*8.2. Brown Rot Fungi*

Brown rot fungi have received less study for biotechnological applications, primarily because their ability to rapidly depolymerize the carbohydrate fraction of the wood was viewed as having little practical application. However, more recent studies indicate that some CAZymes, such as lytic polysaccharide monooxygenases (LMPOs), have the ability to work synergistically with peroxidases to promote depolymerization and solubilization of aromatic monomers from lignin [37,58]. These results suggest that cellulase enzymes from either white or brown rot fungi could play a greater role in lignin depolymerization for use as a chemical feedstock. CAZymes from brown rot fungi have not been explored to a great extent largely because they are less common compared to white rot fungi. LPMO enzymes from brown rot fungi have only been isolated within the last five years, and have not been fully explored for use in industrial applications. Preliminary reports suggest that an LMPO from the brown rot fungus *Gloeophyllum* spp. cloned into yeast has significant potential for biorefinery applications [37,59]. Studies have tended to look for one or a few mechanisms of action, but it may be

necessary to change the paradigm by combining enzymatic and non-enzymatic mechanisms under controlled conditions to either modify fibers or create platform chemicals [38].

The non-enzymatic activity of brown rot fungi has previously been shown to activate lignin for production of laminated wood [60] and composite panels [61]. Brown rotted lignin modified with a sodium borohydride treatment was previously used to produce a formaldehyde-free adhesive resin with properties close to that of phenolic resins [62]. The CMF mechanism from fungal systems has been used to activate lignin on fiber surfaces for the producing fiber-based products at an experimental level and has been shown to have potential industrial applications [63–66]. Lignin has also been modified using a CMF system to produce water-soluble polymers that have potential applications as a high-value dispersant comparable to poly(acrylic) acid [67].

Brown rot fungi have also been explored for bioremediation, especially for removal of copper and other heavy metals. *Serpula* spp. has been shown to remove copper from preservative-treated wood [68]. CMF chemistry also has effectively degraded pollutants like 2,4-dichlorophenol [69], dichloro-diphenyl-trichloroethane (DDT) [70] and pentachlorophenol [71] as well as decolorizing recalcitrant dyes [72,73]. An improved understanding of brown rot mechanisms over the past 20 years has encouraged a re-examination of using these fungi in bioremediation.

Brown rot fungi have also successfully been used to pretreat bagasse, wood and other lignocellulose substrates to promote cellulose and hemicellulose depolymerization for biorefinery applications [74]. The Mycologix LTD company [75] successfully pretreated biomass in a commercial application, but dramatic decreases in the cost of competing fossil hydrocarbons led the company to declare corporate insolvency. The initial success of this process suggests that similar efforts will emerge as the economies of the process improve and hydrocarbon prices rise. While the need for biofuels may be somewhat mitigated by the emergence of other renewable energy sources, liquid fuels will continue to be required in many industries. The use of brown rot systems for biomass preparation in biorefineries will likely increase, and markets for the lignin residues produced in these processes will be needed, creating opportunities for developing lignin-based coatings as well as polymeric resins.
