Carpets and microchannels
Cells of Serratia marcescens adhere to a nonpolar surface and propel the adjacent fluid. If the surface is of a polystyrene latex bead or a small chip of a sheet of PDMS, the cells propel the bead or the chip. Isolated cells of E. coli move over a surface in right-hand spirals (when viewed from above the surface). When constrained by a microchannel over agar, the cells prefer to swim next to the agar.
Movies, bacterial carpets.
Movies, cells in microchannels.
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DiLuzio, W.R., Turner, L., Mayer, M., Garstecki, P., Weibel, D.B., Berg, H.C. and Whitesides, G.M. Escherichia coli swim on the right-hand side. Nature 435, 1271-1274 (2005).
Hulme, S.E., DiLuzio, W.R., Shevkoplyas, S.S., Turner, L., Mayer, M., Berg, H.C., and Whitesides, G.M. Using ratchets and sorters to fractionate motile cells of Escherichia coli by length. Lab on a Chip 8, 1888-1895 (2008).