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Last Updated: Friday, 12 December, 2003, 11:37 GMT
Uranium bug has power potential
Geobacter sulfurreducens, University of Massachusetts
The biochemical tricks of Geobacter sulfurreducens are revealed
US scientists have decoded and analysed the genome of a bacterium which could help clear up radioactive waste and possibly even generate electricity.

The Geobacter species has genes that allow it to convert uranium and other radionuclides dissolved in water to solid compounds that can be extracted.

Its ability to manipulate electrons in metals could form the basis of a bio-battery, the US Energy Department says.

The genetic research on the bug is reported in the journal Science.

The organism, called Geobacter sulfurreducens, was found in a soil sample in Oklahoma that was contaminated by hydrocarbons - the breakdown products of fossil fuel combustion.

Researchers at The Institute for Genomic Research (Tigr) and the University of Massachusetts, Amherst, tell Science the bacterium has extraordinary capabilities.

Sense and move

The Massachusetts workers have previously shown that Geobacter species can precipitate a wide range of radionuclides and metals (including uranium, technetium and chromium) from groundwater, preventing them from migrating to wells or rivers where they may pose a risk to humans and the environment.

Now, the genomic research has given some insights into how this is possible.

Groundwater test, University of Massachusetts
The team has already shown how the bug can remove uranium from groundwater
G. sulfurreducens has 100 or more genes that appear to encode for various forms of c-type cytochromes. These are proteins that help move electrons back and forth.

They enable G. sulfurreducens to "reduce" metal ions - in essence adding electrons to positively charged metal atoms so that they become insoluble in water and precipitate as part of solid compounds.

These compounds are then more easily removed.

Small charges of electricity are also created through the reduction process and this has raised the possibility that Geobacter could form part of a bio-battery.

"We've provided a comprehensive picture that has led to fundamental changes in how scientists evaluate this microbe," said Barbara Methe, the Tigr researcher who led the genome project and is the first author of the Science paper.

"Research based on genome data has shown that this microbe can sense and move towards metallic substances, and in some cases can survive in environments with oxygen."

G. sulfurreducens was previously thought to be an anaerobic organism.

Nature's 'toolbox'

Massachusetts co-worker, Derek Lovley, who discovered the Geobacter group of bacteria, said: "Sequencing the genome of G. sulfurreducens has radically changed our concepts of how this organism functions in subsurface environments."

The genome analysis, he said, "revealed previously unsuspected physiological properties" of the bacterium and also gave scientists insight into the metabolic mechanisms that the organism uses to harvest energy from the environment.

"The genome of this tiny micro-organism may help us to address some of our most difficult cleanup problems and to generate power through biologically-based energy sources," Secretary of Energy Spencer Abraham said.

"Geobacter is an important part of Nature's toolbox for meeting environmental and energy challenges.

"This genome sequence and the additional research that it makes possible may lead to new strategies and biotechnologies for cleaning up groundwater at Department of Energy and at industry sites."

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