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Amadouvier du pin. © INRA

Evolution: prehistoric fungus could explain the end of coal formation

A fungus that decomposes wood and which appeared nearly 300 million years ago might offer a partial explanation as to why vegetation-based coal formation stopped during this same period. This is one of the conclusions of a study by researchers from INRA, CNRS and the Universities of Lorraine and Aix-Marseille as part of an international consortium. The study provides insight into the wood degradation process by modern fungi, which could be of particular interest to the biofuels industry. The results were published in the 29 June 2012 issue of Science.

By INRA News Office, translated by Teri Jones-Villeneuve
Updated on 02/26/2013
Published on 06/29/2012
Keywords: wood - fungus - coal

Saprotrophic fungi (which feed on organic matter) play a major role in forest ecology. These organisms break down decaying matter (leaves, wood, other organisms, etc.) and help recycle carbon in the ecosystem, a necessary element in the development of living things. Among saprotrophic organisms, white rot fungi, such as polypores, break down lignin and cellulose in the cell walls of wood, while brown rot fungi, such as Serpula lacrymans, mainly break down polysaccharides in wood, or the cellulose and hemicellulose. By acting together, these wood-eating (or xylophagous) fungi can decompose both the lignin and cellulose in wood. They are essential to maintaining balance in the forest environment by transforming organic matter into humus that can be reused by plants.

Researchers from INRA teamed up with a group of scientists from CNRS and Aix-Marseille Université as part of a major project that involved sequencing the genomes of some thirty forest-dwelling saprotrophic fungi, led by the Clark University and the Joint Genome Institute in the United States. The research teams analysed the genome sequence of dozens of white and brown rot species. By comparing the repertoire of the fungi’s genes, the scientists were able to characterise the various mechanisms the fungi use to break down lignin and cellulose.

They were then able to reconstruct the arsenal of enzymes used by the first fungus able to digest wood lignin, which would have lived some 300 million years ago. This new biological capability changed the world: by efficiently decomposing dead wood, this fungus and its descendants ended the accumulation of carbon that until then would have resulted in coal formation. When organic wood matter is not broken down, it becomes fossilised and produces coal. Most coal deposits were formed during the Carboniferous period, which lasted about 60 million years and ended 300 million years ago – a time that coincides with the appearance of the first xylophagous fungi.

These results offer a better understanding of forest fungi ecology, confirming the link between its role in forest ecology, biological characteristics and gene repertoire. They will also further applied research on second generation biofuels (obtained from trees), because the breakdown of cellulose and lignin is an important step in transforming wood into biofuel.

INRA News Office, translated by Teri Jones-Villeneuve
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Dimitrios Floudas et al. The Paleozoic origin of enzymatic lignin decomposition reconstructed from 31 fungal genomes., 29 June 2012.