Leafcutter ants may provide cellulosic solution

By Craig A. Johnson | December 09, 2009
Finding natural solutions to difficult chemical conundrums is the purpose of the Great Lakes Bioenergy Research Center in Madison, Wis. Researchers there are looking to leafcutter ants for new enzymatic processes that will further efforts to commercialize cellulosic ethanol. The ants, which are found in tropical climates and live in enormous colonies with populations that can number in the millions, have evolved several features over time that make their particular cocktail of enzymes attractive to researchers.

Leafcutters are considered a pest for most agricultural operations in Central and South America. "A mature colony can defoliate a tree overnight," said Garret Suen, a post doctoral research fellow at the GLBRC. "They're really a major agricultural pest in the tropics. Anyone who farms oranges or papaya loathes leafcutters. If they get into a grove, they can devastate it overnight."

It may seem counter-intuitive to look to such a destructive pest for an economic benefit to ethanol production, but this tiny nuisance could also provide a big benefit from the enzymes it creates. Converting plant cell walls into simple sugars is a major challenge for scientists and leafcutter ants, which tend massive fungal gardens of their decaying byproducts, may present a worthwhile solution. Researchers at the GLBRC are studying multiple enzymes used by the ants in the fungal gardens to craft the perfect cocktail for ethanol production. "That cocktail is probably a mixture of about six or seven enzymes," Suen said. "One is definitely a cellulase that does the majority of the breaking of the beta -1,4 glycocitic link between the glucose and cellulose chain. But then there are other things, such as cellulose-binding modules, a protein which binds the cellulose itself, and then allows the cellulase to do its job."

The researchers recently received a U.S. DOE grant to further study this cellulosic possibility, but prior to receiving the grant the GLBRC was already studying the unique symbiotic relationship between the ants and their fungal gardens. Over 50 million years, the ants and the fungus have evolved to the degree that if the ants were to die, or are removed from the system, the fungus dies as well, and vice versa. "The fungus-growing ant system is obligate, and one of the most complex symbioses that's described in nature," Suen said.

Research at the GLBRC is providing a new look at some very old progress made in the ants' natural communities. With the leafcutter ants, the mixture of enzymes works in balance, but that nuanced formula would be nearly impossible to synthesize in a lab. "There is a renaissance, and researchers are going back to natural communities—an area called natural products. These are novel compounds in that no one has ever seen them before," Suen said.