List of movies and brief descriptions
Movie 1: This is a movie of E. coli on the surface of the PDMS wall. Flow is from the
top to the bottom of the field of view. The bacteria can be observed to swim towards their
left as they get dragged downstream. Some of the cells lose their stable direction (the
nose pointing to the left and upstream) occasionally (due to Brownian wobble and
miniature surface imperfections), but quickly reestablish their leftward swimming
pattern. The channel is 150 microns wide and about 93 μm deep. The volumetric flow
rate through the channel is 0.9 μl/min. The movie is in real-time, with 30 frames per
second (fps).
Movie 2: Here the cells are observed on the glass surface of the microchannel. When
viewed from the bottom and through the glass, the image appears inverted, though the
cells are still swimming towards their left. Upstream swimming along the left sidewall
and the crevice under it (along the right-hand-side of the images) is predominant. Some
upstream swimmers are also observed along the other side, as well. This movie is taken at
the same position along the channel of Movie 1, except the objective is focused at the
bottom (glass) surface of the microchannel. The volumetric flow rate through the channel
is 0.9 μl/min. The movie is in real-time, with 30 fps.
Movie 3: Upstream swimming takes place even at quite high flow rates. Here, the images
are from the same position and channel as in Movie 2, except that the volumetric flow
rate is now 3 μl/min. The movie is in real-time, with 30 fps.
Movie 4: This movie tracks an individual bacterium entering the left crevice (right side
of the images) along the glass surface, get bumped by another cell to orient downstream,
swim for a short period and then get reoriented upstream. Occasionally, downstream
swimmers like this cell may be observed along a side crevice, though they eventually get
reoriented upstream due to hydrodynamic forces. This movie is in real-time, with 30 fps.
Movie 5: Two strong swimmers executing the motions described in Figure 4-b (i,ii),
while the rest of the population is swimming towards the left (as in Figure 4-c (i)). The
movie is at half speed, with 15 fps.