Current Trends in Research and Application of Microbial Cellulases
Bioconversion of cellulose, natures most abundant polysaccharide is accomplished by the enzyme cellulase. Cellulase, a complex of sequentially acting component enzymes are found to be synthesized by a variety of microbes. A number of different catalytic and non catalytic enzyme modules form the cellulase which synergistically acts on their substrates are reported, amongst which in some anaerobic bacteria different cellulases are organized together to form a multifunctional supramolecular complex known as cellulosome. Basic and applied research on microbial cellulases generated great scientific knowledge, their mode of action and their enormous industrial applications. Microbial cellulases are used in food, animal feed, brewery, wine, textile, laundry, paper, pulp and agriculture as well as in research purposes. The ever increasing demand for relatively non expensive cellulases and their enhanced utilization in multiple sectors of industries is the main driving force for research on different microbial cellulases.
Received: March 18, 2010;
Accepted: April 26, 2010;
Published: August 18, 2010
Cellulose rich plant biomass is one of the foreseeable and sustainable source
of fuel, animal feed and feed stock for chemical synthesis (Bhat,
2000). Therefore the conversion of cellulosic biomass to fermentable sugars
and alcohols through biocatalyst cellulase produced by various cellulolytic
organisms has attracted a world wide attention (Ladisch
et al., 1983). Complete enzymatic hydrolysis of cellulose requires
synergistic action of three cellulase enzymes: endoglucanase, exoglucanase and
beta-glucosidases (Ryu and Mandels, 1980). Extensive
basic and applied research on cellulases revealed their commercial significance
and industrial applicability (Bajpai, 1999; Bayer
et al., 1994; Beguin and Aubert, 1994; Bhat
and Bhat, 1997; Gilbert and Hazlewood, 1993; Godfrey
and West, 1996; Harman and Kubicek, 1998; Poutanen,
1997; Saddler, 1993; Uhlig, 1998).
In spite of their commercial importance, the high cost of production of these
enzymes has hindered the industrial application of cellulose bioconversion (Narasimha
et al., 2006) therefore, there is an ever increasing demand for more
stable, highly active, specific enzymes of nominal cost. In order to increase
the production and applicability of microbial cellulase, various biotechnological
approaches were adopted by the scientists. Biotechnology of cellulases began
in early 1980s, first in animal feed followed by food applications (Voragen,
1992) later in the textile, laundry as well as in the pulp and paper industries
(Godfrey and West, 1996). During the last two decades,
the use of cellulases has increased considerably, especially in textile, in
the bioprocessing of natural fibers, such as for the hydrolysis of cellulose
to fermentable sugars and ethanol production (Tolan and Foody,
1999); de-inking of recycled paper (Smook, 1992; Moekerbak
and Zimmermann, 1998); biopolishing of cotton fabrics to enhance softness
and appearance and treatment of recycled fibers to restore fiber texture and
flexibility lost during operations (Smook, 1992; Moekerbak
and Zimmermann, 1998; Bhat et al., 1991;
Pommier et al.,1989), in pulp and paper industries
(Godfrey and West, 1996; Harman and
Kubicek, 1998; Saddler, 1993; Uhlig,
1998). It has also been shown that cellulase treatment in combination with
physical refining can provide a means for altering the morphology of coarse
wood fibers (e.g., Douglas fir) to produce finer paper products (Mansfield
et al., 1999). A number of review works are available on the production
and application of microbial cellulases (Sukumaran et
al., 2005), but the increasing application of cellulases in various
sectors of food, textile and allied industries demand the understanding of the
exact mechanism of action of these enzymes Therefore, the present review intends
to highlight the recent researches on the mode of action of microbial cellulases
of commercial significance and their main uses in various industries.
Mode of action: Before studying the applications of the cellulase enzyme,
one needs to know the mode of action of the enzyme and the actual role of each
component of the enzyme in performing the specific reaction. A cellulose enzyme
system consists of three major components: endoglucanase (EC 22.214.171.124), exoglucanase
(EC 126.96.36.199) and β-glucosidase (EC 188.8.131.52). of which endoglucanase-
(EC 184.108.40.206; 1,4-β-D-glucan glucanohydrolase) acts on carboxy methyl cellulose,
causing random scission of cellulose chains yielding glucose and cello-oligosaccharides;
exoglucanase-(EC 220.127.116.11; 1,4-β-D-glucan cellobiohydrolase) acts on microcrystalline
cellulose (avicel),imparting an exo-attack on the non-reducing end of cellulose,
liberating cellobiose as the primary product and beta-glucosidases (EC 18.104.22.168)
that facilitates the hydrolysis of cellobiose to glucose (Fig.
1). All these enzymes act synergistically to release glucose as end product.
