Spore Power


Where would we be without bacteria? Probably not here at all.  Certainly we’d have a harder time digesting food, the food chain would go unlinked, and our compost piles would never breakdown. However essential they may be, though, we have yet to exploit the tiny life forms as much as possible. Bacterial spores, it turns out, may very well be able to supply us with all the power the world might need.  

The skin of a bacillus spore is a wrinkly thing, giving the unborn bacterium a very raisiny appearance. When hit with a little moisture, those wrinkles unfold and the spores increase by as much as 40 percent. Ozgur Sahin, a professor of biological sciences and physics at Columbia University, had been studying the rigidity of this skin when it struck him that the change in size could by turned to profit.

“I said, ‘Wow this is an exceptional material—it must have a lot of mechanical energy to it,’” says Sahin. “I wrote some simple equations about how much energy they could theoretically produce. When I later looked up battery storage I saw that the numbers are not that far away.”

No need to add water to get the spores to do their thing: there’s enough natural evaporation to take care of that. “We have large areas of water—oceans, reservoirs—that constantly evaporate. You can simply rely on that process,” says Sahin. “It has quite a bit of power in itself. If I could find a way of coupling that with the motion of the spore skins, I could have access to that.”

Electricity is produced when a spore-covered rubber sheet bends and straightens in response to moisture. Image: Xi Chen/Columbia University




The mechanics are simple enough: Add some moisture to the air and the spores expand; take the moisture out of the air and they shrink back down. The bunching and unbunching of the spore’s skin provides a piston-like up and down as water and air go through the cycle that every grade school child ends up diagramming. “How much energy can you extract from that?” asked Sahin. “The spore is doing a good job.” But just how to go about harvesting the power from the spore was the tricky human problem.     

Sahin slapped some spores on the underside of a tiny cantilever and put them in an atomic force microscope. He engineered a device to change the humidity, “a small container with a wet towel.” Before he had a chance to use it, though, the spores began producing power. Sahin’s very breath, it turned out, provided enough moisture to change the size of the spores. They bent the cantilever and produced an output.

The spores Sahin used were engineered to produce twice as much energy as they would in their more natural form. Bacteriophobics can rest assured that their spore-coated, power-producing walls won’t become alive with cooties: Without access to the chemicals necessary for germination, there’s no chance of them turning to unexploitable mature bacteria. (The bacillus currently put to use is harmless.) Should spore power take off, it would be easy enough to breed variations that couldn’t germinate at all.

To maximize power, Sahin and his colleagues are thinking of ways to create a material entirely out of spores. Such a material could fold up like origami and unfold as the spores unwrinkle. Even without such heightened efficiency, the spores offer the only real method for harnessing the power of evaporation.

“From an energy point of view this is not small,” says Sahin. “On a per-unit-of-land basis, there’s more energy in evaporation than in wind.” And it could be done at much lower initial cost. The polymers you might coat with spores, and the spores themselves, are dirt cheap.

“So it is certainly possible that everything that we do could be powered by this evaporation process,” says Sahin.

Michael Abrams is an independent writer.

I wrote some simple equations about how much energy they could theoretically produce. When I later looked up battery storage I saw that the numbers are not that far away.

Prof. Ozgur Sahin,
Columbia University


June 2014

by Michael Abrams, ASME.org