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Synthetic Biologists Design ‘Living
Materials’ That Build Themselves
film and latched on to gold nanoparticles
that the researchers had sprinkled into their
beakers, creating a network that conducts
electricity (see figure, below).
By growing both batches of E. coli
together, Lu’s team could vary the
composition of the film just by adding AHL
and aTc at different times. In this case,
the varying composition didn’t add new
function. But it sets the stage for doing so
by binding other materials, for example. In
a separate experiment, they used different
peptide tags and chemical triggers to create
bacteria that could trap tiny semiconductor
particles called quantum dots, which altered
the optical properties of the biofilm.
Lu now hopes to take advantage of recent
advances in synthetic biology, in which
researchers have programmed bacteria to
Organisms are master builders. Crabs aren’t alive. That means, for example, that
assemble shells, corals amass reefs, and our they can’t respond to their environment the
own tissues build bone. Now, synthetic biol- way bacteria can: by organizing themselves
ogists are taking control of the construction in groups or healing themselves.
process. Researchers in Massachusetts
The new work, from Timothy Lu, a
reported this week in Nature Materials that synthetic biologist at MIT, and colleagues,
they’ve reprogrammed the genetic circuitry brings these previously disparate fields
of bacteria to construct electronic and opti- together. “Our idea is to put the living and
cal materials, complete with living cells in nonliving worlds together to make hybrid
their midst.
materials that have living cells in them and
The new materials can’t yet compete are functional,” Lu says. They started with
with conventional electronic devices. Escherichia coli bacteria that naturally
Nevertheless, outside researchers say the feat cooperate to produce sheetlike biofilms atop
opens a new door to using
genetically engineered
Nonconductive
organisms to assemble
biofilm
complex materials from the
ground up, with minimal
No aTc
help. “It’s fantastic work,”
says Lingchong You,
Engineered
bacteria
a biomedical engineer
Electrode
at Duke University in
to measure
Durham, North Carolina,
conductivityy
who was not involved in
Conductive
His-tagged curli fibers
the research. Traditional
biofilm
manufacturing is typically
Gold
nanoparticles
energy-intensive, polluting,
aTc
and often hazardous for
workers. “But if we can
harness the power of
cells [to build structures],
we can make the entire
process ‘green,’ ” You says. Filmmaker. When exposed to a chemical called aTc, bacteria produce fibers (pink) that cause them to attach to a surface and to one
Moreover, because organ- another. Amino acids called histidines on the fibers then grab gold nanoparticles, forming an electrically conducting film.
isms are adept at engineering materials at many different size different surfaces. The bacteria bind these form colonies in the form of rings, bars, and
scales—the way our bodies imprint bone films together by secreting proteins called other shapes. That could lay the groundwork
with structure on the nanoscale, microscale, curli fibers. Made up of repeated protein for more complex architectures that could
and meter scale—the new work holds the subunits called CsgA, the fibers glue the serve as electrodes, environmental sensors,
potential for adding new levels of complexity bacteria to surfaces and to one another.
and artificial tissues. Ultimately, the living
to engineered materials.
For their experiments, Lu’s team first materials might be fashioned into devices
The new work isn’t the first foray into disabled the genetic pathway that allows that repair themselves when damaged.
marrying engineered organisms with bacterial cells to produce CsgA. They
The technique might also be used to
materials. In 1999, for example, Angela replaced it with an engineered genetic sponge up environmental toxins such as
Belcher, a chemist now at the Massachusetts circuit that produces CsgA only when cadmium and recycle the material into
Institute of Technology (MIT) in Cambridge, the researchers add a chemical trigger, complex optical and organic devices. It may
and her colleagues engineered viruses to a molecule called AHL. The team then even prove useful in prospecting: Designer
assemble semiconductor nanoparticles on engineered a separate batch of E. coli to bacteria, for example, might harvest gold
their surfaces. Belcher’s group has since produce altered CsgA tagged with short from their environment and concentrate it in
gone on to program viruses to construct protein strands, or peptides, containing mats that could be scooped up. Such tests
everything from electrodes for lithium- multiple histidine amino acids, which bind remain a ways off, however. Regulators
ion batteries and photovoltaics to catalysts metal particles. These bacteria expressed the would need to be convinced that engineered
that split water to generate hydrogen fuel. histidine-tagged CsgAs only in response to bacteria don’t pose risks when released into
But because viruses don’t harbor their own another chemical trigger, called aTc. When the environment.
cellular machinery, the materials they make aTc was present, the bacteria settled into a
–ROBERT F. SERVICE
www.sciencemag.org
SCIENCE
VOL 343
Published by AAAS
28 MARCH 2014
1421
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