The commonly described mode of action for cellulases on polymers is either exo-or
endo-cleavage and all cellulases target the specific cleavage of β-1,4-glycosidic
bonds (Wood and McCrae, 1979).
|| Mode of action of various components of cellulase
Endo-β-glucanase acts randomly on the cellulose chain, to produce cello-oligosaccharides,
while exo-β-glucanase acts on exposed chain ends by splitting off cellobiose.
Cellobiose is subsequently hydrolysed by cellobiase to form glucose. This hypothesis
is however more applicable and acceptable worldwide for the decomposition of
Cellulases are composed of independently folding, structurally and functionally
discrete units called domains or modules, making cellulases module (Henrissat
et al., 1998). A free cellulase is composed of a Carbohydrate Binding
Domain (CBD) at the C-terminal joined by a short poly-linker region to the catalytic
domain at the N-terminal. There are only two modes of action for the hydrolysis
of cellulose by cellulases, either inversion or retention of the configuration
of the anomeric carbon. At least two amino acids with carboxyl groups located
within the active site catalyze the reaction by acid-base catalysis. Using this
classification system, cellobiohydrolases (exoglucanases) were classified as
exo-acting based on the assumption that they all cleave β-1,4-glycosidic
bonds from chain ends. As well, those enzymes truly exo-acting often have a
tunnel-shaped closed active site which retains a single glucan chain and prevents
it from re-adhering to the cellulose crystal (Rouvinen et
al., 1990; Divne et al., 1994, 1998).
While endoglucanases on the other hand, are often classified as endo-acting
cellulases because they are thought to cleave β-1,4-glycosidic bonds internally
only and appear to have cleft-shaped open active sites. Endoglucanase are active
on amorphous regions of cellulose and thus their activity can be assayed using
soluble cellulose substrates; i.e., the carboxymethylcellulase assay (CMCase).
However, there is evidence that some cellulases display both action, endo-and
exo-function (Davies and Henrissat, 1995). Thus classification
has changed; cellobiohydrolases (exoglucanases) are described as active on the
crystalline regions of cellulose; whereas, endoglucanases are typically active
on the more soluble amorphous region of the cellulose crystal. There is a high
degree of synergy seen between cellobiohydrolases (exoglucanases) and endoglucanases
and it is this synergy that is required for the efficient hydrolysis of cellulose.
The products of endoglucanases and cellobiohydrolases, that are cellodextrans
and cellobiose, respectively, are inhibitory to the enzymes activity.
Thus, efficient cellulose hydrolysis requires the presence of β-glucosidases
which cleaves the final glycosidic bonds producing glucose (end product). Typically
cellobiose and cellodextrins are taken up by the microorganism and internally
cleaved via cellodextrin phosphorylases or cellobiose phosphorylases to create
glucose monophosphate, which is energetically favoured. Some bacteria also produce
inter-or extra-cellular β-glucosidases to cleave cellobiose and cellodextrins
and produce glucose to be taken up by or assimilated by the cell. Mechanism
of cellulose degradation by aerobic bacteria is similar to that of aerobic fungi
but it is clear that anaerobic bacteria operate a different system (Coughlan
et al., 1988). The cellulolytic systems of anaerobic bacteria have
received in-depth study of late. Cellulase complexes located on the cell surface
mediate adherence of anaerobic cellulolytic bacteria to the substrate. Evidence
indicates that the anaerobic cellulolytic bacteria must attach themselves to
cellulose to effect its degradation. Lamed and Bayer (1988)
coined the term cellulosome to describe the multicomponent cellulolytic complex
produced by C. thermocellum. Aggregates of these cellulosomes, i.e.,
polycellulosomes, located on the cell surface are responsible for attachment
of the cell to the substrate, this adherence being specific for cellulose. The
cellulosome, concept was originally proposed in case of the cellulase system
of the thermophilic anaerobe Clostridium thermocellum. In this bacterium,
the cellulosome is composed of a primary scaffoldin subunit that can bind up
to nine enzymes into the complex, a process mediated by very strong intermodular
interactions (Fig. 2). Free cellulase system which generally
contain individual enzymes that bear a catalytic module together with a Cellulose-Binding
|| Schematic representation of the structure of cellulosome
present in a bacterial cell membrane
But in case of cellulosomal systems the scaffoldin subunit contains a single
CBM together with numerous cohesion modules. The cohesion modules, in turn,
bind strongly to a dockerin module borne by each cellulosomal enzyme. Cellulosomes
derived from different bacteria show a divergent type of architecture, owing
to the number of interacting scaffoldins and the content and specificities of
their resident cohesins (Bayer et al., 2004).
