Collective motion in a suspension of micro-swimmers that run-and-tumble and rotary diffuse

Krishnamurthy, Deepak; Subramanian, Ganesh

doi:10.1017/jfm.2015.473

Cited by 37 publications

(69 citation statements)

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“…These properties would suggest a hydrodynamic origin of the collective motion, at least in less confined situations, since the largest possible flow structure -set by system size -is predicted to dominate in hydrodynamics based collective motion [8]. Simulations also showed a reduction of the total kinetic energy under confinement at fixed Φ c [58], similar to our experiments. Under stronger confinement (h = 8 µm), the selected eddy size, although fixed, differed from the channel height.…”

Section: Discussionsupporting

confidence: 85%

Chemotactic behaviour ofEscherichia coliat high cell density

Colin¹,

Drescher²,

Sourjik³

2018

Preprint

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4At high cell density, swimming bacteria exhibit collective motility patterns, self-organized through physical 5 interactions of a however still debated nature. Although high-density behaviours are frequent in natural 6 situations, it remained unknown how collective motion affects chemotaxis, the main physiological function 7 of motility, which enables bacteria to follow environmental gradients in their habitats. Here, we systemati-8 cally investigate this question in the model organism Escherichia coli, varying cell density, cell length, and 9 suspension confinement. The characteristics of the collective motion indicate that hydrodynamic interac-10 tions between swimmers made the primary contribution to its emergence. We observe that the chemotactic 11 drift is moderately enhanced at intermediate cell densities, peaks, and is then strongly suppressed at higher 12 densities. Numerical simulations reveal that this suppression occurs because the collective motion disturbs 13 the choreography necessary for chemotactic sensing. We suggest that this physical hindrance imposes a fun-14 damental constraint on high-density behaviours of motile bacteria, including swarming and the formation 15 of multicellular aggregates and biofilms.Indroduction 17 When the cell density of a suspension of swimming bacteria increases, collective motion emerges, char-18 acterized by intermittent jets and swirls of groups of cells [1][2][3]. This behaviour is observed for many 19 microorganisms not only in artificial but also in natural situations, often at an interface, e.g. when bac-20 teria swarm on a moist surface in the lab [4][5][6][7][8] or during infection [9], or at an air-water interface during 21 formation of pellicle biofilms [1, 10]. Bacterial collective motion has been extensively studied experimentally 22 [11][12][13][14] and theoretically [15][16][17][18][19][20], and it is known to emerge from the alignment between the self-propelled 23 cells [21]. Two alignment mechanisms have been proposed, based either on steric interactions between the 24 rod-like bacteria [22][23][24] or on the hydrodynamics of the flow they create as they swim [15, 17], which 25 displays a pusher force dipole flow symmetry [3, 25, 26]. However, the relative importance of these two 26 mechanisms has not been clearly established so far [27]. 27Bacterial collective motion contrasts to the behaviour of individual motile cells in dilute suspension, 28 when bacteria swim in relatively straight second-long runs interrupted by short reorientations (tumbles), 29 resulting at long times in a random walk by which they explore their environment [28]. Bacteria can 30 furthermore navigate in environmental gradients by biasing this motion pattern: they lengthen (resp. 31 shorten) their runs when swimming toward attractive (resp. repulsive) environment [28]. The biochemical 32 signaling pathway controlling this chemotactic behaviour is well understood in E. coli [29, 30] and it is 33 one of the best modeled biological signaling systems [31]. Bacteria monitor -via...

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Section: Discussionsupporting

confidence: 85%

Chemotactic behaviour ofEscherichia coliat high cell density

Colin¹,

Drescher²,

Sourjik³

2018

Preprint

View full text Add to dashboard Cite

show abstract

“…Consideration of a distribution of run times, did account for slightly larger relaxation times observed in the linear response regime [Nambiar et al (2017)], but cannot account for the discrepancy in the non-linear response. A possible explanation for the large observed relaxation times is that at the volume fraction considered, the effective volume fraction is nL 3 = 3.43, at which the suspension has transitioned to a regime of collective motion [Krishnamurthy & Subramanian (2015); Nambiar et al (2017)].…”

