucus, yields ulcers and other diseases. Recent experimental studies indicate that H.pylori gets immobilized when the surrounding environment (mucus) behaves like a yield stress fluid. In our earlier study, for the first time, we characterized three stages of locomotion observed in yield stress fluids. In this study, we explore the forces involved in these swimming stages by assessing both thrust and drag forces exerted by the swimmer under different conditions like the shape of the head and surface roughness in yield stress fluids. Using a custom-made rotational Helmholtz-coil, a constant torque is imposed on the swimmer that generates the rotational motion (Ω) . Our experiments found that as Bingham number (Bi=τy/(ηΩ)) decreased, pressure forces on the swimmer decreased linearly, while thrust from the helical tail rose. For pitch angles (ψ) of 12-32°, the thrust was lower than pressure, implying no net motion. below critical Bi (Bic ≈0.6), thrust surpassed pressure. Swimmers with ψ ≥ 37° consistently exceeded pressure with thrust. Additionally, we observed significant drag forces on the head, influenced by swimmer geometry and surface roughness. The drag coefficient increased as increased and leveled off at a higher Bi . |
Monday, November 25, 2024 10:23AM - 10:36AM |
L03.00012: Swimming motion of flagellated bacteria in yield stress fluids Sabarish V V. Narayanan, Donald Lyle Koch, Sarah Hormozi We conduct a numerical study of the swimming motion of a flagellated bacterium in a concentrated polymer solution exhibiting finite yield stress and viscoelasticity. The concentrated polymer solution has a microstructure at the length scale of the flagellar bundle diameter, and a two-fluid model is used to capture its effect on the motion. We investigate the effects of viscoelasticity, shear thinning, and yield stress combined with microstructure on the swimming motion of a bacterium. We find that, at small polymer concentrations and relaxation times, the enhancement in swimming velocity, observed in several experiments, predominantly arises from the microstructure in the medium. For fluids with finite yield stresses, a larger resistance to motion results in smaller steady swimming velocities compared to those in fluids with no yield stress. It is also observed that, in fluids with a given yield stress, increasing elasticity of the medium leads to an increase in the steady swimming velocity. Finally, we comment on the effect of viscoelasticity and yield stresses on the trajectory of a swimming bacterium. |
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