In addition to using isolated enzymes or
chemistries derived from brown rots, the
brown rot fungi alone or in consortia have
been used successfully to colonize biomass to
pretreat lignocellulose biomass (bagasse and
wood) to promote the release of sugars from
these materials in downstream processing (Ray
et al. 2010). The Mycologix LTD company
(CompaniesHouse.Gov.UK 2013) was technically successful in the pretreatment of biomass
in a commercial application, but rapid geopolitical changes resulting in decreases in the
price of fossil hydrocarbons caused the company to declare insolvency after 4 years of operation. Given the success of this process
however, as the economics for bioconversion
changes in the future, similar processes using
brown rot fungi may be developed for use in
bio-based platform chemical production.
Although the need for liquid fuels may lessen
as other forms of energy to power vehicles
increases in popularity, the need for bioconversion processes in the production of high-energy
density liquid fuels from lignocellulose in certain types of transit (long-range aerospace and
oceanic transport) will continue, and as the use
of fossil fuels inevitably dwindles, required pretreatments for biomass to produce this type of
commercial biofuel will likely increase. The use
of brown rot systems for this type of biomass
preparation in biorefineries may therefore find
application in the future.
V. Conclusions
This chapter has focused on fungi and fungal
systems that decay and degrade lignocellulose
materials. These fungi include the predominant
aerobic microorganisms on earth involved in
the depolymerization of cellulose and lignin.
Fungi reviewed include those that cause
brown rot, white rot, soft rot, stain and mold
of wood, and woody biomass. Most wooddegrading fungi possess extracellular enzymatic systems for the degradation of lignocellulose, but some of the more aggressive
degraders of lignocellulose, the brown rot
fungi, use a non-enzymatic CMF mechanism,
and perhaps other non-enzymatic mechanisms,
to depolymerize the components of the woody
cell walls. A more limited suite of CAZymes is
then subsequently secreted by the brown rot
fungi to permit further wood cell wall deconstruction. The white rot fungi deconstruct lignin primary via the use of lignin-degrading
enzymes, which in some cases require LMW
mediator compounds. Soft rot fungi are unique
in the manner in which they are capable of
tunneling into the wood cell wall and, in Type
I attack, produce a unique string of diamondshaped cavities that follows the microfibril
angle of the dominant wood cell wall layer.
Staining fungi have the ability to penetrate,
primarily into sapwood tissue, where they colonize parenchyma cells containing starches and
other readily digested substrates. The hyphae of
wood-staining fungi have the ability to pigment, resulting in the coloration of woody substrates.
Mold fungi generally do not penetrate into
wood cells deeply, and these fungi remain on
the surface of wood where they metabolize surface residues that may be deposited from external sources (wind and water deposits) or that
have diffused from deeper in the wood. Mold
fungi generally do not have colored hyphae, but
the mold spores can be darkly pigmented.
All the fungi discussed in this chapter have
the capacity to be used in biotechnological
applications. Only the Basidiomycota white rot
and brown rot biotechnology applications and
future potential are overviewed in this chapter,
as the Ascomycota applications are addressed
in other chapters of this book. Historical applications including the use of lignin-oxidizing
enzymes from white rot fungi, and their use in
biorefining and bio-pulping applications are
briefly reviewed. The potential of both classes
of fungi as well as their enzymes and the nonenzymatic CMF mechanism in brown rots is
discussed for biotech applications, including
their use in biorefineries, and pollutant/xenobiotic remediation.
15 Fungi Involved in the Biodeterioration and Bioconversion of Lignocellulose Substrates
391
chemistries derived from brown rots, the
brown rot fungi alone or in consortia have
been used successfully to colonize biomass to
pretreat lignocellulose biomass (bagasse and
wood) to promote the release of sugars from
these materials in downstream processing (Ray
et al. 2010). The Mycologix LTD company
(CompaniesHouse.Gov.UK 2013) was technically successful in the pretreatment of biomass
in a commercial application, but rapid geopolitical changes resulting in decreases in the
price of fossil hydrocarbons caused the company to declare insolvency after 4 years of operation. Given the success of this process
however, as the economics for bioconversion
changes in the future, similar processes using
brown rot fungi may be developed for use in
bio-based platform chemical production.
Although the need for liquid fuels may lessen
as other forms of energy to power vehicles
increases in popularity, the need for bioconversion processes in the production of high-energy
density liquid fuels from lignocellulose in certain types of transit (long-range aerospace and
oceanic transport) will continue, and as the use
of fossil fuels inevitably dwindles, required pretreatments for biomass to produce this type of
commercial biofuel will likely increase. The use
of brown rot systems for this type of biomass
preparation in biorefineries may therefore find
application in the future.
V. Conclusions
This chapter has focused on fungi and fungal
systems that decay and degrade lignocellulose
materials. These fungi include the predominant
aerobic microorganisms on earth involved in
the depolymerization of cellulose and lignin.
Fungi reviewed include those that cause
brown rot, white rot, soft rot, stain and mold
of wood, and woody biomass. Most wooddegrading fungi possess extracellular enzymatic systems for the degradation of lignocellulose, but some of the more aggressive
degraders of lignocellulose, the brown rot
fungi, use a non-enzymatic CMF mechanism,
and perhaps other non-enzymatic mechanisms,
to depolymerize the components of the woody
cell walls. A more limited suite of CAZymes is
then subsequently secreted by the brown rot
fungi to permit further wood cell wall deconstruction. The white rot fungi deconstruct lignin primary via the use of lignin-degrading
enzymes, which in some cases require LMW
mediator compounds. Soft rot fungi are unique
in the manner in which they are capable of
tunneling into the wood cell wall and, in Type
I attack, produce a unique string of diamondshaped cavities that follows the microfibril
angle of the dominant wood cell wall layer.
Staining fungi have the ability to penetrate,
primarily into sapwood tissue, where they colonize parenchyma cells containing starches and
other readily digested substrates. The hyphae of
wood-staining fungi have the ability to pigment, resulting in the coloration of woody substrates.
Mold fungi generally do not penetrate into
wood cells deeply, and these fungi remain on
the surface of wood where they metabolize surface residues that may be deposited from external sources (wind and water deposits) or that
have diffused from deeper in the wood. Mold
fungi generally do not have colored hyphae, but
the mold spores can be darkly pigmented.
All the fungi discussed in this chapter have
the capacity to be used in biotechnological
applications. Only the Basidiomycota white rot
and brown rot biotechnology applications and
future potential are overviewed in this chapter,
as the Ascomycota applications are addressed
in other chapters of this book. Historical applications including the use of lignin-oxidizing
enzymes from white rot fungi, and their use in
biorefining and bio-pulping applications are
briefly reviewed. The potential of both classes
of fungi as well as their enzymes and the nonenzymatic CMF mechanism in brown rots is
discussed for biotech applications, including
their use in biorefineries, and pollutant/xenobiotic remediation.
15 Fungi Involved in the Biodeterioration and Bioconversion of Lignocellulose Substrates
391