06/29/2012
Fungal End to Coal and the Carboniferous Period: A Possible Solution for Biofuels?
Phylogenetic sampling identifies key peroxidase.
The Science
Much of the world’s coal was generated 300 to 360 million years ago during the Carboniferous period. Wood (a major pool of organic carbon that is highly resistant to decay largely due to its lignin content) was deposited, transformed to peat, and eventually transformed to coal. But coal formation may also have declined from an unlikely source: fungi. These fungi had enzymes (ligninases) capable of degrading lignin, a category of enzyme important for the Department of Energy’s bioenergy mission, since lignin in plant biomass hinders biomass conversion to biofuels. An international team of scientists from Clark University and DOE’s Joint Genome Institute has proposed that a species of fungus, first appearing at about the end of the Carboniferous period, could more efficiently break down dead plant matter, possibly leading to the decline in coal formation. By comparing the genomic sequences of 31 fungi, including 12 sequenced for this study, the researchers showed that genes able to degrade lignin first appeared at the end of this period. Instead of becoming coal, the plant biomass decayed and the carbon was released into the atmosphere as carbon dioxide. This research provides insights into the origin of ligninases that can be used to develop processes for converting plant and tree biomass into bioenergy products.
Summary
Wood is a major pool of organic carbon that is highly resistant to decay, owing largely to the presence of lignin. The only organisms capable of substantial lignin decay are white rot fungi in the Agaricomycetes, which also contains non–lignin-degrading brown rot and ectomycorrhizal species. Comparative analyses of 31 fungal genomes (12 generated for this study) suggest that lignin-degrading peroxidases expanded in the lineage leading to the ancestor of the Agaricomycetes, which is reconstructed as a white rot species, and then contracted in parallel lineages leading to brown rot and mycorrhizal species. Molecular clock analyses suggest that the origin of lignin degradation might have coincided with the sharp decrease in the rate of organic carbon burial around the end of the Carboniferous period.
BER Program Manager
Ramana Madupu
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]
References
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