Certain bacteria are capable of generating an electrical current as they convert
organic material into energy.
Photograph by Gary Bartholomew/CORBIS
Petroleum, a major source of energy, comes from organic matter. Other kinds
of organic material are also a large potential source of energy, but not all are
as easy to utilize as petroleum.
Now, the researchers have found that bacteria in a
family of microorganisms called Geobacteraceae can serve as a source of energy
as they break down organic material—anything from decaying plant and animal
matter to toxic organic pollutants such as benzene.
The bacteria break down organic matter to obtain
energy, and in the process they produce a stream of electrons that, if captured,
can produce electricity. Normally the bacteria just transfer the electrons to
minerals rich in iron. To tap into the electron supply, University of
Massachusetts–Amherst microbiologist Derek Lovley and his colleagues offered
the bacteria another place in which to dump their electrons: a graphite disk.
The scientists filled fish tanks with mud taken from Boston Harbor, which has
heavy concentrations of polluted sediment, and buried part of a makeshift
battery in the sludge.
The battery was made up of a graphite anode (the negative terminal), which
was buried in the mud, and a cathode (positive terminal) in the seawater, both
connected by a copper wire.
The bacteria in the mud stripped electrons from surrounding organic compounds
and transferred the electrons to the anode. The electrons flowed through the
copper wire to the cathode, just as they would in a battery, producing an
electrical current.
Lovley found that over time, the bacteria congregated
on the graphite disk, producing a steady—if weak—supply of electricity.
A report on the research was published in the January 18 issue of the journal
Science.
The bacteria were already known to be capable of
another important function. They can degrade toxic organic pollutants such as
benzene—a carcinogenic component of petroleum contamination—and convert them
into carbon dioxide.
Although this ability to degrade toxic aromatic hydrocarbons was previously
recognized, Lovley said the new study will advance knowledge of how to benefit
from the process.
Moreover, he added, the genome sequences of several bacteria in the
Geobacteraceae family are now known, which may help scientists engineer more
efficient bacteria that degrade pollutants more quickly.
Bioremediation, or the use of organisms to clean up pollutants, is gaining
popularity as a cheaper and environmentally more benign method of removing toxic
pollutants.
Much of the work in Lovley's laboratory centers on finding ways to clean up
uranium contamination from atomic weapons production. Uranium poses a particular
problem because it dissolves in water and contaminates groundwater.
Lovley has found that microbes from the Geobacteraceae family strip a couple
of electrons from a form of uranium and convert it into a less harmful form that
is not soluble and therefore does not contaminate underground water supplies.
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