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Monday, October 29, 2007

Alternative fuel :Microbes Plus Sugars Equals Hydrogen Fuel?

To isolate bacteria present in swine waste samples, microbiologists Rhonda Zeltwanger and Michael Cotta work in an anaerobic glove box. Because most of these bacteria are strict anaerobes, many manipulations must be performed in the absence of oxygen. (Credit: USDA, Photo by Keith Weller)

Wanted: Bacterium that can eat sugar or sludge; must be team player or electrochemically active; ability to survive without oxygen, a plus. Thus might read the bacterial "job description" posted by Agricultural Research Service (ARS) and Washington University (WU) scientists, who are collaborating on ways to make microbial fuel cells more efficient and practical.

According to Mike Cotta, who leads the ARS Fermentation Biotechnology Research Unit, Peoria, Ill., the project with WU arose from a mutual interest in developing sustainable methods of producing energy that could diminish U.S. reliance on crude oil.

Cotta's team specializes in using bacteria, yeasts or other microorganisms inside bioreactors to do work, such as ferment grain sugars into fuel ethanol. At WU in St. Louis, Mo., assistant professor Lars Angenent is investigating fuel cell systems that use mixtures of bacteria to treat organic wastewater and catalyze the release of electrons and protons, which then can be used to produce electricity or hydrogen fuel.

In September 2006, the researchers pooled their labs' resources and expertise to undertake a three-year cooperative project. One resource they'll share is the ARS Peoria-based Microbial Culture Collection, which houses about 87,000 accessions of freeze-dried microbes from around the world.

Using the collection's database information, the team is searching for microbes that "eat" biomass sugars (e.g., glucose and xylose from corn stover) and are electrochemically active. That means they can transfer electrons from fuel cell sugars without help from costly chemicals called mediators. The electrons, after traveling a circuit, combine with protons in a cathode chamber, forming hydrogen, which can be burned or converted into electricity.

Bacteroides and Shewanella are among bacteria species used to start the process.

Hydrogen's appeal stems from its natural abundance and capacity to store and release energy in a nonpolluting manner. The challenge is commercially producing it from sources other than fossil fuels, which are in limited supply and nonrenewable. About 95 percent of U.S. hydrogen comes from petroleum or natural gas via a process called steam reforming.

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