Researchers at the University of Massachusetts Amherst have discovered a tiny biological structure that is highly electrically conductive. This breakthrough helps describe how microorganisms can clean up groundwater and produce electricity from renewable resources. It may also have applications in the emerging field of nanotechnology, which develops advanced materials and devices in extremely small dimensions.

Researchers at the University of Massachusetts
Amherst have discovered a tiny biological structure that is highly electrically
conductive. This breakthrough helps describe how microorganisms can clean
up groundwater and produce electricity from renewable resources. It may also
have applications in the emerging field of nanotechnology, which develops
advanced materials and devices in extremely small dimensions.


The findings of microbiologist Derek R. Lovley’s research
team are published in the June 23rd issue of Nature. Researchers
found that the conductive structures, known as “microbial nanowires,” are
produced by a novel microorganism known as Geobacter. The nanowires are incredibly
fine, only 3-5 nanometers in width, but quite durable and more than a thousand
times long as they are wide.

“Such long, thin conductive structures are unprecedented in biology,” said
Lovley. “This completely changes our concept of how microorganisms can handle
electrons, and it also seems likely that microbial nanowires could be useful
materials for the development of extremely small electronic devices.”

“The microbial world never stops surprising us,” said Dr. Aristides Patrinos
of the U.S. Department of Energy, which funds the Geobacter research. “The
remarkable and unexpected discovery of microbial structures comprising microbial
nanowires that may enable a microbial community in a contaminated waste
site to form mini-power grids could provide new approaches to using microbes
to assist in the remediation of DOE waste sites; to support the operation
of mini-environmental sensors, and to nano-manufacture in novel biological
ways. This discovery also illustrates the continuing relevance of the physical
sciences to today’s biological investigations.”

Eugene Madsen, a Cornell University research microbiologist, noted, “I have
watched and judged, in peer review, many of Dr. Lovley’s remarkable scientific
advancements since the discovery of Geobacter in 1987. The latest advancement,
microbial nanowires, is another major milestone because it may usher in a
new era of exploration of both microbial respiration and bio-electronics.”
The findings, he said, are “promising and exciting,” although he emphasized
the information must be independently confirmed and extended by other microbiologists
and biophysicists.

Geobacter are the subject of intense investigation because they are useful
agents in the bioremediation of groundwater contaminated with pollutants
such as toxic and radioactive metals or petroleum. They also have the ability
to convert human and animal wastes or renewable biomass into electricity.
To carry out these processes, Geobacter must transfer electrons outside the
cell onto metals or electrodes. This new research provides an explanation
of how this can happen.

Previous studies in Lovley’s laboratory demonstrated that Geobacter produces
fine, hairlike structures, known as pili, on just one side of the cell.
Lovley’s team speculated that the pili might be miniature wires extending
from the cell that would permit Geobacter to carry out its unique ability
to transfer electrons outside the cell onto metals and electrodes. This
was confirmed in a study in which microbiologist Gemma Ruegera teamed with
physicists Mark T. Tuominen and Kevin D. McCarthy to probe the pili with
an atomic force microscope. They found the pili were highly conductive. Furthermore,
when Geobacter was genetically modified to prevent it from producing pili,
Geobacter could no longer transfer electrons.

“These results help us understand how Geobacter can live in environments
that lack oxygen and carry out such unique phenomena as removing organic
and metal pollution from groundwater,” Lovley said. Geobacter can live in
the absence of oxygen because of its ability to transfer electrons outside
the cell onto iron minerals, which are natural constituents of most soils.
However, prior to the discovery of its conductive pili it was unknown how
this electron transfer might take place.

The conductive pili that Geobacter produces may have a variety of applications
for the electronics industry.
Ultrafine wires, often referred to as nanowires,
are required for further miniaturization of electronic devices. Manufacturing
nanowires from more traditional materials such as metals, silica, or carbon
is difficult and expensive. However, it is easy to grow billions of Geobacter
cells in the laboratory and harvest the microbial nanowires that they produce.
Furthermore, by altering the DNA sequence of the genes that encode for microbial
nanowires, it may be possible to produce nanowires with different properties
and functions.

Another interesting implication of this research is that it suggests a mechanism
for microbes to share energy in a mini-power grid. The nanowire pili of individual
Geobacter often intertwine, suggesting a strategy by which Geobacter might
share electricity.

Geobacter was discovered by Lovley in 1987 at the muddy bottom of the Potomac
River in Washington D.C., and over the past 18 years his research has earned
widespread media attention and major funding from government and private sources.
The tiny organisms, widely found in soils and aquatic sediments, have demonstrated
promise as cleaners of toxic spills and generators of energy. They are anaerobic
bacteria (living without oxygen) that use metals to gain energy the way
humans and other organisms use oxygen. They are distributed throughout the
world in a wide variety of soils and sediments. Geobacter have been used
to help remove contaminants from underground petroleum spills and landfill
pollution of groundwater, as well as remove uranium from contaminated groundwater
at a number of U.S. Department of Energy sites.

Source : www.physorg.com