Biomass Degradation in Fungus Gardens Nurtured by Leaf-Cutter Ants Analyzed

A team of researchers at the University of Wisconsin-Madison Department of Bacteriology have analyzed the enzymes involved in plant biomass degradation by a fungus that forms symbiotic relationship with leaf cutter ants.

Leaf-cutter ants form massive colonies that harvest hundreds of kilograms of leaves each year to cultivate microbial gardens composed primarily of the fungus Leucoagaricus gongylophorus. The fungus, in return, serves as the colony's primary food source via a plant biomass conversion. The understanding of this biomass degradation process and the microbial community mediating this process is limited.

The researchers analyzed the first draft genome of L. gongylophorus to investigate how plant biomass is degraded in the fungal gardens of both Atta cephalotes and Acromyrmex echinatior leaf-cutter ants. Metagenomic analysis showed that the fungus contains genes predicted to encode a diversity of enzymes that break down cellulose and hemicellulose, the complex sugars in plant cell wall. The study showed that the fungus produces distinct sets of enzymes throughout the different stages of biomass degradation, including numerous cellulases and laccases that may be involved in lignocellulose breakdown. According to the research team, these enzymes likely form the foundation of the symbiotic relationship.

The fungus-leaf cutter ant system is an important model for understanding how microbial communities degrade plant biomass in natural systems which is highly relevant for bioenergy research, given recent interest in cellulosic biofuels. The study was published in the June 15 issue of the journal Applied and Environmental Microbiology.