Back-of-the-envelope calculations suggest the microbes in a termite’s gut can transform a sheet of standard-size office paper into a half-gallon of hydrogen. The miracle is the enormous amount of potential flatulence doesn’t cause the bug the least bit of indigestion. Instead, the insect uses the energy-rich molecule for fuel.
For some time, scientists have tried to get a handle on how insects barely the size of a grain of rice can reduce entire houses and even forests to pulp. Of particular interest are the hundreds of bacteria species that colonize the bug’s tiny gut and that have long been suspected of playing some role. If scientists can sort out the details of the process, they may be able to reproduce it, scale it up and make giant termite-gut reactors that pump out clean fuels.
Last week a large team of scientists published the results of a fairly audacious undertaking: they isolated and sequenced genome fragments from the entire population of bacteria in the termite hindgut. Then they analyzed the DNA and proteins to provide the most comprehensive picture yet of exactly what goes on in the dark reaches of a termite’s plumbing.
"It turned out to be a gold mine in there," said Jared Leadbetter, an environmental microbiologist at Caltech who led the international effort.
In a droplet of swill small enough to fit on the head of a pin, the team identified nearly 100 different species of bacteria of the type known as spirochetes—twisty corkscrew-like microbes belonging to the group of germs that cause syphilis and Lyme disease. They also found a large share of fibrobacters—relatives of bacteria that live in cow stomachs and help to digest grass.
After sequencing and analyzing more than 80,000 genes from the bacteria, the team found nearly 1,000 genes that play roles in breaking down two of wood's main components—cellulose and xylan—into smaller sugars.
That’s no small feat. Wood is a stiff material that’s built to last. Taking it apart is a challenge, and termites are among the few known animals that can do it. The insect chomps the wood into bits, but the real work—the breakdown of cellulose and xylan—requires an arsenal of enzymes, because wood contains tightly intertwined compounds.
"This project has really given me a new appreciation for the lowly termite," said Phil Hugenholtz, a collaborator at the Department of Energy’s Joint Genome Institute. "It’s a mobile, miniature bioreactor."
Indeed, at the heart of the discovery are the proteins the bacterial genes encode. Many are enzymes that take part in complex cascades of biochemical reactions, which convert one compound to another through a series of steps. Enzymes make reactions progress faster and with less energy. Along the way, byproducts like hydrogen or other useful substances are often given off.
Even so, "adapting these findings to an industrial-scale system is far from easy," said JGI Director Eddy Rubin. Termites might be able to efficiently convert wood into fuel in their tiny bioreactor hindguts, he said, but "scaling up this process so that biomass factories can produce biofuels more efficiently and economically is another story."
Caltech’s Leadbetter believes the challenge lies in events at the start of the process, like those involved in breaking down cellulose and xylan. He and his colleagues believe that investigating the genes at the front end of those initial reactions will eventually lead to better ways to manufacture biofuels.
In the meantime, the group’s massive genome collection lies in a public database for use by a growing number of researchers who are looking for solutions to global warming in the most unlikely places.
—Leslie Fink, NSF
This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report.