Cellulosomes of some bacteria like Acetivibrio cellulolyticus and Ruminococcus
flavefaciens, can be much more intricate than those of C. thermocellum
(Xu et al., 2004; Jindou,
et al., 2006); the heterogeneity of cellulosome composition and assembly
is still a mystery and an area of current research. A poly-cellulosome isolated
from residual cellulose in cultures of C. thermocellum strain JW20 was
found to have a diameter of 60 mm and a calculated mass of from 50 to 80x10
6 Da. It is comprised of a number of tightly packed spherical entities, viz.,
cellulosome, (16 to 18 nm in diameter) with a mass of 2 to 2.5x10 6 Da. The
cellulosomes in turn are comprised of about 35 polypeptides ranging from 45
kDa to about 200 kDa. A polypoptide of 200-210 kb, which in the case of C.
thermocellum responsible for attachment of the complex to the cell and to
the substrate, is present in the complex produced by each organism. Presence
of enzymes on the cell surface may make possible the topological arrangement
required for hydrolysis of crystalline substrates. Anaerobic cellulolytic bacteria
contain a β-glucosidase or cell bound cellobiose phosphorylase or both.
ROLE OF MICROBIAL CELLULASE IN VARIOUS INDUSTRIES
Cellulases have a wide range of enormous potential applications in biotechnology
and many thermo stable endoglucanase appeared to have a great potentiality for
industrial use (Karmakar and Ray, 2010a). In most of
the cases they are used with hemicelluloses, pectinases, ligninase and allied
enzymes. Some of the most important applications of cellulases are in food,
brewery and wine, animal feed, textile and laundry, pulp and paper industries,
as well as in agriculture and for research purposes. Details of most promising
applications are discussed below.
Cellulase in food processing industries: Enzyme infusion has the potential
of producing fruit and vegetable juices which is very important from commercial
standpoint. The production of fruit and vegetable juices requires methods for
extraction, clarification and stabilization. During early 1930s, when fruit
industries began to produce juice, the yields were low and many difficulties
were encountered in filtering the juice to an acceptable clarity (Uhlig,
1998). Subsequently, research on industrially suitable macerating enzymes
from food-grade micro-organisms (Aspergillus niger and Trichoderma
sp.), together with increased knowledge on fruit components, helped to overcome
these difficulties (Grassin and Fauquembergue, 1996).
During the production of juice from fruits such as apples and pears, the whole
fruits were crushed to pulp mash, which, after mechanical processing (pressing,
centrifuging and filtering), resulted into a clear fruit juice and a solid phase
called pomace (Galante et al., 1998). Application
of macerating enzymes could increase both production and process performance
without additional capital investment. Macerating enzymes are generally used
after crushing, to macerate the fruit pulp for partial or complete liquifaction,
which increases the juice yield, reduces the processing time and improves the
extraction of valuable fruit components. Thus, the macerating enzymes, composed
of mainly cellulase and pectinase play a key role in food biotechnology and
their demand will likely increase for extraction of juice from a wide range
of fruits and vegetables including olive oil extraction, that has attracted
the world market because of its numerous health claims. In addition, the infusion
of pectinases and b-glucosidases increases the aroma and volatile characteristics
of specific fruits and vegetables (Humpf and Schrier, 1991;
Krammer et al., 1991; Marlatt
et al., 1992; Pabst et al., 1991).
Cellulase in pharmaceutical industries: Since, humans poorly digest cellulose fiber, taking a digestive enzyme product, like Digestin, that contains cellulase enzymes is not only necessary, but also vital for healthy cells.
Cellulase in brewery and wine industries: Bioconversion of cellulosic
materials to bioalcohol involves a multistep process which first uses cellulolytic
enzymes for hydrolysis of polymers to pentose/hexose sugars and fermentation
followed by distillation of these sugars into ethanol. In the beer wort production,
Pajunen (1986) opined that the enzyme preparation from
Trichoderma was the best as judged by its cost /performance ratio. In
an earlier study, Oksanen et al. (1985) observed
that endoglucanase II and cellobiohydrolase II of the Trichoderma cellulase
system were responsible for a maximum reduction in the degree of polymerisation
and wort viscosity. Furthermore, a marked improvement in filterability was reported
with increasing doses of enzyme when tested in pilot scale (Oksanen
et al., 1985). Significant and reproducible improvements in grape
pressability, settling rate and total juice yield were achieved using a combination
of macerating enzymes. Such improvements were noticeable only with a correct
balance of pectinolytic, cellulolytic and hemicellulolytic enzymes. Using three
varieties (Soave, Chardonnay and Sauvignon) of white grapes from Northern Italy,
Galante et al. (1998) assessed the performance
of Cytolase 219 (a commercial enzyme preparation, derived from Trichoderma
and Aspergillus, containing pectinase, cellulase and hemicellulase)
in wine making. They reported a 10-35% increase in the extraction of the first
wine must, a 70-180% increase in the must filtration rate, significant improvement
in wine stability, 50120 min decrease in pressing time, 30-70% decrease
in must viscosity and 20-40% energy saving during cooling of fermenters. In
fact, the enzyme technology offers enormous benefits to wine industry.
