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Saturday, October 1, 2016

Geobacter bacteria clean up nuclear waste and generate biodiesel & electricity

Researchers from the University of Massachusetts, Amherst have recently engineered Geobacter metallireducens, a bacterium that can feed with hydrogen and carbon dioxide to produce electricity. 

 Geobacter metallireducens
“This represents the first result of current production solely on hydrogen,” says Amit Kumar, who worked with Derek Lovely, the scientist who first isolated Geobacter metallireducens 26 years ago, in the Potomac River.
Geobacter species are of interest because of their bioremediation, bioenergy potential, novel electron transfer capabilities, the ability to transfer electrons outside the cell and transport these electrons over long distances via conductive filaments known as microbial nanowires.
By studying a relative of Geobacter metallireducens called Geobacter sulfurreducens, Kumar and the team produced electricity by having the bacteria reduce organic carbon compounds with a graphite electrode like iron oxide or gold to serve as the only electron receptor. The bacteria they chose for engineering did not have the need for carbon to grow in a microbial fuel cell.

Allison Speers, MSU graduate student, works on a fuel cell that can eliminate biodiesel producers' hazardous wastes and dependence on fossil fuels. Image by Kurt Stepnitz.
MSU microbiological Gemma Reguera, a co-author on the study, developed patented adaptive-engineered bacteria called Geobacter sulfurreducens. Geobacter are naturally occurring microbes that have proved promising in cleaning up nuclear waste and in improving other biofuel processes.
Geobacter shield themselves from uranium by producing hair-like filaments that attract and bind the uranium very strongly,” Reguera said. “The bacterial hairs are fully charged with electricity, just like a live electrical wire, and zap the uranium. And what happens next is simple chemistry - the soluble, dangerous uranium is immobilised onto the wires as a mineral. This prevents its spread and protects us from exposure.”
Reguera, along with lead authors and MSU graduate students Allison Speers and Jenna Young, evolved Geobacter to withstand increasing amounts of toxic glycerol. They then searched for partner bacteria that could ferment it into ethanol while generating by-products that ‘fed’ the Geobacter.
“It took some tweaking, but we eventually developed a robust bacterium to pair with Geobacter,” Reguera said. “We matched them up like dance partners, modifying each of them to work seamlessly together and eliminate all of the waste.
“[The bacteria] feast like they’re at a Las Vegas buffet. One bacterium ferments the glycerol waste to produce bioethanol, which can be re-used to make biodiesel from oil feedstocks. Geobacter removes any waste produced during glycerol fermentation to generate electricity. It is a win-win situation.”

Image courtesy of Gemma Reguera.
The microbes are the featured component of Reguera’s microbial electrolysis cells, or MECs. These fuel cells do not harvest electricity as an output - rather, they use a small electrical input platform to generate hydrogen and increase the MEC’s efficiency even more.
Through a Michigan Translational Research and Commercialization grant, Reguera and her team are now developing prototypes that can handle larger volumes of waste. She is also in talks with MBI, an enterprise operated by the MSU Foundation, to develop industrial-sized units that could handle the capacities of a full-scale biodiesel plant.
“Traditional approaches see producers pay hefty fees to have toxic wastewater hauled off to treatment plants,” Reguera said. “By cleaning the water with microbes on-site, we’ve come up with a way to allow producers to generate bioethanol, which replaces petrochemical methanol. At the same time, they are taking care of their hazardous waste problem.”

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