Pulp NonFiction: Fungal Analysis Reveals Clues for Targeted Biomass Deconstruction

Without fungi and microbes to break down dead trees and leaf litter in nature, the forest floor might look like a scene from TV’s “Hoarders.” Dan Cullen, research microbiologist at the FPL, is part of an international team of scientists studying the genomic make-up of two fungi species that are especially talented when it comes to clean-up.

Phanaerochaete chrysosporium and its close relative Ceriporiopisis subvermispora can selectively break down the cell wall components cellulose and lignin—the number one and two most abundant biopolymers on Earth. Both fungi species are found all over the world and are of interest to bioenergy researchers because they possess enzymes that can break down plant biomass and could therefore be useful for accelerating biofuels production.

In a study published online in the Proceedings of the National Academy of Sciences, the team presented a comparative genomic analysis of the two white-rot fungi, whose genomes were generated and annotated at the Department of Energy’s (DOE) Joint Genome Institute (JGI). The study revealed substantial differences among the sets of genes involved in lignocellulose degradation, providing further insight into the mechanics of how white rots do their dirty work.

“The fact that we have such a large group of people involved in this project is a clear demonstration that there’s certainly interest in enzyme discovery,” said Cullen, study senior author and long-time DOE JGI collaborator.

Cullen and his colleagues compared the fungal genomes to learn more about the basis of C. subvermispora’s ability to selectively break down lignin. Understanding this process is of longstanding interest to the pulp and paper industry. According to the American Forest & Paper Association, approximately $175 billion worth of forest products such as pulp and paper are produced annually, and account for five percent of the Nation’s GDP.

Kent Kirk, a former FPL researcher who is considered a leading figure in the study of lignin degradation by fungi, provided perspective on how the current research could impact the pulp and paper industry. “This grew out of fundamental research by the University of Minnesota and FPL where they applied the concept of ‘biopulping,’ the partial decay of wood by lignin-degrading fungi to decrease the energy required for mechanical pulping. Cerioporiopsis subvermispora quickly became the ‘biopulper’ of choice.”

Kirk described how wood chips treated with the fungus for two weeks required 30% less energy for pulping than untreated chips and how outdoor trials were repeatedly successful at the 50-ton scale. “The technology has not yet been commercially adopted, but as energy costs continue to rise, it should be increasingly attractive for implementation,” Kirk said.

Analyzing the diversity of wood-decaying fungi and cataloging enzymes involved in lignocellulose degradation is one of the goals of the DOE JGI Fungal Genomics Program led by Igor Grigoriev. “We are in the process of conducting functional comparative genomics of more than 20 such fungi sequenced or currently being sequenced at the DOE JGI,” he said. “This should provide us a better understanding of the diverse and complex mechanisms of lignocellulose degradation in fungi, the influence of these mechanisms on carbon cycling in the forest ecosystem, and ultimately lead to improvements in biopulping.”

Cullen sums up the collaborative work of the DOE JGI team and their interest in these fungi, “In this particular case, one would come away thinking more about the role of white-rot fungi in the carbon cycle. Lignin is a recalcitrant compound in forest ecosystem biomass and very few fungi have the capability to degrade lignin. Even fewer fungi have the ability to selectively remove lignin at such an efficient rate. C. subvermispora is one exception in its ability to do just that.”

# # #

By Rebecca M. Wallace, FPL Public Affairs Specialist