Section: Resultsmentioning

confidence: 99%

Stress relaxation in a dilute bacterial suspension: the active–passive transition

Nambiar

Phanikanth²,

Nott³

et al. 2019

J. Fluid Mech.

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This paper follows a recent article of Nambiar et al. (2017) on the linear rheological response of a dilute bacterial suspension (e.g. E. coli) to impulsive starting and stopping of simple shear flow. Here, we analyse the time dependent non-linear rheology for a pair of impulsively started linear flows -simple shear (a canonical weak flow) and uniaxial extension (a canonical strong flow). The rheology is governed by the bacterium orientation distribution which satisfies a kinetic equation that includes rotation by the imposed flow, and relaxation to isotropy via rotary diffusion and tumbling. The relevant dimensionless parameters are the Peclet number Pe ≡γτ , which dictates the importance of flow-induced orientation anisotropy, and τ D r , which quantifies the relative importance of the two intrinsic orientation decorrelation mechanisms (tumbling and rotary diffusion). Here, τ is the mean run duration of a bacterium that exhibits a run-and-tumble dynamics, D r is the intrinsic rotary diffusivity of the bacterium andγ is the characteristic magnitude of the imposed velocity gradient. The solution of the kinetic equation is obtained numerically using a spectral Galerkin method, that yields the rheological properties (the shear viscosity, the first and second normal stress differences for simple shear, and the extensional viscosity for uniaxial extension) over the entire range of Pe. For simple shear, we find that the stress relaxation predicted by our analysis at small Pe is in good agreement with the experimental observations of Lopez et al. (2015). However, the analysis at large Pe yields relaxations that are qualitatively different. The rheological response in the experiments corresponds to a transition from a nearly isotropic suspension of active swimmers at small Pe, to an apparently (nearly) isotropic suspension of passive rods at large Pe. In contrast, the computations yield the expected transition to a nearly flow-aligned suspension of passive rigid rods at high Pe. We probe this active-passive transition systematically, complementing the numerical solution with analytical solutions obtained from perturbation expansions about appropriate base states. Our study suggests courses for future experimental and analytical studies that will help understand relaxation phenomena in active suspensions.

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“…The clearly non-monotonic curves reported here are different from the results reported previously by Saintillan and Shelley, 41 who did not observe any maximum at the transition density for neither the caracteristic length or time-scales, while the non-monotonic behaviour of τ(n) was previously observed by Krishnamurthy and Subramanian. 42 We attribute this difference to the significantly smaller system sizes used in earlier studies. We furthermore note that the predicted infinite-system critical density n c (Eq.…”

Section: Fluid Statisticsmentioning

confidence: 95%

Particle-resolved lattice Boltzmann simulations of 3-dimensional active turbulence

et al. 2019

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Collective behaviour in suspensions of microswimmers is often dominated by the impact of longranged hydrodynamic interactions. These phenomena include active turbulence, where suspensions of pusher bacteria at sufficient densities exhibit large-scale, chaotic flows. To study this collective phenomenon, we use large-scale (up to N = 3 × 10 6 ) particle-resolved lattice Boltzmann simulations of model microswimmers described by extended stresslets. Such system sizes enable us to obtain quantitative information about both the transition to active turbulence and characteristic features of the turbulent state itself. In the dilute limit, we test analytical predictions for a number of static and dynamic properties against our simulation results. For higher swimmer densities, where swimmer-swimmer interactions become significant, we numerically show that the length-and timescales of the turbulent flows increase steeply near the predicted finite-system transition density.Here, λ is the tumbling frequency by which individual swimmers randomise their swimming direction and κ is the stresslet magnitude, defined below. In order to probe the properties of J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-10 | 1 arXiv:1904.03069v2 [cond-mat.soft] 26 Aug 2019 J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-10 | 9

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Collective motion in a suspension of micro-swimmers that run-and-tumble and rotary diffuse

Cited by 37 publications

References 70 publications

Chemotactic behaviour ofEscherichia coliat high cell density

Chemotactic behaviour ofEscherichia coliat high cell density

Stress relaxation in a dilute bacterial suspension: the active–passive transition

Particle-resolved lattice Boltzmann simulations of 3-dimensional active turbulence

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