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DOE Pulse
  • Number 424  |
  • October 13, 2014

Who says an ant can’t make biofuels from that plant?

Leaf-cutter ants and fungus gardens. This image is protected by the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/) Photo by Austin Lynch.

Leaf-cutter ants and fungus gardens.

This image is protected by the
Creative Commons Attribution License

Photo by Austin Lynch.

Do leaf-cutter ants know the secret of producing biofuels without needing precious metals, high temperatures, or extreme pressures? On the floor of tropical forests, these ants cultivate tiny patches of land where bacteria and fungi turn leaves into sugars and other molecules. These molecules could serve as fuels or the precursors for them. Recently, a team from DOE’s Pacific Northwest National Laboratory and the DOE's Great Lakes Bioenergy Research Center made significant progress in disentangling the molecular details that underlie the conversion as well as the multispecies associations. They discovered that the bacteria and fungi, or microbes, gobble up the sugars and free amino acids first, leaving behind the harder-to-convert molecules.

"Understanding how bacteria turn plant matter into a source of energy could help improve biofuel production," said Dr. Kristin Burnum-Johnson, a PNNL bioanalytical chemist and co-author on the study. These investigations also show how the ants and their gardens influence larger environmental cycles.

The team studied gardens created by laboratory-reared ant colonies. The ants used fresh oak and maple leaves as manure to cultivate a fungus that produces specialized “swellings” that can feed the colony. They found that cellobiose and lignin derivatives, breakdown products resulting from the harder-to-digest materials, build up near the end of the degradation process. Their findings support their previous study, which detailed how the enzymes produced by the fungus break down lignocellulose in the leaves.

Their results also suggest urea and the amino acid arginine may play pivotal roles in the garden. Derivatives of urea may be an important source of nitrogen, especially when nitrogen is not readily available. For arginine, the key is its absence. No arginine was detected that was not associated with proteins. The lack of protein-free arginine suggests that this metabolite’s synthesis may be tightly regulated. The results provide insights into microbial community-level processes that underlie this important ant-fungus symbiosis.

"Although recent investigations have shed light on how plant biomass is degraded as it moves through the strata of fungus gardens, the goal of this study was to gain insight into the cycling of nutrients that takes place in these specialized microbial ecosystems," said Burnum-Johnson.

Future work elucidating the variations in metabolite profiles in wild colonies would provide important insights into the biomass degradation process in leaf-cutter ants.

Sponsors: The work was funded by DOE’s Office of Science, Office of Biological and Environmental Research, under PNNL's Pan-omics Program, and performed in EMSL, a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at PNNL. This work also was supported by the DOE Great Lakes Bioenergy Research Center.

Submitted by DOE’s Pacific Northwest National Laboratory