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Sludge power

New Scientist

Keep your spaceship in running order with a sewage cocktail

Astronauts may one day be able to use their spacecraft's septic tank to keep in touch with ground control -- as long as they have plenty of sugar. Scientists in Michigan have developed a biofuel cell that creates a constant, low-power electricity supply by feeding glucose to common bacteria such as E. coli.

Biochemists Gregory Zeikus and Doo Hyun Park at Michigan State University in East Lansing have manipulated the bugs' metabolism to convert them into tiny powerhouses. They have built a 0.6 volt biofuel cell that can deliver currents of up to 17 milliamperes.

Bacteria normally break down glucose to generate adenosine triphosphate -- the main energy source for cells. This involves a flow of electrons, which the researchers have tapped into by adding a chemical called neutral red. Molecules of neutral red insert themselves into the bacterial membrane, where they hijack the reaction's electron-transport process, and shuttle electrons onto an electrode.

"It's like an electric plug," says Zeikus. "You put it in the cell membrane and put the cells in a cathode to make electricity." The method isn't likely to be powering your CD player any time soon, but Zeikus says it could be used as a backup method of maintaining communications in remote areas such as space. There is a bonus, too. Because some of the bacteria's energy is diverted to producing electricity, they don't multiply as fast as usual, leaving less sludge to dispose of.

Ziekus and Park are not the only researchers exploring the electrical potential of sugar-fed biofuel cells. Itamar Willner and his colleagues in the chemistry department of the Hebrew University of Jerusalem in Israel, for example, are using enzymes rather than bacteria to make batteries that could be implanted in people's bodies. Powered by blood sugar, the batteries could one day power pacemakers, insulin pumps and prostheses.

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Author: Nicole Johnston

Source: Applied and Environmental Microbiology (vol 66, p 1292)

New Scientist issue: 22nd April 2000

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