Wood digestion without enzymes

SUCCESSFULLY understanding the unique, non-enzymatic digestion of wood by a fungus has been described by researchers as “a paradigm shift in understanding fungal biocatalysis for biomass conversion.”

This claim was made by researchers at Oak Ridge National Laboratory, US, who were part of an international collaboration to describe the mechanism used by ‘brown rot fungi’ to digest and recycle wood.

Brown rot fungi appear in both the northern and southern hemispheres, and are some of the most common degrading organisms in conifer-rich forests. Their efficiency in decaying wood, especially softwood, means they recycle approximately 80% of the softwood biomass carbon in the world.

How the fungi do this has been described for the first time by a group of researchers from the US, China, Sweden and Japan. They believe that the mechanism used to degrade wood is very different to any other organism studied, and could offer a new alternative in industrial bioprocessing.

Lead researcher Barry Goodell, from the US’ University of Massachusetts Amherst, said: "Our research on fungal bioconversion systems looks at a novel mechanism that has potential use in bio-refineries to 'deconstruct' woody biomass for conversion into platform chemicals for biopolymers or energy products.”

The group found that the fungus uses a non-enzymatic, catalytic chelator-mediated Fenton (CMF) system to digest wood. This simple process makes use of hydrogen peroxide also generated by the fungal system, and iron found in the environment.

Goodell said: “By its nature, the (CMF) system uses bio-based chemistries that also are fairly benign in the environment. Developing a process to digest biomass to ultimately produce bio-based products and energy would be safe, and could potentially save large amounts of energy because the fungi run the process at ambient temperatures.

To simulate the CMF on biomass in the lab, we also typically run it at low temperatures. Although the chemistry is simple, it does require a detailed understanding of how the fungi work in order to run it in the lab as efficiently as the fungi seem to do."

The researchers have previously been able to achieve 77% solubilisation of softwood with the CMF system – which is notable as softwoods are generally considered to be more difficult to process in biorefineries than hardwoods or grasses.

Products from the process include modified lignin, which can be a feedstock for various bioplastics or a substitute for phenolic resins, for example. A sugar stream is also produced, and there are a variety of organisms that can ferment sugars to 'platform chemicals' that can be used to produce biopolymers – sugars can also be fermented to fuels if desired.

Goodell said: "More research is needed on these conversion phases, but right now we are working hard to improve the conditions for future scale-up just of the CMF system to produce the raw sugars and modified lignin. The CMF system is quite robust, and does not require the careful control of system conditions that are needed with enzymes. So there may be some advantages of using the CMF for the bulk of the biomass digestion, with enzymes then being used to digest the smaller molecular fragments to sugars.

"Colleagues in Norway have already reached out to support a current collaborative research grant based on CMF technology in synergy with enzymatic action. We would of course like to see similar research efforts supported in the US, and we are always looking for grant and collaborative opportunities to make that happen."

Biotechnology for biofuels: http://doi.org/b9xg