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Bacterial Sensors
Engineered
E. coli bacteria signal environmental changes
Results: Princeton University and
Caltech researchers have genetically engineered E. coli
bacteria to give off red or green fluorescent light in
response to different concentrations of a cell-signaling
molecule secreted by a third type of E. coli. Incubating
the three types of E. coli in petri dishes resulted in
controllable patterns. In one experiment, the
researchers produced concentric circles of different
colors, with the signaling cells in the center.
Surrounding them were two types of fluorescing cells:
one that emitted green light when sensing a high
concentration of the signaling molecule, and another
that gave off red light at medium concentrations.
Why it Matters: Researchers had
previously programmed cells to communicate individually
or in small groups. Here the Princeton and Caltech team
engineered larger populations of bacteria to work
together to form visible patterns that could be used,
for example, to signal the presence of a toxic chemical.
Because the bacteria produce different signals in
response to concentrations of a target chemical, they
could flag areas of high concentration as likely sources
of wider contamination. In theory, bacteria-based
sensors could be more sensitive to a broader range of
chemicals than conventional sensors are.
Methods: The researchers, led by Ron
Weiss and Frances Arnold, used mathematical models of
gene activity to predict the responses of different
strains of E. coli to distinct ranges of
signaling-molecule concentrations. The researchers then
synthesized the strains likely to be most useful by
inserting into the E. coli genome desired genes, such as
those that code for fluorescent proteins. They then
spread a mixture of these strains in petri dishes
containing growth media and incubated them overnight.
Using a fluorescence microscope, they took pictures of
the plates to reveal the different colored patterns.
Next Step: To turn microorganisms
into sensors, the researchers must couple their gene
networks to receptors that specifically bind to target
chemicals. They will also need to design the sensors so
that the cells remain alive and stable even outdoors.
And they will likely need to devise some kind of control
switch to reset or turn off the sensors.
Source: Basu, S., et al. 2005. A synthetic
multicellular system for programmed pattern formation.
Nature 434:1130-4. |