Abstract
Understanding how bacteria move close to a surface under various stimuli is crucial for a broad range of microbial processes including biofilm formation, bacterial transport and migration. While prior studies focus on interactions between single stimulus and bacterial suspension, we emphasize on compounding effects of flow shear and solid surfaces on bacterial motility, especially reorientation and tumble. We have applied microfluidics and digital holographic microscopy to capture a large number (>105) of 3D Escherichia coli trajectories near a surface under various flow shear. We find that near-surface flow shear promotes cell reorientation and mitigates the tumble suppression and re-orientation confinement found in a quiescent flow, and consequently enhances surface normal bacterial dispersion. Conditional sampling suggests that two complimentary hydrodynamic mechanisms, Jeffrey Orbit and shear-induced flagella unbundling, are responsible for the enhancement in bacterial tumble motility. These findings imply that flow shear may mitigate cell trapping and prevent biofilm initiation.
Highlights
Develop this concept that this shear-induced trapping mechanism would enhance cell-surface collision and lead to the higher rate of surface attachment
Using the system composed of E. coli and a solid surface under shear flows, we have demonstrated that subtle interplay of hydrodynamic forces on flagella in the presence of a solid surface and flow shear could significantly alter motility and subsequently change the dispersion characteristics of bacteria suspension near a surface
We demonstrated extensively that contrary to the case in Ref. 15, the flow shear can alleviates the suppression of tumbles and promotes angular dispersion near a solid surface, and subsequently reduces cell concentration as well as lowers the probability of cell attachment
Summary
Develop this concept that this shear-induced trapping mechanism would enhance cell-surface collision and lead to the higher rate of surface attachment. The supporting observations are reported by[20] This inconsistency highlights the current lack of understanding of the effects of flow shear on the near-surface bacterial motility, especially the motility relevant to cell orientation. We applied DHM and microfluidics[15,33] to study the effects of flow shear on the motility of wild-type E. coli (AW405) when it swims near a solid surface. We have succeeded in using DHM to simultaneously image up to ~8000 wild-type E. coli bacteria over the entire 200 μm depth of a microfluidic device, with a spatial resolution of 0.2 μm (lateral) and 0.5 μm (axial). By enabling simultaneous tracking of a large number of cells without any moving parts in the setup, this approach establishes DHM as a powerful technique for studying the motility change in the presence of environmental stimuli
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