rot mechanisms; however, with the reduction in
CAZyme complement including LPMO and
endoglucanases in brown rots, the nonenzymatic systems clearly take on a priority
role in the brown rot fungi.
More study is needed to understand
whether interactions between enzymes and
metabolomic compounds are important in
brown rot degradation, for example, if some of
the LMW compounds produced by the fungi are
important as electron donors for some enzymes
like LPMOs. It has been reported that lignin
derivatives produced during brown rot degradation are active in multiple iron reduction, and
it is proposed that these compounds also function as electron donors for enzymes such as
LPMOs (Tamaru et al. 2019; Westereng et al.
2015; Frommhagen et al. 2017). Understanding
whether temporal staging in expression of LMW
metabolites and extracellular enzymes is important requires further study. Currently, it is
unclear if staging of non-enzymatic and enzymatic systems is required to protect extracellular enzymes from non-enzymatic radical
generating systems or if generation of the nonenzymatic radicals within the wood cell wall
where enzymes have no accessibility allows adequate protection of extracellular enzymes.
Brown rot fungi may have additional mechanisms that have yet to be discovered, but certainly, the use of dual mechanisms (both
spatial separation and temporal expression
staging) to protect critical enzymes is possible.
3. Dry Rot
“Dry rot” is a colloquial term that has been used
to describe a particular brown rot decay type
caused by the genus Serpula with some validity,
as this genus has the ability to channel water
from several meters away to the site of active
decay. Therefore, although the wood still
requires water to decay the wood, the requirement that the wood be wet before decay initiation does not hold with this type of brown rot
fungus. Serpula lacrymans is common in Europe and Asia, whereas Serpula (Meruliporia)
incrassata is the most common of the dry rot
species in North America (Boddy 2016). Serpula dry rots are true brown rot fungi, but
their unique ability to channel water from
sources at a distance from the wood being
infected is permitted by an elongated hyphal
mass known as a rhizomorph structure. Multiple rhizomorphs are often present and have
been reported to extend as much as 10 m from
the site of decay to reach sources of water.
Interior decay of secondary wood structures
with fungal rhizomorphs extending to wet soil
sites exterior to the structure have been personally observed by the author.
The term “dry rot” is also sometimes used by laypersons as a misnomer, particularly in North America, to
describe brown-rotted wood caused by genera other
than Serpula. In these cases, the wood has been decayed
by a brown rot fungus in a wetted state, and it has the
appearance of brown crumbly wood in the dry state.
The term may be incorrectly used in this way by laypersons observing wood that has been wetted at some
point in its history, and decay had initiated and progressed to an advanced state before water was removed
and the wood dried out, but it is not an accepted use by
professionals in the field. As discussed generally for
fungi that attack wood, the presence of an adequate
amount of water, in amounts greater than the fiber
saturation point (FSP) of the wood, is necessary for all
types of fungal degradation to occur. Brown rot decay
cannot proceed in the absence of water.
C. White Rot Fungi
Additional background information on white
rot degradation of wood and the properties of
white-rotted wood can also be found in Sect. IV
of this chapter on biotechnological applications
of wood degrading fungi. White rots are classified in different ways, but the most common is
to physically classify the fungus by the appearance of the decayed wood. Two distinct types of
white rot from this macroscopic perspective are
(a) decayed wood that appears whitish or
bleached in a uniform manner and is variously
known as “spongy white rot,” “stringy white
rot,” or because it is the most common type,
just “white rot” (Fig. 15.4a) and (b) decayed
wood that is variously known as “pocket white
15 Fungi Involved in the Biodeterioration and Bioconversion of Lignocellulose Substrates
379
CAZyme complement including LPMO and
endoglucanases in brown rots, the nonenzymatic systems clearly take on a priority
role in the brown rot fungi.
More study is needed to understand
whether interactions between enzymes and
metabolomic compounds are important in
brown rot degradation, for example, if some of
the LMW compounds produced by the fungi are
important as electron donors for some enzymes
like LPMOs. It has been reported that lignin
derivatives produced during brown rot degradation are active in multiple iron reduction, and
it is proposed that these compounds also function as electron donors for enzymes such as
LPMOs (Tamaru et al. 2019; Westereng et al.
2015; Frommhagen et al. 2017). Understanding
whether temporal staging in expression of LMW
metabolites and extracellular enzymes is important requires further study. Currently, it is
unclear if staging of non-enzymatic and enzymatic systems is required to protect extracellular enzymes from non-enzymatic radical
generating systems or if generation of the nonenzymatic radicals within the wood cell wall
where enzymes have no accessibility allows adequate protection of extracellular enzymes.
Brown rot fungi may have additional mechanisms that have yet to be discovered, but certainly, the use of dual mechanisms (both
spatial separation and temporal expression
staging) to protect critical enzymes is possible.
3. Dry Rot
“Dry rot” is a colloquial term that has been used
to describe a particular brown rot decay type
caused by the genus Serpula with some validity,
as this genus has the ability to channel water
from several meters away to the site of active
decay. Therefore, although the wood still
requires water to decay the wood, the requirement that the wood be wet before decay initiation does not hold with this type of brown rot
fungus. Serpula lacrymans is common in Europe and Asia, whereas Serpula (Meruliporia)
incrassata is the most common of the dry rot
species in North America (Boddy 2016). Serpula dry rots are true brown rot fungi, but
their unique ability to channel water from
sources at a distance from the wood being
infected is permitted by an elongated hyphal
mass known as a rhizomorph structure. Multiple rhizomorphs are often present and have
been reported to extend as much as 10 m from
the site of decay to reach sources of water.
Interior decay of secondary wood structures
with fungal rhizomorphs extending to wet soil
sites exterior to the structure have been personally observed by the author.
The term “dry rot” is also sometimes used by laypersons as a misnomer, particularly in North America, to
describe brown-rotted wood caused by genera other
than Serpula. In these cases, the wood has been decayed
by a brown rot fungus in a wetted state, and it has the
appearance of brown crumbly wood in the dry state.
The term may be incorrectly used in this way by laypersons observing wood that has been wetted at some
point in its history, and decay had initiated and progressed to an advanced state before water was removed
and the wood dried out, but it is not an accepted use by
professionals in the field. As discussed generally for
fungi that attack wood, the presence of an adequate
amount of water, in amounts greater than the fiber
saturation point (FSP) of the wood, is necessary for all
types of fungal degradation to occur. Brown rot decay
cannot proceed in the absence of water.
C. White Rot Fungi
Additional background information on white
rot degradation of wood and the properties of
white-rotted wood can also be found in Sect. IV
of this chapter on biotechnological applications
of wood degrading fungi. White rots are classified in different ways, but the most common is
to physically classify the fungus by the appearance of the decayed wood. Two distinct types of
white rot from this macroscopic perspective are
(a) decayed wood that appears whitish or
bleached in a uniform manner and is variously
known as “spongy white rot,” “stringy white
rot,” or because it is the most common type,
just “white rot” (Fig. 15.4a) and (b) decayed
wood that is variously known as “pocket white
15 Fungi Involved in the Biodeterioration and Bioconversion of Lignocellulose Substrates
379