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Microbial Power Plants

© Neal Rolfe Chamberlain

Without electricity the industrialized world would come to a screeching halt. Have you ever been in a store that requires electric lighting because windows are lacking? The cash registers are electric and connected to a main computer that constantly updates the store's inventory. Store clerks go from aisle to aisle with little boxes that read the bar codes and automatically change the prices for certain products with the touch of a few buttons.

All this works very well until the electricity goes out. No electricity, and the store is dark and the cash registers do not function. In some stores the doors won't even open to let out the anxious customers from a lifeless dark cavern of what was once a thriving place of commerce.

Electricity is very important and people are always looking for new ways to generate it. In its simplest form electricity can be generated by any process that produces extra electrons. Basically, electricity is the movement of extra electrons from one end of a wire to another.

Microbes are in the electron-generation business as well. Rather than generate extra electrons to move down a wire, microbes obtain electrons from organic material (sugars, proteins, fats) and send them down a series of compounds (the electron transport chain or ETC), and as the electrons travel energy -- ATP -- is made.

Every electron that goes into the ETC must go out the ETC. At the end of the ETC is a final electron acceptor. In the case of microbes that can live in oxygen they use oxygen as the terminal electron acceptor. However, there are an enormous number of microbes that cannot live in an environment containing oxygen. In fact, for them oxygen is a deadly element. They must also get rid of the extra electrons they make in generating ATP.

A large number of a Geobacter species known as Desulfuromonas acetoxidans use iron as their terminal electron acceptor. Researchers at the University of Massachusetts reported in this week's issue of the journal Science that these microorganisms can transform organic matter commonly found at the bottom of the ocean into electrical energy.

What the researchers did was give the Desulfuromonas acetoxidans a graphite electrode instead of iron to serve as their terminal electron acceptor. Even though graphite does not occur naturally in the sediment at the bottom of Boston Harbor, Desulfuromonas acetoxidans was happy to use it as a terminal electron acceptor. These bacteria made so many electrons the researchers were able to produce enough electrical current to power a lightbulb or a simple computer.

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