Researchers discover key to bacterial bio-electricity production

Researchers at the University of Minnesota studying bacteria capable of generating electricity have discovered that riboflavin, commonly known as vitamin B-2, is responsible for much of the energy produced by these organisms. The bacteria, Shewanella, are commonly found in water and soil and are of interest because they can convert simple organic compounds such as lactic acid into electricity. The discovery means the development of efficient bio-fuel cells, or microbial fuel cells (MFCs), comes a step closer. Findings are published in the March 3 issue of Proceedings of the National Academy of Sciences.

The discovery means Shewanella can produce more power simply by increased riboflavin levels. Also, the finding opens up multiple possibilities for innovations in renewable energy - the production of clean power from biomass - and for environmental clean-up.

This is very exciting because it solves a fundamental biological puzzle. Scientists have known for years that Shewanella produce electricity. Now we know how they do it. - Daniel Bond, University of Minnesota's BioTechnology Institute

The interdisciplinary research team, which included several students, showed that bacteria growing on electrodes naturally produced riboflavin. Because riboflavin was able to carry electrons from the living cells to the electrodes, rates of electricity production increased by 370 percent as riboflavin accumulated.

Scaled-up MFCs using similar bacteria could generate enough electricity to clean up wastewater or power remote sensors on the ocean floor. Bacteria could help pay the bills for a wastewater treatment plant. But more ambitious applications, such as electricity for transportation, homes or businesses, will require significant advances in biology and in the cost-effectiveness of fuel cell materials. (An overview of recent developments in MFCs and their potential applications can be found here).

Why do these bacteria produce electricity? In nature, bacteria such as Shewanella need to access and dissolve metals such as iron. Having the ability to direct electrons to metals (schematic, click to enlarge) allows them to change their chemistry and availability:
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Bacteria have been changing the chemistry of the environment for billions of years. Their ability to make iron soluble is key to metal cycling in the environment and essential to most life on earth. - Jeffrey Gralnick, University of Minnesota's department of microbiology

The process could be reversed to prevent corrosion of iron and other metals on ships. Bond and Gralnick were each recently awarded funding from the U.S. Navy to explore this and other potential applications.

These electrochemical and analytical observations demonstrate that biofilms of Shewanella use secreted flavins in electron transfer to external acceptors, and that many environmentally relevant surfaces exposed to Shewanella are coated by electroactive flavins that may affect interactions with bacterial surface proteins. In metal-containing environments, flavin electron shuttling, metal chelation, and surface binding could act in concert to promote respiration and metal oxide dissolution phenotypes associated with this organism. Many activities catalyzed by Shewanella, and other organisms that secrete electroactive compounds, should be reexamined in light of this complex and ecologically important behavior. - Bond et. al.

This research was funded by the Initiative for Renewable Energy and the Environment, the National Science Foundation, the National Institutes of Health and Cargill.

The university's BioTechnology Institute is co-sponsored by the College of Biological Sciences and the Institute of Technology.

References:
Enrico Marsili, Daniel B. Baron, Indraneel D. Shikhare, Dan Coursolle, Jeffrey A. Gralnick, and Daniel R. Bond, "Shewanella secretes flavins that mediate extracellular electron transfer" [*.pdf], PNAS published March 3, 2008, 10.1073/pnas.0710525105

University of Minnessota: U of M researchers discover key for converting waste to electricity - March 3, 2008.

Biopact: Microbial fuel cell development speeds up: from biopower in space to the developing world - September 30, 2007