Hydrodynamic Interactions, Hidden Order, and Emergent Collective Behavior in an Active Bacterial Suspension

Pierce, Christopher; Wijesinghe, Hiran; Mumper, Eric; Lower, Brian H.; Lower, Steven K.; Sooryakumar, R.

doi:10.1103/physrevlett.121.188001

Cited by 23 publications

(23 citation statements)

References 35 publications

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“…In particular, the pearling hydrodynamic instability reported by Waisbord et al [38], the velocity condensation [39] and the emergence of new phases induced by a magnetic field [40] are striking examples of these.…”

Section: Introductionmentioning

confidence: 96%

Magnetotactic bacteria in a droplet self-assemble into a rotary motor

et al. 2019

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From intracellular protein trafficking to large-scale motion of animal groups, the physical concepts driving the self-organization of living systems are still largely unraveled. Self-organization of active entities, leading to novel phases and emergent macroscopic properties, recently shed new light on these complex dynamical processes. Here we show that under the application of a constant magnetic field, motile magnetotactic bacteria confined in water-in-oil droplets self-assemble into a rotary motor exerting a torque on the external oil phase. A collective motion in the form of a large-scale vortex, reversable by inverting the field direction, builds up in the droplet with a vorticity perpendicular to the magnetic field. We study this collective organization at different concentrations, magnetic fields and droplet radii and reveal the formation of two torque-generating areas close to the droplet interface. We characterize quantitatively the mechanical energy extractable from this new biological and self-assembled motor.

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Section: Introductionmentioning

confidence: 96%

Magnetotactic bacteria in a droplet self-assemble into a rotary motor

et al. 2019

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“…The model is non-dimensionalised using characteristic length scale , velocity and dynamic viscosity . For comparison with experiments, we use a characteristic bacterium size 32 . Steric interactions are included using soft pair-repulsive forces 43 between the centres of each bacteria.…”

Section: Resultsmentioning

confidence: 99%

“…A thorough understanding of the individual and collective properties of MTB is thus needed to fully exploit their potential for practical applications. The wall-mediated behaviour of single and pairs of MTB has been explored 31 , and attractive hydrodynamic interactions lead to clustering near a wall 32 . Various patterns and instabilities can be induced by the control and orientation of large swimmer populations 33 , including pearling of focused MTB in a thin capillary 34 , 35 or vortex formation in droplets 36 .…”

Section: Introductionmentioning

confidence: 99%

Self-organisation and convection of confined magnetotactic bacteria

Théry

Nagard

Ono-dit-Biot

et al. 2020

Sci Rep

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Collective motion is found at all scales in biological and artificial systems, and extensive research is devoted to describing the interplay between interactions and external cues in collective dynamics. Magnetotactic bacteria constitute a remarkable example of living organisms for which motion can be easily controlled remotely. Here, we report a new type of collective motion where a uniform distribution of magnetotactic bacteria is rendered unstable by a magnetic field. A new state of "bacterial magneto-convection" results, wherein bacterial plumes emerge spontaneously perpendicular to an interface and develop into self-sustained flow convection cells. While there are similarities to gravity driven bioconvection and the Rayleigh-Bénard instability, these rely on a density mismatch between layers of the fluids. Remarkably, here no external forces are applied on the fluid and the magnetic field only exerts an external torque aligning magnetotactic bacteria with the field. Using a theoretical model based on hydrodynamic singularities, we capture quantitatively the instability and the observed long-time growth. Bacterial magneto-convection represents a new class of collective behaviour resulting only from the balance between hydrodynamic interactions and external alignment.

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“…[1][2][3] These materials exhibit unique mechanical and dynamic features that emanate from their disordered structure. 4,5 Similarly, in some cases, active matter comprised of self-propelled agents remains disordered as it achieves very high densities; examples of such systems include bacterial assemblies, 6 cellular tissues, 7,8 and groups of animals. 9,10 Although active matter is relatively well-studied at low and intermediate densities, 11,12 an important open question is whether the emergent mechanical properties of dense active matter are similar to, or different from, their non-active counterparts.…”

Section: Introductionmentioning

confidence: 99%