Oscillatory surface rheotaxis of swimming E. coli bacteria

Abstract

Bacterial contamination of biological channels, catheters or water resources is a major threat to public health, which can be amplified by the ability of bacteria to swim upstream. The mechanisms of this ‘rheotaxis’, the reorientation with respect to flow gradients, are still poorly understood. Here, we follow individual E. coli bacteria swimming at surfaces under shear flow using 3D Lagrangian tracking and fluorescent flagellar labelling. Three transitions are identified with increasing shear rate: Above a first critical shear rate, bacteria shift to swimming upstream. After a second threshold, we report the discovery of an oscillatory rheotaxis. Beyond a third transition, we further observe coexistence of rheotaxis along the positive and negative vorticity directions. A theoretical analysis explains these rheotaxis regimes and predicts the corresponding critical shear rates. Our results shed light on bacterial transport and reveal strategies for contamination prevention, rheotactic cell sorting, and microswimmer navigation in complex flow environments.

Phytoplankton Orientation in a Turbulent Ocean: A Microscale Perspective

“…Studies on microorganism motility under distinct flow conditions further evidence how coupling between swimming and fluid flow can result in non-random cell orientations, and consequently, non-uniform cell accumulation. Paradigmatic examples include laboratory experiments and modeling on gyrotaxis, where local shear flow couples to motility to induce cell focusing in localized streams (Kessler, 1985;Pedley and Kessler, 1992), dynamic aggregation regimes and intense patchiness in turbulent flows far exceeding that of randomly distributed, non-motile populations (Durham et al, 2013); or rheotaxis, where swimming cells (whether bacteria, heterotrophs, sperm cells, or phytoplankton) reorient with respect to gradients in the flow velocity to successfully migrate in the local upstream direction (Marcos et al, 2012;Bukatin et al, 2015;Mathijssen et al, 2019).…”

Wall entrapment of peritrichous bacteria: a mesoscale hydrodynamics simulation study

“…Simulation studies with a single flagellum aligned with the cell body yield the inclination angle θ i ≈ 10 • . 70 The larger value could be a consequence of the particular geometry of the applied E. coli model, where the helix radius increases toward the rear end of the cell. Since the helix radius is larger than that of the cell, steric flagellum-surface interactions prevent parallel alignment with respect to the surface and imply an orientation toward the wall.…”

State diagram of a three-sphere microswimmer in a channel

“…This behavior has also been seen in an analogous system of self-phoretic active Janus particles [92][93][94][95][96][97][98][99][100] , where a complex phase diagram has been found, based on the initial orientation and the distance separating the swimmer from the wall. Additional investigations have considered the hydrodynamic interactions between two squirmers near a boundary 101 , the dynamics of active particles near a fluid interface [102][103][104] , swimming in a confining microchannel [105][106][107][108][109][110][111][112][113][114][115][116] , inside a spherical cavity [117][118][119] , near a curved obstacle 120,121 and in a liquid film [122][123][124] . Meanwhile, other studies have considered the low-Reynolds number locomotion in non-Newtonian fluids [125][126][127][128][129][130][131][132][133] where boundaries have been found to drastically alter the swimming trajectories of microswimmers.…”