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Engineer turns bacteria into living computers |
| Theallineed.com /
NC&T/PU |
The feat, accomplished in a biology
lab within the Department of Electrical Engineering, represents an
important proof-of-principle in an emerging field known as
"synthetic biology," which aims to harness living cells as
workhorses that detect hazards, build structures or repair tissues
and organs within the body.
"We are really moving beyond the ability
to program individual cells to programming a large collection --
millions or billions -- of cells to do interesting things," said Ron
Weiss, an assistant professor of electrical engineering and
molecular biology.
Collaborating with researchers at the
California Institute of Technology, Weiss and graduate student
Subhayu Basu programmed E. coli bacteria to emit red or green
fluorescent light in response to a signal emitted from another set
of E. coli. In one experiment, the cells glowed green when they
sensed a higher concentration of the signal chemical and red when
they sensed a lower concentration. In a Petri dish, they formed a
bull's-eye pattern -- a green circle inside a red one -- surrounding
the sender cells.
In addition to demonstrating that the
genetic programming techniques work, this sensing system could be
useful for the detection of chemicals or organisms in laboratory
tests. "The bull's-eye could tell you: This is where the anthrax
is," said Weiss.
The researchers published their results in
the April 28 issue of Nature. In addition to Weiss and Basu, authors
of the paper are postdoctoral researcher Yoram Gerchman at Princeton
and professor of chemical engineering Frances Arnold and graduate
student Cynthia Collins at Caltech. It was funded by a grant from
the U.S. Defense Advanced Research Projects Agency.
In
previous work, including a paper published March 8 in the
Proceedings of the National Academy of Sciences along with Sara
Hooshangi and Stephan Thiberge, Weiss showed the feasibility of
inserting engineered pieces of DNA into cells to make them behave in
the same manner as digital circuits. The cells, for example, could
be made to perform basic mathematical logic and produce crisp,
reliable readouts that are more commonly associated with silicon
chips than biological organisms. The new paper applies similar
techniques to a large population of cells.
"Here we're
showing an integrated package where the cells have an ability to
send messages and other cells have the ability to act on these
messages," said Weiss.
The creation of patterns, such as the
bull's-eye effect, is a key step in one of Weiss' eventual goals,
which is to have the cells secrete materials that build physical
devices such as antennas or transmitters in places that are hard for
humans to reach. Programmed cells also could be used to control the
repair or construction of tissues within the body, possibly guiding
stem cells to the locations where they are needed for the growth of
new nerve or bone cells in a process Weiss called "programmed tissue
engineering."
Even the early step of creating patterns in a
Petri dish, however, may be useful as a tool for other scientists,
particularly developmental biologists who are trying to understand
how the cells of an embryo arrange themselves into patterns that
become the various body parts of a mature organism. In fruit fly
embryos, for example, the first cells are thought to differentiate
into the head, abdomen and other parts based on the concentration of
chemical signals that are emitted from the ends of the
embryo.
In addition to conducting laboratory experiments,
Weiss and colleagues are creating computer models of their
engineered systems, which allow them to study how small
modifications would affect the ultimate behavior of the organisms.
So far, said Weiss, the experimental results have matched the
computer models fairly closely, but the goal is to have a
mathematically exact description of how each component
works.
"One of the nice things about synthetic biology is
that because we built the network from scratch, we should be able to
model all the important details," he said. At some point in the
future, he said, scientists will be able to choose a behavior they
want from cells, and a computer program will create a genetic
circuit to accomplish the task. "Then we can do an experiment to see
if the community of cells is behaving as we desire. That is going to
have a tremendous number of applications." |
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