Escherichia coli swim on the right-hand side

Abstract

The motion of peritrichously flagellated bacteria close to surfaces is relevant to understanding the early stages of biofilm formation and of pathogenic infection. This motion differs from the random-walk trajectories of cells in free solution. Individual Escherichia coli cells swim in clockwise, circular trajectories near planar glass surfaces. On a semi-solid agar substrate, cells differentiate into an elongated, hyperflagellated phenotype and migrate cooperatively over the surface, a phenomenon called swarming. We have developed a technique for observing isolated E. coli swarmer cells moving on an agar substrate and confined in shallow, oxidized poly(dimethylsiloxane) (PDMS) microchannels. Here we show that cells in these microchannels preferentially 'drive on the right', swimming preferentially along the right wall of the microchannel (viewed from behind the moving cell, with the agar on the bottom). We propose that when cells are confined between two interfaces--one an agar gel and the second PDMS--they swim closer to the agar surface than to the PDMS surface (and for much longer periods of time), leading to the preferential movement on the right of the microchannel. Thus, the choice of materials guides the motion of cells in microchannels.

Cooperative self-propulsion of active and passive rotors

“…We limit our analysis to the case of rotors confined to a twodimensional plane with their spinning direction perpendicular to that plane. This constraint is often realized in experiments by confining rotors to a liquid/air interface [2][3][4][5] , or a thin layer of viscous fluid embedded in a different unbounded viscous fluid [25][26][27] , or in the case of many swimming unicellular organisms simply because they are attracted to a boundary that in turn triggers the rotational dynamics 8,9,[13][14][15][16] .…”

“…We will refer to the first class of rotors driven by external torques as passive rotors, while the name of active rotors will be reserved to those that are internally driven. Several examples of active rotors are found in the living world, including sperm cells [8][9][10][11][12] , bacteria [13][14][15][16] and algae 17 near a solid surface. Various artificial swimmers, inspired by their living counterparts, have also been engineered over the past decade, and provide realizations of active rotors [18][19][20][21] .…”

Microfluidics for bacterial chemotaxis

“…Because of their rapid generation times and the simplicity of their manipulation, microbial systems have been used to study a wide range of ecological processes [192][193][194][195][196]. On the other hand, the scale of microfluidic devices is ideal for application to microbial ecology, and a range of microbial processes has been successfully studied with microfluidics, including quorum sensing [197], chemotaxis [14,70,89], collective dynamics [198], and motility in confined environments [121,199]. Also, spatially structured microfluidic landscapes have recently been applied to the study of metapopulations of single [200] and competing bacterial species [201], and to demonstrate that microscale spatial structure enables coexistence [202].…”

Ferromagnetic Microswimmers

“…The swimmer's speed also depends on other external parameters such as the driving frequency f and the viscosity of the environment (data not shown), which provides flexibility in controlling the swimming behavior. Compared with the average velocities produced by micron-sized organisms such as E. coli ( 30 m s ÿ1 [20,23]), the speed of the dipole pair can be up to an order of magnitude higher (see Fig. 4, right-hand axis).…”