01/24/2011
Learning New Tricks from Fungi to Improve Biomass Processing
The Science
Knowing how biomass is degraded in nature will advance understanding in how to process biomass for conversion to biofuels. Most terrestrial biomass is sequestered in lignocellulose, the principal structural material of vascular plants. The biodegradation of plant material generally involves removal of the resistant lignin barrier that prevents enzymes from reaching cellulose and degrading it to sugar. However, brown rot fungi, natural biomass recycler in coniferous forests, degrade biomass without removing much of the lignin. DOE researchers at the University of Wisconsin, Madison, and the Great Lakes Bioenergy Research Center (GLBRC) in Madison, Wisconsin, report that these fungi can disrupt the lignin in wood even though it remains in place. Researchers used recently developed methods for solubilization and multidimensional 1H–13C solution-state NMR spectroscopy of ball-milled lignocellulose to analyse aspen wood degraded by Postia placenta. The results showed that decay decreased the content of the principal arylglycerol-β-aryl ether interunit linkage in the lignin by more than half, while increasing the frequency of several truncated lignin structures roughly fourfold over the level found in sound aspen. These results provide evidence that brown rot by P. placenta results in significant ligninolysis, which might enable infiltration of the wood by polysaccharide hydrolases even though the partially degraded lignin remains in situ. Recent work has revealed that the P. placenta genome encodes no ligninolytic peroxidases, but has also shown that this fungus produces an extracellular Fenton system. It is accordingly likely that P. placenta employs electrophilic reactive oxygen species such as hydroxyl radicals to disrupt lignin in wood.
Summary
Researchers discovered that key chemical linkages (ethers) in lignin’s complex molecular structure are broken, likely using reactive oxygen species such as hydroxyl radicals. They applied newly developed nuclear magnetic resonance (NMR) technology to look at the chemistry of wood attacked by a brown rot fungus. These results will enable development of new routes to access cellulose in biomass as part of the large-scale production of biofuels and will also improve understanding of natural carbon cycling from wood.
Principal Investigator
Kenneth E. Hammel
University of Wisconsin–Madison
References
Yelle, D., D. Wei, J. Ralph, and K. E. Hammel. 2011. “Multidimensional NMR Analysis Reveals Truncated Lignin Structures in Wood Decayed by the Brown Rot Basidiomycete Postia placenta,” Environmental Microbiology DOI:10.1111/j.1462-2920.2010.02417.x.