Biomedical Engineering Reference
In-Depth Information
3.1.1.5
Filamentous Fungi
Fungi play an important role in the decomposition of lignocellulose; they can
generally be divided into mesophilic fungi and thermophilic fungi. Most mesophilic
fungi grow well at 5-37
ı
C, with an optimum temperature range of 25-30
ı
C.
Thermophilic fungi have strong decomposing ability on cellulose, hemicellulose,
and lignin. They can secrete extracellular enzymes, and their mycelia have the func-
tion of mechanical interpenetration; these two things combine to degrade refractory
organics (such as cellulose and lignin) and promote biochemical reactions [
11
].
Filamentous fungi are idiomatic expressions, which refers to the mycelia group
of low fungi growing on solid media. It is easy to obtain a pure culture for
such cellulose fungi; they have simple nutritional requirements, exist in vari-
ous ecological environments, and have high extracellular cellulase activity. The
understanding of the mechanisms of enzymatic degradation of cellulose started
from this type microbe. They mainly include
Sclerotium rolfsii
,
Phanerochaete
chrysosporium
,
Trichoderma
spp.,
Aspergillus
spp.,
Schizophyllum
spp.,
Penicillium
spp., and so on. Among them,
Trichoderma
spp. are the most extensively studied
cellulase-producing microbes, and 20 % of commercial cellulase is produced from
Trichoderma
spp. and
Aspergillus
spp. [
12
,
13
].
Trichoderma
spp.,
Penicillium
spp.,
Myrothecium
spp.,
Chaefomium
spp.,
Neurospora
spp., and others can pro-
duce extracellular cellulase with high filter paper activity; cellulase produced by
Aspergillus
spp. and
Rijopus
spp. have low
-glucan enzyme activities [
5
,
11
].
Basidiomycetes play an important role in the biodegradation of lignocellulose.
These fungi can be divided into three categories: brown-rot fungus, white-rot
fungus, and soft-rot fungus. Brown-rot fungi, including
Coniphora puteana
and
Trichoderma viride,
mainly decompose cellulose and hemicellulose components,
having almost no effect on lignin. White-rot fungus, including
Poria subacida
,
Polyporus versicolor
, and
Pleurotus ostreatus,
acts first on lignin and scarcely
degrades fiber polysaccharides. Soft-rot fungus (e.g.,
Cheatomium globosum
) can
degrade both cellulose and lignin in hardwood and softwood, but the degradation
rate is slow [
11
].
Trichoderma
spp. and
Penicillium
spp. are suitable strains for producing cellu-
lase; when they grow on the surface of lignocelluloses, their degradation effect is
carried out by the secreted cellulase, not by the penetration of mycelia into the cell
wall of fiber material. The mycelia of
Chaetomium
sp.,
Ceratocystis sensu lato,
and
Xylaria
sp. can penetrate into the cell wall of lignocellulosic materials and degrade
them more thoroughly. Their extracellular enzyme activity is low, so they are not
suitable for the production of cellulase; they are suitable for the production of feeds
by converting lignocellulosic materials into protein. Plant pathogenic fungi such
as powdery mildew, anthrax, and
Cladosporium
are immersed in the plant tissue
during the period of plant growth. They all have pectinase activity and endocellulose
activity.
Chaetomium thermophile, Sporotrichum thermophile
, and
Thermonascm
aurantiacus
, which are isolated from compost, can decompose cotton, filter paper,
and other items efficiently at 50
ı
C, but their extracellular cellulase activity is not
high [
5
].
“
