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> Engineer turns bacteria into living
computers
In a step toward making living cells
function as if they were tiny computers,
engineers at Princeton have programmed bacteria
to communicate with each other and produce
color-coded patterns.
i-Newswire, 2005-04-29 -
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."
Contact: Eric
Quinones quinones@princeton.edu 609-258-5748 Princeton
University http://www.princeton.edu
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