AMHERST, Mass. - Sugars can be converted to electricity with an efficiency much higher than previously known, according to researchers at the University of Massachusetts Amherst. Professor Derek Lovley and postdoctoral researcher Swades Chaudhuri have discovered a microorganism that is capable of stable, long-term electricity production by oxidizing carbohydrates. The organism, Rhodoferax ferrireducens, transfers electrons directly onto an electrode as it metabolizes sugar into electricity, producing carbon dioxide as a byproduct. Chaudhuri’s and Lovley’s findings will appear in the October issue of Nature Biotechnology.
Because sugars are a substantial component of many types of waste and carbohydrate-rich crops, such as corn, which are a renewable energy source, carbohydrates could become economical alternatives to fossil fuels in the production of electricity, according to Lovley.
“There’s been a lot of interest in microbial fuel cells trying to covert sugar into electricity,” Lovley said. “But in the past, they’ve converted 10 percent or less of the available electrons, and we’re up over 80 percent. And previous attempts to convert carbohydrates to electricity have required an electron shuttle, or mediator, which is typically toxic to humans.”
This organism doesn’t require a mediator because it attaches directly to the surface of the electrode, Lovley said.
“That’s one of the big advances,” he said. “People have done it without a mediator before, but their recovery of energy was less than 1 percent. And not having to use toxic elements is an obvious advantage in creating electricity. In the end, the electrons in the fuel cell are transferred to oxygen, so what we are really doing is putting a wire in between the microbe and the oxygen and harvesting this electron flow that otherwise would just go directly to oxygen.”
The organism was isolated in Lovley’s microbiology lab at the University of Massachusetts Amherst from aquifer sediments in Virginia during a U.S. Department of Energy study.
“We found that it had the unique ability to oxidize sugars with the reduction of iron oxides,” Lovley said. “This was of interest to us because last year we reported in Science that another group of iron reducers, known as Geobacter, could transfer electrons to electrodes. We reasoned that Rhodoferax might be able to do the same thing, which proved to be the case.”
The research was supported by the Office of Naval Research and the Defense Advanced Research Projects Agency, as well as the Department of Energy.
In theory, this method would allow a cup of sugar to power a 60-watt light bulb for 17 hours, but Lovley said the device needs improvement before it can be used commercially.
“There are still issues with getting a high enough voltage and converting the sugar to electricity fast enough,” he said. “Although the process is highly efficient, it is slow. And as the process is right now, we’re not talking about a lot of power. It’s barely enough to run a calculator, but we did it using unpolished graphite as a receptor. There are almost certainly better electroactive materials.
“The other thing that limits this is that the microorganisms have to attach to the surface of the receptor, so we’re working with polymer scientists, such as Tom Russell at UMass Amherst, to find a receptor with a maximally uneven surface, so more microbes can attach to it.
“I don’t want to give the impression that it’s ‘Back to the Future,’ where we stuff a banana in the engine and go, but it’s a pretty good leap from where microbial fuel cells were before.”
Derek Lovley can be reached at 413/545-9651 or firstname.lastname@example.org.