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Sugar high. Rhodoferax bacteria could harvest enough energy from a sugar cube to power a cell phone for 4 days.

Microbes Sweet on Making Power

If two microbiologists have their way, bacteria could be harnessed to generate electricity through the cutting-edge technology of fuel cells.

Like all fuel cells, microbe-based cells work by plucking electrons from fuel molecules and passing them to a battery or wire without burning the fuel. That makes the cells clean and efficient. But past microbe-based systems have been either too inefficient or too finicky to produce power on a large scale anytime soon. In 2001, for example, researchers reported that a species of Clostridium bacteria could siphon electricity directly from sugars, but the microbes converted a meager 0.04% of the available electrons in glucose to electricity.

In the September issue of Nature Biotechnology, Derek Lovley of the University of Massachusetts, Amherst, and his postdoc Swades Chaudhuri report that they've created a much more efficient microbial fuel cell. Lovley and Chaudhuri discovered their electron-shuttling bacteria while looking for bugs that might help remove uranium from groundwater below old nuclear weapons labs, researchers in Lovley's lab stumbled on a bacterium called Rhodoferax ferrireducens that passed electrons to iron, a uranium stand-in. To their surprise, the team members discovered that it happily downed a variety of sugars.

Lovley and Chaudhuri then placed a culture of Rhodoferax in one side of a two-chambered water tank. In each chamber they placed an electrode connected by a wire. When fed glucose and other sugars, the Rhodoferax grew and multiplied, completely coating the positively charged anode to which they passed the electrons they liberated from the sugars. In fact, they transferred up to 83% of the available electrons in sugar molecules.

That efficiency, record-breaking for microbes, is "very noteworthy," says Leonard Tender, an electrochemist and microbial fuel cell specialist at the Naval Research Laboratory in Washington, D.C. Still, Lovley and others caution that the technique is still far from becoming an industrial technology. One key hurdle: The bugs strip sugars of their electrons too slowly to supply practical amounts of current.

Related site
The Lovely lab site