Accumulation of swimming bacteria near a solid surface

Li, Guanglai; Bensson, James; Nisimova, Liana; Munger, Daniel; Mahautmr, Panrapee; Tang, Jay X.; Maxey, Martin; Brun, Yves V.

doi:10.1103/physreve.84.041932

Cited by 114 publications

(131 citation statements)

References 27 publications

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“…For suspensions in a bounded domain, the swimming cells accumulate near the surface, as observed for bacteria (Li et al 2011) and up-swimming, bottom-heavy algae (Pedley & Kessler 1992), two different cellular organisms with opposite swimming modes, one 'pushing' the other 'pulling'. Several experimental and theoretical studies of swimming particle interactions with surfaces show that the particle interaction with the wall can vary with particle size, swimming type and particle shape and the long time trajectory of a swimming particle moving near a surface is not easily predicted (Li et al 2011;Berke et al 2008;Spagnolie & Lauga 2012;Zhu, Lauga & Brandt 2013). While most of these studies were conducted for solid walls, the motion toward a stress free surface, such as an air and water interface, show some similarities.…”

Section: Introductionmentioning

confidence: 99%

Active suspensions in thin films: nutrient uptake and swimmer motion

et al. 2013

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A numerical study of swimming particle motion and nutrient transport is conducted for a semidilute to dense suspension in a thin film. The steady squirmer model is used to represent the motion of living cells in suspension with the nutrient uptake by swimming particles modelled using a first-order kinetic equation representing the absorption process that occurs locally at the particle surface. An analysis of the dynamics of the neutral squirmers inside the film shows that the vertical motion is reduced significantly. The mean nutrient uptake for both isolated and populations of swimmers decreases for increasing swimming speeds when nutrient advection becomes relevant as less time is left for the nutrient to diffuse to the surface. This finding is in contrast to the case where the uptake is modelled by imposing a constant nutrient concentration at the cell surface and the mass flux results to be an increasing monotonic function of the swimming speed. In comparison to non-motile particles, the cell motion has a negligible influence on nutrient uptake at lower particle absorption rates since the process is rate limited. At higher absorption rates, the swimming motion results in a large increase in the nutrient uptake that is attributed to the movement of particles and increased mixing in the fluid. As the volume fraction of swimming particles increases, the squirmers consume slightly less nutrients and require more power for the same swimming motion. Despite this increase in energy consumption, the results clearly demonstrate that the gain in nutrient uptake make swimming a winning strategy for micro-organism survival also in relatively dense suspensions.

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Section: Introductionmentioning

confidence: 99%

Active suspensions in thin films: nutrient uptake and swimmer motion

et al. 2013

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“…In particular, it did not require the presence of a nearby surface as evidenced by the uniform bacterial distribution in the absence of flow, in contrast to the known accumulation of motile cells arising from hydrodynamic 6 or short-range steric 7,8 interactions with boundaries.…”

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Bacterial transport suppressed by fluid shear

2014

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Bacteria often live in dynamic fluid environments 1-3 and flow can a ect fundamental microbial processes such as nutrient uptake 1,4 and infection 5 . However, little is known about the consequences of the forces and torques associated with fluid flow on bacteria. Through microfluidic experiments, we show that fluid shear produces strong spatial heterogeneity in suspensions of motile bacteria, characterized by up to 70% cell depletion from low-shear regions due to 'trapping' in high-shear regions. Two mathematical models and a scaling analysis accurately capture these observations, including the maximal depletion at mean shear rates of 2.5-10 s −1 , and reveal that trapping by shear originates from the competition between the cell alignment with the flow and the stochasticity in the swimming orientation. We show that this shear-induced trapping directly impacts widespread bacterial behaviours, by hampering chemotaxis and promoting surface attachment. These results suggest that the hydrodynamic environment may directly a ect bacterial fitness and should be carefully considered in the study of microbial processes.We investigated the effect of flow on motile bacteria by tracking them in precisely controlled laminar flows generated in a microfluidic channel (Fig. 1a). To ensure that the dominant velocity gradients occurred in the horizontal observation plane, at the channel mid-depth, we used a microchannel with aspect ratio H /W > 1 (height H = 750 µm; width W = 425 µm). In that plane, the velocity profile, u(y) = U [1 − 4(y/W ) 2 ], where U is the flow velocity at the channel centreline, is parabolic, and, thus, the shear rate S(y) = du/dy = −8yU /W 2 varies linearly with distance y across the channel and is zero at the centreline (Fig. 1b). In this flow, smooth-swimming Bacillus subtilis bacteria swam unperturbed in straight paths (Fig. 1c) when near the centre of the channel, where the local shear rate was small. Conversely, in high-shear-rate regions, trajectories exhibited frequent loops resulting from rotation of the swimming bacteria by the hydrodynamic torque imparted by the local shear (Fig. 1d). The opposite handedness of the loops on either side of the channel centreline reflects the opposite sign of the shear rate (Fig. 1c,d and Supplementary Movie 1). As shown below, these looping trajectories resulted in bacteria becoming trapped in the high-shear region of the channel.At the population scale, this trapping effect resulted in a marked depletion of cells from the central, low-shear region of the flow, and consequently, in an accumulation in the flanking regions of higher shear. When the flow was impulsively started from rest, the initially uniform distribution of cells over the imaging region across the channel width (Fig. 1e) rapidly (5-10 s) evolved into a distribution characterized by considerably fewer cells in the central part of the channel (Fig. 1f-h). The magnitude of the depletion was severe, with local cell concentrations dropping by 70% (Fig. 1h). The absence of depletion in control experime...

