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Animal Poop Could Hold the Key to Better Biofuels

Biofuels come from breaking down plant matter, and digestive systems are quite good at doing that. But some creatures are better at it than others.

Scientists in search of better biofuels are increasingly poking around in the droppings of zoo animals. Ashli Brown, a biochemist at Mississippi State University, announced at a conference this week that she and her colleagues had found a biofuel-boosting bacteria in panda poop collected at the Memphis Zoo. And a team of Tulane University scientists found their butanol-producing bacteria after collecting samples from all manner of animal droppings at New Orleans’ Audubon Zoo. Why are scientists looking to zoo poop to improve biofuel production?

Because biofuels come from breaking down plant matter, and digestive systems are already very good at doing that. Ethanol, the most commonly produced biofuel, is a natural product of yeast’s digestive process. Yeast is very good at breaking down sugar, but plant material must be broken down to a simple sugar in order for the yeast to do its work.

Breaking down complicated carbons into sugars is exactly what digestive systems do. In middle school science class, teachers often have students hold a piece of white bread in their mouths. After a minute or so, it tastes sweet, like sugar. That’s because enzymes that live in the human mouth have broken the bread’s more complex carbohydrates down into glucose. The human body produces the enzymes that drive that particular process, but further down in the digestive track, bacteria produce enzymes that help break down other types of food.

Some creatures’ digestive systems are better at breaking down plant materials than others. Cows eat grass, and scientists have been reaching into their rumens to find the bacteria that digests it. Termites also digest wood effectively, so a team of government scientists travelled to Costa Rica, where legions of biodiverse species of termites swarm, in order to harvest bacteria from their guts. This guy, a marine crustacean called a gribble, doesn’t even need bacteria to break down wood: his body produces its own wood-digesting enzymes.

The Mississippi State University team headed to the zoo because pandas are on the A-list of animals that can process woody plants. It seemed likely that something living in a panda gut could do a better job at breaking down cellulose, one of the tougher-to-process types of plant material, than anything scientists had identified so far. The bacteria they found, Brown said in a press release, “may be more efficient at breaking down plant materials than termite bacteria.”

But, like yeast, bacteria can produce more than just sugar. Cow digestion, while good at breaking down plants, also produces methane. David Mullin, who led the research at Tulane, looked to zoos because he was searching for bacteria that could replace yeast as biofuel producers. He wasn’t looking for a bacteria that was more efficient at breaking down sugars, but one that could produce butanol, a biofuel that carries more energy than ethanol and is less corrosive.

“Bacteria that produce the biofuel butanol have been known for a long time. Our theory is that if there is one bacterial strain that produces butanol then there should be more,” Mullin says. “I decided to look in fecal matter of animals in the zoo under the theory that different exotic animals might have different constellations of bacterial strains in their intestines.”

He was right. As GOOD reported last week, the team found a bacteria that can produce butanol from a range of plant materials, including wood processed into newspapers.

The idea behind all of this research is to find a way to produce a greater volume of biofuels at a lower cost. One animal can have thousands of bacteria living in its gut, so there are many options out there. Visiting the zoo isn't a bad way to start.

Photo (cc) via flickr user kevindooley

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