Biomedical Engineering Reference
In-Depth Information
Currently, cellulase is derived commercially from filamentous fungi. For exam-
ple, Cellulase-Onojuka, Cellulosin AC, Macerojume, and Toyo-cellulose are gen-
erated by
Trichoderma viride
,
Aspergillus niger
,
Rhizopus arrhizus
, and
Fusarium
moniliforme
, respectively.
Filamentous fungi generally can degrade cellulose and hemicelluloses but not
lignin. Degradation of lignin in nature is mainly by white-rot fungi. The majority of
white-rot fungi can degrade both hardwood and softwood. They have more speed
and efficiency than other strains for degrading lignin. Lignin-degradable white-
rot fungi include
Phanerochaete chrysosporium
,
Trametes versicolor
,
Pleurotus
ostreatus,
and
Pycnoporus
spp. [
11
]. But, they grow slowly. Although they can
strongly degrade cellulose, extracellular cellulase activity is low, which is almost
undetectable with the traditional enzyme activity detection method. They generally
do not produce asexual spores and can only rely on the mycelial breeding, which
makes it difficult to scale up cultivation. They have a low propagation coefficient
and a long culture period.
However, among the current commercial cellulases, there are at least two
enzymes from basidiomycetes. One is driselase, produced by
Irpex lacteus
; another
is Cellulase A-12-C, produced by
Trametes sanguinea
. Therefore, the basid-
iomycetes are also important as breeding strains for industrial production [
3
].
In short, the types of microorganisms that can synthesize complete cellulase com-
ponents and secrete extracellularly to degrade cellulose are limited. Many species
of bacteria, actinomycetes, and basidiomycetes can grow on natural lignocellulose
or have a strong ability to decompose lignocellulose, but the extracellular cellulase
activity is usually low. For example, the cellulase from myxobacteria is a surficial
enzyme that binds to the surface of cells and decomposes cellulose when the bacteria
contact cellulose [
3
].
3.1.2
Hemicellulose-Degradable Microorganisms
Almost all known majority of cellulose-degradable filamentous fungi can decom-
pose hemicellulose and have high extracellular hemicellulase activity. However,
hemicellulose-degradable microorganisms do not necessarily have the ability to
decompose cellulose. In addition, some well-known amylase-producing bacteria
often have a hemicellulose decomposition ability. Because hemicellulose is a
generic name for a group of copolymers, the decomposition of such substances
requires a variety of enzymes and microbes. Now, the hemicelluloses are classified
according to different types of sugar residues contained in the main chain.
(1) Poly-L-arabinose
In the 1960s, it was found that bacillus, tumor endophytic fungus, plant pathogenic
fungi, rumen bacteria, protozoa, and others could degrade poly-L-arabinose. Typ-
ical microorganisms include
Butyrivibrio fibrisolvens
,
Clostridium felsineum,
and
Aspergillus niger
.
