RECRUITING BACTERIA : SELF HEALING MATERIALS
For most people biofilms conjure up images of
slippery stones in a streambed and dirty drains. While there are plenty of
"bad" biofilms around -- they even cause pesky dental plaque and a
host of other more serious medical problems -- a team at the Wyss Institute for
Biologically Inspired Engineering at Harvard University sees biofilms as a
robust new platform for designer nanomaterials that could clean up polluted
rivers, manufacture pharmaceutical products, fabricate new textiles, and more.
In
short, they want to give biofilms a facelift, and have developed a novel
protein engineering system called BIND to do so. Using BIND, which stands for
Biofilm-Integrated Nanofiber Display, the team said biofilms could be
tomorrow's living foundries for the large-scale production of biomaterials that
can be programmed to provide functions not possible with existing materials.
They have reported the proof-of-concept in Nature Communications .
"Most
biofilm-related research today focuses on how to get rid of biofilms, but we
demonstrate here that we can engineer these super tough natural materials to
perform specific functions -- so we may want them around in specific quantities
and for specific applications," said Wyss Institute Core Faculty member Neel
Joshi, Ph.D., the study's senior author. Joshi is also an Associate Professor
of Chemical and Biological Engineering at the Harvard School of Engineering and
Applied Sciences (SEAS).
Biofilms
also self-assemble and self-heal. "If they get damaged, they grow right
back because they are living tissues," said lead author Peter Nguyen,
Ph.D., a Postdoctoral Fellow at the Wyss Institute and Harvard SEAS.
Biofilms
are communities of bacteria ensconced in a slimy, but extremely tough, matrix
of extracellular material composed of sugars, proteins, genetic material and
more. During biofilm formation individual bacteria pump out proteins that
self-assemble outside the cell -- creating tangled networks of fibers that
essentially glue the cells together into communities that keep the bacteria
safer than they would be on their own.
Interest
in biofilm engineering is skyrocketing, and while several other teams have
recently developed genetic tools to control biofilm formation, Joshi's team
altered the composition of the extracellular material itself -- essentially
turning it into a self-replicating production platform to churn out whatever
material they wish to produce.
"Until
recently there was not enough cooperation between synthetic biologists and
biomaterials researchers to exploit the synthetic potential of biofilms this
way. We are trying to bridge that gap," Joshi said.
The
team genetically fused a protein with a particular desired function -- for
example, one known to adhere to steel -- onto a small protein called CsgA that
is already produced by E. coli bacteria. The appended domain then
went along for the ride through the natural process by which CsgA gets secreted
outside the cell, where it self-assembled into supertough proteins called
amyloid nanofibers. These amyloid proteins retained the functionality of the
added protein -- ensuring in this case that the biofilm adhered to steel.
Amyloid
proteins traditionally get a bad rap for their role in causing tremendous
health challenges such as Alzheimer's disease, but in this case their role is
fundamental to making BIND so robust. These amyloids can spontaneously assemble
into fibers that, by weight, are stronger than steel and stiffer than silk.
"We
are excited about the versatility of the method, too," Joshi said. The
team demonstrated an ability to fuse 12 different proteins to the CsgA protein,
with widely varying sequences and lengths. This means in principle that they
can use this technology to display virtually any protein sequence -- a
significant feature because proteins perform an array of impressive functions
from binding to foreign particles to carrying out chemical reactions,
transmitting signals, providing structural support, and transporting or storing
certain molecules.
Not
only can these functions be programmed into the biofilm one at a time, but they
can be combined to create multifunctional biofilms as well.
The
concept of the microbial factory is not a new one, but for the first time it is
being applied to materials, as opposed to soluble molecules like drugs or
fuels. "We are essentially programming the cells to be fabrication
plants," Joshi said. "They don't just produce a raw material as a
building block, they orchestrate the assembly of those blocks into higher order
structures and maintain that structure over time."
"The
foundational work Neel and his team are doing with biofilms offers a glimpse
into a much more environmentally sustainable future where gargantuan factories
are reduced to the size of a cell that we can program to manufacture new materials
that meet our everyday needs -- from textiles to energy and environmental
clean-up," said Wyss Institute Founding Director Don Ingber, M.D., Ph.D.
For
now the team has demonstrated the ability to program E.
coli biofilms that
stick to certain substrates, such as steel, others that can immobilize an array
of proteins or promote the templating of silver for construction of nanowires.
Comments
Post a Comment