Bacterial Batteries

How could a tiny electronic device made out of microscopic particles of silver be powered? Some researchers are taking their cue from the science fiction Matrix movies, in which humans are used as living batteries, and learning how to harness a living electrical source. Fortunately they are not using humans, as the movies portray; instead, they are creating microbial fuel cells and bacterial batteries.

Like any living organism, bacteria take in and expel energy. A colony of E. coli bacteria takes in carbohydrates, such as sugar, and breaks them down with enzymes. The bacteria release energy in the form of hydrogen, the same substance that fuels "green" cars. The electrical current comes in the form of a steady flow of electrons released as the microbe eats.

One company in England has made a fuel cell that is the size of a personal CD player. The bacteria inside feed on sugar cubes. Chemical reactions strip electrons from the hydrogen atoms to produce a voltage that can power an electrical circuit. To make it more cost-effective, re-

searchers are developing a second model that would be fueled by organic waste material, such as the leftovers from lunch. Currently, the microbial fuel cell is being used to power a small robot around the lab.

The U.S. Department of Defense is interested in another microbial fuel cell that uses a bacteria found on the bottom of the sea floor. Rhodoferax ferrireducens can convert more than 80 percent of the sugar it eats to electricity. The process is slow. One cup of sugar can light up a 60-watt bulb for seventeen hours, but the process to do so takes a week to charge up. The advantage to this slow process is that once it gets going, the battery continues to work without interruption—a good quality to have in a battery that is difficult to access. The Department of Defense is eyeballing microbial fuel cells to power electronic monitoring devices located at the

The electrical current released as a microbe eats can be harnessed to create efficient fuel cells like this one.

The electrical current released as a microbe eats can be harnessed to create efficient fuel cells like this one.

bottom of the ocean. These fuel cells would run off of the organic sediment found on the sea floor.

Other fuel cells are being adapted to power medical ventilators and generate electricity for pacemakers. The pacemaker battery would run off of glucose, the sugar found in the pacemaker-wearer's blood.

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