Researchers have reported new information about how certain bacteria propel
themselves from one place to another. Insight into bacterial micro-movement
will benefit scientists and engineers developing nano-scale mechanical devices
that may one day push fluids and transport molecules without the aid of pumps
or electrical charges.
The findings, published in the June 30 issue of
the journal, Nature, may also help elucidate how
pathogens traverse the human body when causing disease.
Using a novel system of microscopic channels, Harvard
University researchers separated individual Escherichia
coli cells from their typical "swarm" and videotaped
them as they swam over different types of surfaces.
A laboratory workhorse and common gastrointestinal
bacterium, E. coli , preferred to swim near a gel-like
porous surface with characteristics similar to biological
tissues rather than near a glassy, solid one. In
fact, they swam next to the porous surface for much
longer periods of time.
First author Willow DiLuzio said, "Now that we've
established the bacterium's preference to swim toward
a specific kind of surface, we hope to harness this
basic information and focus on how to use it to direct
movement in microfluidic, cell-based bioassays and
sensors."
The team developed a new technique to fabricate
microchannels only 10 microns wide, or one-tenth
the width of an average human hair. The walls of
the channels were either a porous agar or a solid,
commercially available silicone-rubber compound.
E. coli use long, whip-like structures called flagella
to propel themselves. Motors in the cell's wall spin
the flagella into bundles that rotate counter-clockwise,
creating a twist that causes the bacterium to rotate
clockwise, or towards the right when viewed from
above.
If cells were introduced to each end of the channel
containing agar on the bottom, the cells preferentially
swam on the right-hand side of the microchannel resulting
in an ordered movement that resembled cars driving
on a two-way street. And the microbes swimming closer
to the agar surface moved faster than those swimming
near the solid surface.
The authors propose that the bacteria closer to
the porous surface experience less resistance and
thus move faster.
"Because of E. coli' s size, relative to the spacing
of surrounding water molecules, it's analogous to
a human trying to move through thick honey," said
DiLuzio. "Now, an entirely new set of hydrodynamic
properties have to be considered in order to understand
their movement as well as replicate it in man-made
nano-devices."
The surfaces of cells in the human body are often
coated with a layer similar to agar. Future research
into microbial movement will also be helpful in understanding
how human infectious diseases develop and how infection
might be halted in the body.
DiLuzio is supported by the National Science Foundation's
Education Human Resources directorate through an
award made to Harvard's Integrated Training Program
in Biomechanics.
-NSF-
Media Contacts
Richard (Randy) Vines, NSF (703) 292-7963 rvines@nsf.gov
Principal Investigators
George Whitesides, Harvard University (617) 495-9430 gwhitesides@gmwgroup.harvard.edu
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