ABSTRACT
An endo-β-1, 4-glucanase (EC. 3.2.1.4) from a Neurospora
sp isolated from a mouldy corn cob was produced in a solid substrate
fermentation (SSF) system of 30.2% moisture level. The enzyme was optimally
produced in 48h at an initial culture pH of 6.0 in a medium consisting of corn
cob, 5g; defatted melon meal, 1g; MnS04.H20, 2.5mM and sodium dodecyl
sulphate (SDS), 0.16%. The relative rates of hydrolysis of
carboxymethyl-cellulose, crystalline cellulose and crude lignocellulosic wastes
by the crude enzyme extract showed the preference of the enzyme to carboxymethyl-cellulose.
The least hydrolyzed cellulose was sigmacel.
CHAPTER ONE
INTRODUCTION
Cellulose is the most abundant
renewable natural organic resource found in plants, some micro-organisms, and
industrial and agricultural residues. Pure cellulose does not occur in nature
but is always associated with varying amounts of a variety of non-cellulosic
materials especially hemicellulose and lignin (Lutzen et al., 1983).
Cellulose is a high molecular
weight linear polymer containing glucose molecules linked by β-1, 4-glycosidic
bonds. It is degraded by a complex of three enzymes called cellulases. These
are:
Cellobiohydrolase or exoglucanase
or exo-1,4-β-glucan cellobiohydrolase (EC. 3.2. 1.91)
Endo-β-glucanase, also called
endoglucanase or endo-1, 4-β-D-glucan 4-glucanohydrolase (EC.3.2.1.4)
Cellobiase or β-glucosidase (EC.
3.2.1.21)
The endo-β-glucanase is an
endo-enzyme that attacks cellulose polymers randomly resulting in rapid
reduction in chain length and increase in reducing groups and reduction in viscosity.
The cellobiase (β-glucosidase),
however, does not attack cellulose but rather the cello-oligosaccharides and
cellobiose which inhibit the activities of cellobiohydrolase and
endo-β-glucanase. Thus its presence is essential in the complete hydrolysis of
cellulose (Halliwell, 1979). Plant biomass and agricultural wastes are in
abundance, especially in the tropical savannah and rainforest zones of Africa.
Of fundamental importance is the fact that many chemicals and materials must be
produced from plant biomass once petroleum, natural gas and coal are no longer
affordable or acceptable for use in view of their role in climate change (van
Beihen,2008).
Cellulose degradation in nature
ensures the maintenance of the carbon cycle and energy transfer among living
systems. Without it, dead vegetations would pile up and suppress the formation
of new ones causing the atmospheric carbon dioxide pool not to be consumed by
photosynthesis (Demain et al., 2005).
Microbial degradation of cellulose
has the potential of providing food and energy. For instance, the glucose
resulting from cellulose degradation can be fermentatively converted to ethanol
and butanol (biofuels), acetone, isopropanol, and biomass in form of single
cell protein. In this way, they serve in the production of value-added goods as
well as serving as effective means of disposal of such wastes (Sauer, 2008).
Cellulose is degraded by a large
number of organisms including the fungi, actinomycetes, myxobacteria and the
true bacteria. Most research on cellulase – producing microorganisms has
involved fungi’
Neurospora is a perfect ascomycete
that is most thoroughly characterized genetically and produces a complete set
of cellulases. It is argued that Neurospora is a most favourable organism for
the degradation of hemicellulose. For instance, Deshphande et al.(1986)
reported the direct conversion of hemicellulose and cellulose to ethanol by Neurospora
and Phadtare et al.(1997) reported of Neurospora’s unique ability to convert
biomass to ethanol.
Neurospora is peculiarly
non-pathogenic, perhaps because it normally has the luxury of growing in a fire
scoured landscape, without competitors. So far, no infection or intoxication by
Neurospora has ever been reported in human beings, including immune compromised
people, or in any live animal or plant (Zhao et al., 1998).
Neurospora is closely related to
several industrially important organisms such as Hypocrea jecorina. It is
widely consumed as a foodstuff in parts of southeast Asia as the microbial
agent in a cultured pressed peanut or soybean cake called “oncham” (The Scientist, 1996). There are reports
on the production of cellulase degrading enzymes by species of Neurospora (
Oguntimien et al., 1991).
These studies were carried out by
submerged fermentation, a process which is cost-intensive and requires strict
asepsis.
In order to reduce the cost of
cellulase production, this study aimed at :
i. Optimizing the cultural conditions
for endo-β-glucanase production by a Neurospora sp in a solid substrate
fermentation (SSF) system, and
ii. studying the kinetics of the
degradation of some cellulosic wastes using the crude endo-β-glucanase.
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