Fungal staining in structural lumber and
wood products is allowed in many countries as
no change in modulus of rupture or modulus
of elasticity occurs in this wood. However,
some wood products specifically exclude fungal stained wood. Also, international shipments of wood with fungal stain (and mold)
have been limited in some cases (NeLMA 2016;
FAO 2016). High-temperature kiln drying of
wood can kill the fungi, and for some
countries, this is a permissible solution if
international shipment of wood with fungal
stain is a concern. Fungal stain is also a concern in certain wood products that may
undergo shock loading as is the case in ladder
stock where a misplaced foot, when ascending
or descending, may result in a rapid loading of
the step below. The removal of hemicellulose
in heavily stained wood causes loss of toughness or shock resistance by as much as 15–30%
(Forest-Products-Laboratory 2010) and hence,
this wood is not allowed by code in structural
applications that may experience shock loading or that require toughness.
IV. Biotechnological Applications of
Decay Fungi
A. White Rot Fungi
As noted earlier in this chapter, the term “white
rot fungi” refers to a group of organisms which
attack all of the major wood constituents, primarily via enzymatic action. Often white-rotted
wood, especially in late stages of decay, is characterized by residual wood material which
appears bleached. In some common types of
white rot decay, the wood will become soft
and develop a “stringy” character where the
softened wood fibers can be easily separated
allowing the wood to be peeled apart. In other
types of white rot, pockets of softened, deteriorated zones of wood may appear. Like all wooddegrading fungi, white rot fungi require oxygen, water, and a suitable wood substrate for
growth. In general, the preferred substrates for
white rot fungi are hardwood species or bamboo. Compared to brown rot attack, enhanced
growth with corresponding greater mass loss
will typically occur when hardwoods are inoculated with white rot fungi because these fungi
have the ability to metabolize lignin rather than
just depolymerizing and modifying lignin as
occurs in the brown rots.
White-rotted wood has historically been
used for a variety of applications, ranging
from insulated paneling in Russian refrigerator
trucks/vehicles to cattle feed. In the later application, the selective white rot fungi free the
cellulose from the lignin fraction of the wood
or fiber, improving the digestibility in ruminant
animals. White-rotted wood that has been naturally decayed by Ganoderma spp. in southern
Chile has been used as food by indigenous
peoples and as cattle feed for centuries (Dill
and Kraepelin 1986). Biotechnological and
biorefinery applications of white rot fungi
have been explored for more than 30 years
(Blanchette et al. 1988; Wolfaardt et al. 2004;
Eriksson and Kirk 1985) with the initial focus
being to free cellulose from lignin to enhance
“biopulping” prospects. Composite wood products have also been bonded together by using
lignin, and the lignin on the surface of wood
fibers, after activation by white rot fungal
enzymes including laccase and peroxidase
enzymes (Widsten and Kandelbauer 2008),
with laccase enhancement through the use of
mediators. White rot fungi also have a long
history of testing for use in applications in the
remediation of pollutants and xenobiotics (Barr
and Aust 1994; Magan et al. 2010), at least in
aerobic environments with adequate moisture
for fungal growth.
More recently, interest in biorefineries and
the production of cellulose-derived sugars for
fermentation and direct conversion to biofuels
and platform chemicals has been a targeted use
for white rot fungi. Proposed uses for selective
white rot fungi include using their potential for
selective delignification of biomass in biotechnological applications including biorefineries
(Dashtban et al. 2010; Baba et al. 2011). In this
regard, white rot species including Ceriporiopsis subvermispora, Phlebia subserialis, Dichomitus squalens, Pycnoporus cinnabarinus, and
many others now have been tested for potential
use in biorefinery applications (Capolupo and
15 Fungi Involved in the Biodeterioration and Bioconversion of Lignocellulose Substrates
389
wood products is allowed in many countries as
no change in modulus of rupture or modulus
of elasticity occurs in this wood. However,
some wood products specifically exclude fungal stained wood. Also, international shipments of wood with fungal stain (and mold)
have been limited in some cases (NeLMA 2016;
FAO 2016). High-temperature kiln drying of
wood can kill the fungi, and for some
countries, this is a permissible solution if
international shipment of wood with fungal
stain is a concern. Fungal stain is also a concern in certain wood products that may
undergo shock loading as is the case in ladder
stock where a misplaced foot, when ascending
or descending, may result in a rapid loading of
the step below. The removal of hemicellulose
in heavily stained wood causes loss of toughness or shock resistance by as much as 15–30%
(Forest-Products-Laboratory 2010) and hence,
this wood is not allowed by code in structural
applications that may experience shock loading or that require toughness.
IV. Biotechnological Applications of
Decay Fungi
A. White Rot Fungi
As noted earlier in this chapter, the term “white
rot fungi” refers to a group of organisms which
attack all of the major wood constituents, primarily via enzymatic action. Often white-rotted
wood, especially in late stages of decay, is characterized by residual wood material which
appears bleached. In some common types of
white rot decay, the wood will become soft
and develop a “stringy” character where the
softened wood fibers can be easily separated
allowing the wood to be peeled apart. In other
types of white rot, pockets of softened, deteriorated zones of wood may appear. Like all wooddegrading fungi, white rot fungi require oxygen, water, and a suitable wood substrate for
growth. In general, the preferred substrates for
white rot fungi are hardwood species or bamboo. Compared to brown rot attack, enhanced
growth with corresponding greater mass loss
will typically occur when hardwoods are inoculated with white rot fungi because these fungi
have the ability to metabolize lignin rather than
just depolymerizing and modifying lignin as
occurs in the brown rots.
White-rotted wood has historically been
used for a variety of applications, ranging
from insulated paneling in Russian refrigerator
trucks/vehicles to cattle feed. In the later application, the selective white rot fungi free the
cellulose from the lignin fraction of the wood
or fiber, improving the digestibility in ruminant
animals. White-rotted wood that has been naturally decayed by Ganoderma spp. in southern
Chile has been used as food by indigenous
peoples and as cattle feed for centuries (Dill
and Kraepelin 1986). Biotechnological and
biorefinery applications of white rot fungi
have been explored for more than 30 years
(Blanchette et al. 1988; Wolfaardt et al. 2004;
Eriksson and Kirk 1985) with the initial focus
being to free cellulose from lignin to enhance
“biopulping” prospects. Composite wood products have also been bonded together by using
lignin, and the lignin on the surface of wood
fibers, after activation by white rot fungal
enzymes including laccase and peroxidase
enzymes (Widsten and Kandelbauer 2008),
with laccase enhancement through the use of
mediators. White rot fungi also have a long
history of testing for use in applications in the
remediation of pollutants and xenobiotics (Barr
and Aust 1994; Magan et al. 2010), at least in
aerobic environments with adequate moisture
for fungal growth.
More recently, interest in biorefineries and
the production of cellulose-derived sugars for
fermentation and direct conversion to biofuels
and platform chemicals has been a targeted use
for white rot fungi. Proposed uses for selective
white rot fungi include using their potential for
selective delignification of biomass in biotechnological applications including biorefineries
(Dashtban et al. 2010; Baba et al. 2011). In this
regard, white rot species including Ceriporiopsis subvermispora, Phlebia subserialis, Dichomitus squalens, Pycnoporus cinnabarinus, and
many others now have been tested for potential
use in biorefinery applications (Capolupo and
15 Fungi Involved in the Biodeterioration and Bioconversion of Lignocellulose Substrates
389