03/20/2012
White Rot Fungus Sequence Provides New Understanding of Lignin Degradation
Efficient lignin depolymerization is unique to the wood decay basidiomycetes.
The Science
Lignin is a key building block in plant cell walls and one of the two most abundant biopolymers on Earth. It is also highly resistant to breakdown, complicating efforts to use plant biomass for producing biofuels. No animals and few fungi or bacteria are able to degrade lignin. However, the white rot fungus Ceriporiopisis subvermispora not only degrades lignin but leaves the cellulose in biomass intact. An international team of scientists has sequenced and annotated (assigned possible functions to genes) the genome of this fungus to learn more about its mechanisms of lignin degradation. Using experiments and a comparison with the sequence of its more studied relative Phanaerochaete chrysosporium, the scientists identified differences in the degradation genes between the two fungi and developed new hypotheses about the mechanisms that enable these fungi to target lignin but not cellulose. These results may assist in the development of improved pathways for the conversion of biomass to biofuels as well as provide improvements in deconstruction of wood for the pulp and paper industry. The study included researchers at the DOE’s Joint Genome Institute (DOE-JGI).
Summary
Many microorganisms are capable of using cellulose and hemicellulose as carbon and energy sources, but a much smaller group of filamentous fungi in the phylum Basidiomycota has also evolved with the unique ability to efficiently depolymerize and mineralize lignin, the most recalcitrant component of plant cell walls. Collectively known as white rot fungi, they remove lignin to gain access to cell wall carbohydrates for carbon and energy sources. These wood-decay fungi are common inhabitants of fallen trees and forest litter. As such, white rot fungi play a pivotal role in the carbon cycle.
References
Fernandez-Fueyo, E., et al. 2012. “Comparative Genomics of Ceriporiopsis subvermispora and Phanerochaete chrysosporium Provide Insight into Selective Ligninolysis,” Proceedings of the National Academy of Sciences of the United States of America 109(14), 5458–63. DOI:10.1073/pnas.1119912109.