Biomedical Engineering Reference
In-Depth Information
are the main species for cellulose degradation. At present, the study of rumen micro-
bial cellulase has become a research focus for animal molecular nutrition. Microbes
in the rumen can degrade cellulose mainly because of the existence of fungi and
bacteria that can secrete cellulase, such as
Ruminococcus albus
,
Ruminococcus
flavefaciens,
and
Bacteroide succinogenes
[
1
]. The synergistic effects between
rumen microbes allow the rumen to be able to degrade cellulose well [
2
]. Therefore,
the rumen of ruminants is regarded as a natural fermentor and has aroused increasing
research interest.
According to the appearance in different stages of lignocellulose degradation, the
microbes can be divided into the following four categories:
1. The microbes appear rapidly in herbaceous plant leaves. This kind microor-
ganism can only use the secretions of leaves, the dung of insects and small
animals, and some compositions that are easy to decompose in the leaves, such as
starch and pectin. They have poor degradation ability on cellulose. The microbes
include
Cunninghamella
spp.,
Mortierella
spp.,
Muwor
spp.,
Aureobasidium
spp.,
Cladosporium
spp.,
Epicoccum
spp., and so on. Some of them grow on
the leaves before they fall, and others grow in soils. They seldom appear in
the end of lignocellulose degradation. The use of
Muwor
spp. fungi in the
biodegradation of lignocellulose depends mainly on their fast growth and strong
proliferation ability, which can make them occupy resources quickly before
other microbes. However, they will disappear soon with the gradual reduction
of available nutrients and the invasion of other microbes.
2. The microbes appear in the early and middle stages of the degradation process,
including genera of
Chaetomium
spp. and
Deuteromycota
spp., which can grow
on cellulose and hemicelluloses.
3. Microbes are almost not detectable in the early stage of the degradation
process; these mainly include lignin-degradable Basidiomycota
,
such as
Mycena
spp.,
Marasmius
spp.,
Lepiota
spp.,
Collybia
spp., and so on. They have a
strong ability in the utilization of complex organic compounds, low population
densities, and high stability. Many actinomycetes and Basidiomycota, which
are typical representatives, can grow and reproduce stably in environments
composed mainly of lignin, chitin, and humus.
4. The microbes that can be detected during the entire process of lignocellulose
degradation include
Cladosporium
spp.,
Trichoclerma
spp.,
Penicillium
spp.,
Aspergillus
spp., and others. Some yeast, bacteria, and actinomycetes also
participate in the entire process of degradation of fallen leaves.
According to the degradation differences on lignocellulose components, the
microbes can be divided into the following three categories:
1. Cellulose-degradable microorganisms, which include fungi, actinomycetes, bac-
teria, protozoa, and so on. The decomposition ability of fungi is especially
strong, including some ascomycetes, adelomycetes, and basidiomycetes. Some
cellulose-degradable microorganisms include strains from
Polyporus
spp.,
Agar-
icales
spp.,
Trichoderma
spp., and
Myrothecium
spp.; also included are
Sporocy-
tophaga myxococcoides, Streptomyces antibioticus
, and so on.
