Fungus Degrades Lignin In Bug Guts

In the gut of a beetle lies a fungus that helps the insect digest lignin, researchers have found (Proc. Natl. Acad. Sci. USA 2008, 105, 12932). The discovery could lead to more efficient and milder ways to convert plants into biofuels. Lignin is a natural aromatic polymer that protects a plant's sugar-containing cellulose and hemicellulose from most microbial attacks. It also vexes biofuel researchers who want easy access to the sugars. Ming Tien of Pennsylvania State University, University Park, and colleagues at various locations fed wood to the Asian longhorned beetle (shown), which bores into live trees, and the Pacific dampwood termite, which usually eats only dead wood. Analysis of the insects' feces showed that lignin had undergone propyl side-chain oxidation and demethylation in both species. For the termite, the researchers also observed aromatic ring hydroxylation. Tien and colleagues have identified the fungus in the beetle's gut, but they haven't yet found one in the termite's gut. They also found that chemical changes following lignin degradation in the beetle are similar to the changes observed in previously reported studies on lignin degradation by white-rot fungus. The researchers suggest that enzymes produced by a consortium of fungi and bacteria are likely responsible for overall lignin degradation by the insects.