Turkey tail (bottom) is a peroxidase-producing white rot fungus capable of decaying the tough biopolymer lignin in wood, as seen in this scanning electron micrograph image of a fungus-ravaged aspen sample.
A comparative study of the genomes of 31 fungi has shed light on how white rot fungi evolved the ability to degrade the recalcitrant plant biopolymer lignin (Science, DOI: 10.1126/science.1221748). The findings provide an opening for researchers to use or reengineer fungal enzymes to advance biofuel production.
Scientists already have an arsenal of enzymes to attack cellulose and hemicellulose—the primary components of plant cell walls—to get the component sugars that can be fermented into biofuels. But when it comes to lignin, the irregularly cross-linked phenolic polymer in the cellulose matrix that provides strength and rigidity to plants, success has been limited.
White rot fungi are the only organisms capable of substantially decaying lignin, using peroxidase and other enzymes. The study, by a team of 70 researchers led by David S. Hibbett of Clark University, in Worcester, Mass., and Igor V. Grigoriev of the Department of Energy’s Joint Genome Institute, took a systematic look at fungal genes that code for lignin-busting enzymes. The analysis uncovered a treasure trove of new enzymes to test and tinker with.
In addition, by reconstructing the history of gene mutations, the team found that the first fungal peroxidases appeared 290 million years ago, at the same time that massive formation of coal ended. The finding suggests that the fungi’s acquired ability to degrade lignin altered Earth’s evolution, Hibbett says, by turning biomass into compost and subverting its fossilization into coal.