Biomedical Engineering Reference
In-Depth Information
2. Hemicellulose-degradable microorganisms. In this type of microbe, fungi domi-
nate at the early stage of the degradation of hemicellulose, but actinomycetes are
dominant at the later stage. Many groups of fungi can decompose hemicellulose;
their number is much greater than that for cellulose degradation.
3. Lignin-degradable microorganisms. These mainly are Basidiomycota and
Aphyl-
lophorales
spp. fungi, such as
Fo m e s
spp.,
Polyporus
spp.,
Polystictus
spp., and
so on.
3.1.1
Cellulose-Degradable Microorganisms
In nature, only cotton fibers and a few other lignocellulosic materials are composed
of single-cellulose molecules. Most of the natural lignocellulosic materials are a
mixture of cellulose, hemicellulose, lignin, and other materials. The degradation
lignocellulose by microbes is complex. Some microbes have complete cellulolytic
enzymes and can degrade three components of lignocellulose. Some of the microbes
can only degrade one of them; some only participate in a single reaction process.
Cellulose-degradable microorganisms are a type of physiodeme with degrading abil-
ity on natural lignocellulose and do not include the microbes that can only degrade
the degradation products of natural lignocellulose and water-soluble cellulose,
although they also have an important role in the process of cellulose degradation.
Cellulose-degradable microorganisms include different groups of bacteria, actino-
mycetes, and fungi [
3
].
3.1.1.1
Mesophilic Aerobic Bacteria
Aerobic bacteria play a significant role in the rapid degradation of cellulose in
the surface of neutral and slightly alkaline soil. They can effectively degrade
the unlignified lignocellulose, such as twigs and cotton, but it is difficult for
them to degrade lignified lignocellulose. The excreted cellulolytic enzymes of
aerobic bacteria adhere to the cell wall and cell membrane. These enzymes are not
extracellular enzymes with low activity and are difficult to detect unless the cells are
broken down.
Cytophaga
spp. and
Sporocytophaga
spp. are aerobic cellulose-degradable bac-
teria commonly existing in soil. When they grow on filter paper, the surface of
the filter paper appears pale yellow or other colors colonies. Macroscopically,
filter paper dissolves and is attenuated in the area where colonies have grown. By
observation with an optical microscope, it can be found that the bacteria in the
colonies of various developmental stages exhibit different morphologies. In the early
growth of bacteria, the cells bend, and two ends are sharp; later, the cells become
shorter and thicker, and the cells arch just like
Cytophaga
spp. Some bacteria, such
as
Sporocytophaga
spp., can form small cysts and produce heat-resistant spores [
4
].
