Rot Is Hot to Trot: Brown Rot Fungi Cries “Tora! Tora! Tora!” to Biomass

by Jim Lane (Biofuels Digest) ... When it comes to fungi, their ability to break even the most recalcitrant of hardwoods down is well-documented and anyone who has spent a day in a rainforest knows it. But there’s rot and there’s rot when it comes to fungi. That is, there’s white rot and brown rot.

The older system is white rot. This is an enzyme-based attack on biomass — and if humans have been designing enzymes as a biomass conversion platform — white rot fungi is one of the reasons.

Now, most microorganisms use enzymes to break down compounds, but enzymes are huge molecules and physiologically “expensive” to produce because they contain so much nitrogen, said Barry Goodell, a professor at the University of Massachusetts Amherst.

Brown rot fungi appear in both the northern and southern hemispheres and are some of the most common decay fungi in North America.

“However, because of their efficiency in degrading wood,’ Goodell said, “brown rot fungi have come to dominate, particularly in degrading softwoods. They now dominate by recycling approximately 80 percent of the softwood biomass carbon in the world, found mostly in the great forests of the northern hemisphere.”

What’s new? Basidiomycota brown rot fungi, use a non-enzymatic, chelator-mediated biocatalysis method that is “very different than that used by any other microorganism studied,” he says. Chelators are organic compounds that bind metal ions, and in this case, they also generate “hydroxyl radicals” to break down wood and produce simple building-block chemicals.

“The fungi we study use a non-enzymatic, catalytic chelator-mediated Fenton system instead, a very simple process that makes use of hydrogen peroxide, also generated by the fungal system, and iron found in the environment.”

As Goodell explains, “This group of fungi evolved a way to break down the wood substrate by first diffusing chelators into the cell wall. The fungus makes the chelator and produces hydrogen peroxide from oxygen, and together they start to digest the cell wall into the sugar found in the basic building block of wood, glucose, which the fungus can use as food. This is how these fungi are eating the wood.” READ MORE Report