Bacteria Muscle Into Renewable Energy Conversation

Ozgur Sahin dreams of a future when panels floating on lakes and oceans generate renewable energy. But the panels the biophysicist from Columbia University has in mind don’t harvest wind or sunlight. They use bacterial spores to tap the power of evaporating water.

In a step toward that goal, Sahin and his team have created machines that produce electricity when spore-laden materials—a sort of artificial muscle—expand and contract with changes in humidity (Nat. Commun. 2015, DOI: 10.1038/ncomms8346). Although these devices generate only about 1% of the energy produced by similarly sized commercial solar panels, the spore-powered generators cost about 100 times less, Sahin says.

The new devices rely on spores of Bacillus subtilis—soil bacteria that also populate human digestive tracts—glued to strips of commercially available polyimide films. In dry air, the spores contract and the polymer ribbons bend or coil. As humidity increases, the spores expand and the polyimide straightens. By controlling the material’s access to evaporating water, the team created artificial muscles that flex and relax.

Because the spores are rigid, the force they exert in swelling can be harnessed to run a generator.

“This work is remarkable,” says chemist Mingming Ma of the University of Science & Technology of China, who was not involved with the study. Ma, a pioneer in developing soft, hygroscopic materials for energy generation, adds that the power output from the artificial muscle machines is exquisite compared with what has been achieved with similar polymeric devices.

Sahin believes optimizing the chemistry of the adhesive holding the spores in place could further boost that output. The Columbia researchers use Elmer’s Glue, which is easier to work with than their first choice, poly-l-lysine. But both adhesives buckle under the force of the spores, sapping the efficiency of the generators.

“The glue problem, that’s a gap that can be closed,” Sahin says of the platform. “We really believe that this is a potential renewable energy source.”