This movie shows iontophoretic stimulation of tethered E. coli. When the time display goes white, the pipette ejects α-methylaspartate, a nonmetabolizable attractant. After a delay averaging 0.2 s, the cell changes its direction of rotation from CW to CCW. See Segall, J.E., Manson, M.D. and Berg, H.C. Signal processing times in bacterial chemotaxis. Nature 296, 855-857 (1982).
Movement of 0.8 µm dia. latex spheres in water at room temperature.
Tethered cells are pushed forward or backward by a high-frequency (2.25 MHz) rotating electric field. The first scene shows 2 of the 4 electrodes, and the remaining scenes the fate of a tethered cell. When pushed backward the motor driving the cell broke catastrophically. The video camera, running at 60 Hz, was shuttered, so spinning cells look like daisies, and if spinning an even multiple of 60 Hz, they appear stationary. See Berg, H.C. and Turner, L. Torque generated by the flagellar motor of Escherichia coli. Biophys. J. 65, 2201-2216 (1993).
Cells of E. coli were examined by video-enhanced differential-interference-contrast microscopy. The depth of field is shallow, and all the cells are near the bottom of the preparation. Some cells are shown de-energized, exhibiting filaments with a variety of wave forms: normal, coiled, semi-coiled, curly 1, and curly 2. See Block, S.M., Fahrner, K.A. and Berg, H.C. Visualization of bacterial flagella by video-enhanced light microscopy. J. Bacteriol. 173, 933-936 (1991).
The spots on these cells are GFP-FliG. For related work, where the figures are in color, see Sourjik, V. and Berg, H.C. Location of components of the chemotaxis machinery of Escherichia coli using fluorescent-protein fusions. Molec. Microbiol. 37, 740-751 (2000).
A swimming E. coli cell is trapped by optical tweezers and moved in the x,y-plane and then in the z-direction and finally released. See Block, S.M., Blair, D.F. and Berg, H.C. Compliance of bacterial flagella measured with optical tweezers. Nature 338, 514-517 (1989).
Rotation of a tethered E. coli cell is blocked by a latex bead held in an optical trap. The stage is gyrated at a series of different speeds so that the cell can rotate (either forward or backward). The displacement of the bead in the trap, visible as a wobble, provides a measure of the force exerted on the bead. Other cells in the field are seen to gyrate, if stuck to the glass, or to spin, if tethered. See Berry, R.M. and Berg, H.C. Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers. Proc. Natl. Acad. Sci. USA 94, 14433-14437 (1997).
This spiral organism has a flagellar bundle at either end and swims in the direction of its long axis. Cells are typically 50 µm long. They require some long-range communication system (membrane potential?), because when the cells back up, their flagellar bundles change direction synchronously. S. volutans was first seen by van Leeuwenhoek in 1676.
This dye can crystallize out in the cytoplasm of E. coli and provide a marker for different ends of a cell, a marker readily visible by dark-field microscopy. This movie shows labeled cells swimming smoothly. However, when cells tumble, either end can go forward. Therefore, E. coli does not have a nose. See Berg, H.C. and Turner, L. Cells of Escherichia coli swim either end forward. Proc. Natl. Acad. Sci. USA 92, 477-479 (1995).
If you pour a thin stream of a viscous fluid (like honey) from a pot onto a plate, it tends to coil up. See Mahadevan, L., Ryu, W.S. and Samuel, A.D.T. Fluid 'rope tricke' investigated. Nature 392, 140 (1998).