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“…The second mechanism involves hydrodynamic torques that arise in anisotropic bodies swimming in close contact with the wall and leading to swimming at a finite angle with the wall surface [22]. More recently, the role of hydrodynamic interactions has been questioned [24,25], suggesting that steric repulsion and rotational Brownian motion are enough to reproduce the observed accumulation of bacteria in the proximity of solid walls. Despite the extensive theoretical and numerous experimental works on the hydrodynamics of bacterial swimming, a straightforward, unambiguous, and direct identification of a main mechanism responsible for wall entrapment is still lacking.…”

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Hydrodynamic Trapping of Swimming Bacteria by Convex Walls

et al. 2015

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Swimming bacteria display a remarkable tendency to move along flat surfaces for prolonged times. This behavior may have a biological importance but can also be exploited by using microfabricated structures to manipulate bacteria. The main physical mechanism behind the surface entrapment of swimming bacteria is, however, still an open question. By studying the swimming motion of Escherichia coli cells near microfabricated pillars of variable size, we show that cell entrapment is also present for convex walls of sufficiently low curvature. Entrapment is, however, markedly reduced below a characteristic radius. Using a simple hydrodynamic model, we predict that trapped cells swim at a finite angle with the wall and a precise relation exists between the swimming angle at a flat wall and the critical radius of curvature for entrapment. Both predictions are quantitatively verified by experimental data. Our results demonstrate that the main mechanism for wall entrapment is hydrodynamic in nature and show the possibility of inhibiting cell adhesion, and thus biofilm formation, using convex features of appropriate curvature. DOI: 10.1103/PhysRevLett.114.258104 PACS numbers: 47.63.Gd, 87.17.Jj, 87.18.Ed Self-propelled bacteria living in aqueous media have constant, vivid interactions with their local environment, which may dramatically alter their swimming behavior [1][2][3][4][5][6][7][8]. Often, bacterial habitats are physically confined by solid boundaries. Physical interactions with these solid surfaces give rise to a rich variety of dynamical phenomena like steering or rectification of swimming direction [9] and the propulsion of microfabricated structures [10]. Understanding the physical mechanisms behind cell-surface interactions is of crucial importance to design structures that could fully exploit those effects for microfluidic applications. On the other hand, a quantitative understanding of wall entrapment and subsequent adhesion would allow us to design surfaces that hinder unwanted biological processes like biofilm formation. Surface colonization by biofilm-forming bacteria is initiated by cell contact and adhesion to the surface [11][12][13]. The subsequent biofilm growth can cause highly resistant bacterial infections on medical implants and catheters or impaired industrial equipment [14][15][16][17][18][19].Using a tracking microscope, Frymier et al. observed that bacteria display a marked tendency to swim adjacent to wall surfaces [20]. At the beginning, this behavior was attributed to an attractive interaction potential between the cell body and the solid surface. It was later proposed, however, that, while DLVO forces could be responsible for irreversible adhesion, wall entrapment during swimming may have a purely hydrodynamic origin [21,22]. Hydrodynamic effects can indeed give rise to wall entrapment via two distinct mechanisms. The first one is via farfield, dipolar flows that, once reflected by a flat wall, give rise to reorientation parallel to the wall surface as well as an attraction by the wa...

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Accumulation of swimming bacteria near a solid surface

Cited by 114 publications

References 27 publications

Active suspensions in thin films: nutrient uptake and swimmer motion

Active suspensions in thin films: nutrient uptake and swimmer motion

Bacterial transport suppressed by fluid shear

Hydrodynamic Trapping of Swimming Bacteria by Convex Walls

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