Darwin thought of much of the evolutionary process as “endless forms most beautiful” and pretty much left out fungus.   Fungus development seems to be slow, but now we know the big breakthrough was at the end of the Carboniferous period about 290 million years ago.

Lignin Structure in Wood. Click image for the largest view.

Wood producing plants fix a huge amount of carbon during their lifetimes, building towering trees to small shrubs of decay resistant lignocellulose.  It’s that lignin that’s holding up massive biofuel development.

A study team of 70 researchers led by David S. Hibbett of Clark University, in Worcester, Mass., and Igor V. Grigoriev of the Department of Energy’s Joint Genome Institute has released a paper in Science that does a comparison study of the genomes of 31 fungi by performing deep phylogenetic sampling of fungal genomes and describing how white rot Agaricomycetes fungi have evolved an arsenal of enzymes to degrade lignin and unlock its stored carbon.

Turkey Tail White Rot Fungus. Click image for more info.

The study sheds a new light on how white rot fungi evolved the ability to degrade the recalcitrant plant biopolymer lignin. The findings provide an opening for researchers to use or reengineer fungal enzymes to advance biofuel production.

Scientists have already developed an arsenal of enzymes to attack the cellulose and hemicellulose, the primary components of plant cell walls, to get access to the component sugars that can be fermented into biofuels.

But when it comes to lignin, the irregularly cross-linked phenolic polymer in the cellulose matrix that provides strength and rigidity to plants, success has been limited, stalling cellulosic biofuel development.

White rot fungi are the only organisms capable of substantially decaying lignin, using peroxidase and other enzymes.  The study analysis uncovered a treasure trove of new enzymes to test and experiment with.

Science seems to have finally gotten to “first base” on the lignin problem.  There’s a long was to go, but a real step has just been made public.

As a side matter, of great interest by the way, by reconstructing the history of gene mutations, the team found that the first fungal peroxidases appeared 290 million years ago, at the same time that massive formation of coal ended. The finding suggests that the fungi’s acquired ability to degrade lignin altered Earth’s evolution, Hibbett says, by turning biomass into compost and subverting its fossilization into coal.

This new information offers a new perspective on the carbon cycle and suggests a huge array of quite interesting questions.  The obvious questions would center on the difference of the environment then and today if these fungi were evolved sooner, or not at all.  It also points out the potential massive change to the climate as white rot fungi pumped carbon back into the cycle essentially instantly rather than locking it away for millennia in coal.

More depth into fungi is going to be useful.  Not all of the species are studied and catalogued yet.  One day, not so far out there, the choices of enzyme potpourri for recycling biomass will be a market of great value.  And that revelation that the carbon cycle had a revolution 290 million years back is going to bedevil the climate change folks for years.


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