As spring warms up Wisconsin, humans aren't the only ones tending their gardens. At the University of Wisconsin-Madison Department of Bacteriology, colonies of leaf-cutter ants cultivate thriving communities of fungi¹ and bacteria using freshly cut plant material.

 

While these fungus² gardens are a source of food and shelter for the ants, for researchers, they are potential models for better biofuel production.

 

"We are interested in the whole fungus garden community, because a lot of plant biomass goes in and is converted to energy for the ants," says Frank Aylward, a bacteriology graduate student and researcher with the Great Lakes Bioenergy Research Center.

 

Aylward is the lead author of a study identifying new fungal enzymes³ that could help break down cellulosic（有纤维质的） -- or non-food -- biomass for processing to fuel. His work appears on the cover of the June 15 issue of the journal Applied⁴ and Environmental Microbiology.

 

"All the enzymes that we found are similar to known enzymes, but they are completely new; no one had identified or characterized them until now, " Aylward says.

 

Building on Aylward's previous study of these gardens, the researchers relied on genome sequencing provided by the U.S. Department of Energy Joint⁵ Genome Institute (JGI) and support from Roche Applied Science's 10 Gigabase Grant Program to understand the unique roles of fungi and bacteria. In addition to sequencing the genome of Leucoagaricus gongylophorous, the fungus cultivated by leaf-cutting ants, the researchers looked at the genomes of entire, living garden communities.

 

"We really tried as thoroughly⁶ as possible to characterize the biomass degrading enzymes produced," Aylward says. "Identifying all these new enzymes really opens the door to technological⁷ applications, because we could potentially mix and match them with others that we already know about to achieve even better biomass degradation⁸."

 

In a symbiotic⁹ relationship, L. gongylophorous provides food for the leaf-cutter ant Atta cephalotes by developing fruiting bodies rich in fats, amino acids and other nutrients¹⁰. To fuel production of these fruiting bodies, the fungus needs sugar, which comes in the form of long cellulose molecules¹¹ packed inside the leaf clippings the ants deliver. To get at the sugars, the fungus produces enzymes that break the cellulose apart into glucose¹²（葡萄糖） subunits.

 

After sequencing the L. gongylophorous genome, the researchers noticed that the fungus seemed to be doing the lion's share of cellulose degradation with its specialized¹³ enzymes. However, they also realized that it was by no means working alone: in fact, the gardens are also home to a diversity of bacteria that may help boost the fungus's productivity.

 

"We think there could potentially be a division of labor¹⁴ between the fungus and bacteria," says Garret Suen, co-author of the study and a UW-Madison assistant professor of bacteriology and Wisconsin Energy Institute researcher.

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