Bug Droppings Provide Important Clues for Energy Research Team That Includes ODU's Hatcher
A multi-university collaboration of energy researchers, including Patrick G. Hatcher, a geochemist from Old Dominion University, has found in the digestive tracks of termites and beetles a possible solution to a problem that has thwarted efforts to create alternative fuels from trees and other woody plants.
Their paper, "Lignin Degradation in Wood-feeding Insects," debuted in Proceedings of the National Academy of Sciences (PNAS) Early Edition on Monday, Aug. 18. Other authors of the paper come from Penn State University, Purdue University and the University of Tsukuba in Japan.
"The evidence is in the poop of termites and beetles," said Hatcher, the Batten Endowed Chair in Physical Sciences whose research group at ODU helped to do the instrument analysis that turned up a surprising finding. Contrary to the results of previous studies, this research found that enzymes in the guts of certain bugs can quickly break down lignin-a polymer, like a natural plastic-in order to expose the cellulose that is food for the bugs.
Most of the alternative vehicle fuel produced from biomass in the United States is ethanol made from corn kernels, which are easy to mash up and ferment. But the corn-to-ethanol boom has been blamed for higher food costs worldwide, as well as for deleterious environmental impacts and inefficiencies. Furthermore, energy experts point out that there will never be enough corn to produce the amount of fuel needed to significantly cut consumption of fossil fuels.
Scientists and engineers have long known that non-food or waste plant matter, perhaps corn stalks or junk wood that is a byproduct of forest maintenance, contain cellulose that also can be broken down into glucose and fermented into ethanol. Use of this biomass would not drive up food costs and would not have many of the environmental drawbacks of current ethanol production from corn crops. Even better, there is a huge supply of surplus woody plant matter.
So why does the ethanol in our gasoline still come from corn kernels? The answer is lignin and starch. Corn kernels contain almost no lignin and the starches are readily converted to glucose and then to ethanol; corn stalks contain quite a bit of lignin and cellulose that is not easily converted to glucose.
Think of lignin as a shell protecting a tasty morsel. It is the stiff material that props up cellular walls and allows trees or corn stalks to stand upright. In doing its job, however, lignin throws up a stiff defense of the cellulose that it links up with. Once this defense is broken, energy researchers still must contend with the fact that cellulose itself is not easily fermented.
Existing processes for the production of cellulosic ethanol therefore require harsh and expensive chemical or microbial treatments to first degrade the lignin, and then to break down the long cellulose molecules into their glucose units so fermentation can begin.
"It was previously thought that lignin was not degraded by the guts of termites and beetles," explained Hatcher.
Earlier studies have suggested that wood-feeding insects overcome the lignin barrier by relying upon wood-degrading fungi. In other words, the insects wait for wood to rot-and the lignin to degrade-before they dine. But the authors of this latest paper also know that certain insects, such as the Asian longhorned beetle that they studied, can feed on the inner wood of living, healthy trees. This presented a mystery that they wanted to investigate.
"My colleagues at Penn State, Ming Tien and Kelli Hoover, proposed that we look at this. They sent their graduate student, Scott Geib, down here with samples and he worked with my research group on the analysis," Hatcher said.
Geib is first author of the paper in PNAS. Tien, professor of biochemistry, and Hoover, professor of entomology, also are authors. Rachel Sleighter, who is a doctoral student of Hatcher at ODU, and whom he described as "one of the bright lights in our chemistry department's new Ph.D. program," is among the other authors.
Hatcher directs ODU's College of Sciences Major Instrumentation Cluster (COSMIC) laboratory, and the Penn State researchers wanted to utilize the Hatcher group's analytical expertise in nuclear magnetic resonance (NMR). But Hatcher suggested a preliminary step, an analysis called tetramethylammonium hydroxide (TMAH) thermochemolysis. He is internationally known for his use of this process, which segments very large molecules so they can be analyzed more precisely by gas chromatography and mass spectrometry.
"When we did this with the samples of poop, we said, 'Gee, this looks like the lignin is oxidized,'" Hatcher said. "These insects have enzymes in their guts that allow them to digest not only cellulose, but also degrade the lignin. This is a mechanism for depolymerization. If we can understand the way the enzymes work to depolymerize the lignin and release cellulose, then we could make the enzymes and employ them in the processing of cellulose in fresh wood."
After all, he added, "The bugs are trying to get energy from the cellulose, and we are too."
As executive director of the Virginia Coastal Energy Research Consortium (VCERC), Hatcher also is leading an initiative based at ODU to use algae for the production of biodiesel fuel.