Biofuel From Fungi: Barnyard Poop Has Potential To Be Broken Down and Turned Into Energy

New research shows the fungi that grows naturally in the gut of sheep, goats and horses can help turn biomass into biofuel more efficiently. Ilya Naymushin/Reuters

Next time you pass a roadside farm, don't hold your nose. The source of that smell could fuel your car someday. Scientists have found out how to harness the power of fungi from the guts of horses, goats and sheep to break down biomass that can be used as fuel.

Researchers from the University of California, Santa Barbara, have learned that these anaerobic gut fungi perform as well as the best fungi engineered by industry to convert plant material into sugars that are easily transformed into fuel. "Nature has engineered these fungi to have what seems to be the world's largest repertoire of enzymes that break down biomass," says UCSB professor of chemical engineering Michelle O'Malley, the lead author on a study published in the February 18 issue of Science.

Companies wanting to turn biomass like wood, algae and grasses into fuel found that the molecules in plant cell walls—lignin, cellulose and hemicellulose—are impenetrable when combined. When they can't break it down, industry treats the biomass with heat or chemicals—or throws it away. Both options rack up the price of the finished product. But farm animals have no trouble breaking down these same molecules, the researchers noted, so they took a closer look.

They gathered manure from horses, goats and sheep at the Santa Barbara Zoo and a stable in Massachusetts. The enzymes found in the fungi from the manure contain proteins that work together to break down stubborn plant mass. It's not news to scientists that anaerobic gut fungi—some of the world's first nucleus-containing single-celled organisms—play a huge role in helping herbivores digest plants. They've been around since before the dinosaurs.

When these fungi reproduce, they release dozens of spores with tail-like appendages called flagella. These baby fungi swim around like tadpoles and find new food in the gut. They then trade tails for rootlike structures called hyphae, which dig into plant material. Then foliage becomes food.

O'Malley's team knew this but needed to enlist the help of the U.S. Department of Energy's Office of Science's Environmental Molecular Science Laboratory, at Pacific Northwest National Laboratory, as well as the DOE Joint Genome Institute. The latter sequenced the messenger RNA of several gut fungi to come up with their transcriptome, which represents all the possible proteins they could make. Then the Environmental Molecular Science Laboratory identified enzymes the fungi actually produce.

Industrial-variety fungi can create up to 100 enzymes, but gut fungi can produce hundreds more—which the researchers found were better at breaking down a hemicellulose found in wood, called xylan. When the scientists changed the fungi's diet from canary grass to sugar, the fungi responded by altering the enzymes it produced. In other words, the fungi can update their enzyme-producing repertoire on the fly.

Researchers say the findings suggest that industry could modify the gut fungi so that they produce improved enzymes that will outperform the best engineered fungi currently available, potentially leading to cheaper biofuels and bio-based products. "Because gut fungi have more tools to convert biomass to fuel, they could work faster and on a larger variety of plant material. That would open up many opportunities for the biofuel industry," O'Malley says.