Fluctuations and Rheology in Active Bacterial Suspensions

Chen, Daniel T. N.; Lau, Andy C.W.; Hough, Loren E.; Islam, Mohammad F.; Goulian, Mark; Lubensky, T. C.; Yodh, Arjun G.

doi:10.1103/physrevlett.99.148302

Cited by 135 publications

(123 citation statements)

References 28 publications

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“…Typically, the concentration of swimming bacteria embodied a 10% area fraction of the interface -large enough to lead to collective motion such as swirling, which influenced colloidal motion. A substantial literature has addressed the mobility of colloidal probes in the presence of motile bacteria and other microbial swimmers both in bulk (3D) and in quasi-two-dimensional contexts [3,[53][54][55][56][57][58][59][60][61]. One motivation for studying the colloidal dynamics in suspensions of swimming microbes is their utility as model systems for investigating the non-equilibrium statistical mechanics of active complex fluids.…”

Section: A Particle Trackingmentioning

confidence: 99%

Films of bacteria at interfaces: three stages of behaviour

et al. 2015

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Bacterial attachment to a fluid interface can lead to the formation of a film with physicochemical properties that evolve with time. We study the time evolution of interface (micro)mechanics for interfaces between oil and bacterial suspensions by following the motion of colloidal probes trapped by capillarity to determine the interface microrheology. Initially, active bacteria at and near the interface drive superdiffusive motion of the colloidal probes. Over timescales of minutes, the bacteria form a viscoelastic film which we discuss as a quasi-two-dimensional, active, glassy system. To study late stage mechanics of the film, we use pendant drop elastometry. The films, grown over tens of hours on oil drops, are expanded and compressed by changing the drop volume. For small strains, by modeling the films as 2D Hookean solids, we estimate the film elastic moduli, finding values similar to those reported in the literature for the bacteria themselves. For large strains, the films are highly hysteretic. Finally, from wrinkles formed on highly compressed drops, we estimate film bending energies. The dramatic restructuring of the interface by such robust films has broad implications, e.g. in the study of active colloids, in understanding the community dynamics of bacteria, and in applied settings including bioremediation.

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Section: A Particle Trackingmentioning

confidence: 99%

Films of bacteria at interfaces: three stages of behaviour

et al. 2015

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“…At long times, particles exhibit enhanced diffusivities D eff greater than D 0 , their thermal (Brownian) diffusivity [17][18][19][20][25][26][27] . These traits are a signature of the nonequilibrium nature of active fluids; the deviation from equilibrium also manifests in violations of the fluctuation dissipation theorem 28 .…”

Section: Introductionmentioning

confidence: 99%

Particle diffusion in active fluids is non-monotonic in size

et al. 2016

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We experimentally investigate the effect of particle size on the motion of passive polystyrene spheres in suspensions of Escherichia coli. Using particles covering a range of sizes from 0.6 to 39 microns, we probe particle dynamics at both short and long time scales. In all cases, the particles exhibit super-diffusive ballistic behavior at short times before eventually transitioning to diffusive behavior. Surprisingly, we find a regime in which larger particles can diffuse faster than smaller particles: the particle long-time effective diffusivity exhibits a peak in particle size, which is a deviation from classical thermal diffusion. We also find that the active contribution to particle diffusion is controlled by a dimensionless parameter, the Péclet number. A minimal model qualitatively explains the existence of the effective diffusivity peak and its dependence on bacterial concentration. Our results have broad implications on characterizing active fluids using concepts drawn from classical thermodynamics.

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“…Beyond the study of single cells, anomalous fluctuations were also detected in active bacterial suspensions [11]. Here, the diffusion of tracer particles in low-density bacterial cultures was characterized in detail, in well defined and short periods of time.…”

Section: Introductionmentioning

confidence: 99%

Living bacteria rheology: Population growth, aggregation patterns, and collective behavior under different shear flows

et al. 2014

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The activity of growing living bacteria was investigated using real-time and in situ rheologyin stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus -strain COL and its isogenic cell wall autolysis mutant -were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the two strains follow different and rich behaviours, with no counterpart in the optical density or in the population's colony forming units measurements. While the viscosity of strain COL keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain decreases steeply, still in the exponential phase, remains constant for some time and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviours, which were observed to be shear stress dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL, obtained with oscillatory shear, exhibit power-law behaviours whose exponent are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant have complex behaviours, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. These behaviours reflect nevertheless the bacteria growth stage.

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Fluctuations and Rheology in Active Bacterial Suspensions

Cited by 135 publications

References 28 publications

Films of bacteria at interfaces: three stages of behaviour

Films of bacteria at interfaces: three stages of behaviour

Particle diffusion in active fluids is non-monotonic in size

Living bacteria rheology: Population growth, aggregation patterns, and collective behavior under different shear flows

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