Cellulase in textile industries: Enzymes have been used in the leather
industry for many years and more recently have been introduced into modern textile
industries. Depending on the aim, the extent of cellulose degradation and the
properties of the resulting products can be controlled by adjusting the treatment
parameters (like time, enzyme concentration and the composition of cellulase
mixture). The textile industries take advantage of both complete and individual
cellulase components to achieve partial cellulose hydrolysis and improve fabric
properties, where the cellulase would act upon the fibre to reduce the cell
wall thickness and would make the fibre more flexible and collapsible. While
in case of bio-polishing, endoglucanase rich cellulase would act for depiling
and aging of the fabric. For example, complete cellulase mixtures are used in
depilling/cleaning of cotton fabrics, whereas, pure endoglucanase (EG) or EG-rich
mixtures are used to produce aged and soft fabrics demanded by the fashion market
(Tolan and Foody, 1999; Cavaco-Paulo,
1998). It is postulated that during depilling, enzymes attack and hydrolyze
the microfibrils that hold the pills to the fiber surface, whereas in fabric
ageing, the attack occurs on the fiber surface and results in fiber defibrillation
(Cavaco-Paulo, 1998). The accompanying mechanical action
removes the dye bound to the surface and imparts an aged appearance (Cavaco-Paulo,
1998). In both cases, the accessibility of cellulose surface to the enzymes
plays a key role. Blue jeans and other denim garments have gained remarkable
popularity in recent years. In denim fabrics, the indigo dye is mostly attached
to the surface of the yarn and to the most exterior short cotton fibres. Repeated
washings of denim fabric showed the wash down or aged effect, on which the entire
denim industry has been built. Commercial cellulases have also been shown to
enhance the whiteness, brightness and color characteristics of cotton fabrics
(Csiszar et al., 1998). The cellulase preparations
capable of modifying the structure of cellulose fibrils are added to laundry
detergents to improve the colour brightness, hand feel and dirt removal from
cotton and cotton blend garments. Most cotton or cotton blend garments, during
repeated washings, tend to become fluffy and dull. This is mainly due to the
presence of partially detached microfibrils on the surface of garments that
can be removed by cellulases in order to restore a smooth surface and original
colour to the garment. Also, the degradation of microfibrils by cellulase, softens
the garment and removes dirt particles trapped in the microfibril network. The
retention of water by fibers during refining reduces the softening temperature
of hemicellulose and lignin present between adjacent fibers and weakens inter-fiber
bonding, hence improving the separation of fibers from one another and reducing
the energy consumption during refining operation (Pere et
al., 1996). It has been shown that cellobiohydrolase I, a cellulase
component from Trichoderma reesei, could selectively reduce the crystallinity
of cellulose and subsequently produce more amorphous material with a higher
affinity for water. Treatment with CBH I was able to reduce the refining energy
demands by 40% (Pere et al., 1996). The finishing
of denim jeans has also become a popular application for cellulases in the textile
industry. Traditionally denim was stonewashed with pumice stones to fade the
surface of the garment. A small application of cellulase can replace many of
the stones resulting in less damage to the garments and machinery. This technique
has become known as Biostoning and can result in much greater fading without
high abrasive damage both to the actual fabric and any other accessories (buttons,
rivets) on the fabric. Stonewashing enzymes are usually available as either
acid cellulases (optimum activity around 4.5) or neutral cellulases (optimum
activity at just below pH 7.0).
Cellulase in detergent industries: Use of cellulase along with protease
and lipase is a more recent innovation (Singh et al.,
2007). Removal of oil from interfibre space by selective contraction of
fibres by the alkaline cellulase increases the cleansing capacity of a detergent.
Nowadays, liquid laundry detergent containing anionic or nonionic surfactant,
citric acid or a water-soluble salt, proteolytic enzyme, cellulase and a mixture
of 1,2 propane diol and boric acid or its derivative. The compositions are prepared
by adding the diol and boric acid before adding the citric acid/salt to the
composition. This order of addition improves the stability of the cellulase
(Boyer and Farwick, 1995) As most of the cellulose fibres
in the modern textile industry enzymes are used increasingly in the finishing
of fabrics and clothes are arranged as long, straight chains some small fibres
can protrude from the yarn or fabric. The correct application of a cellulase
enzyme can remove these rough protuberances giving a smoother, glossier brighter
colored fabric. This technique has become known biopolishing and results in
not only a softer fabric but also improved color brightness. This process of
washing has been adapted and included in some laundry detergents.
Applications of cellulase in pulp and paper industries: Use of cellulases
along with xylanase and ligninase in the pulp and paper industries has increased
considerably during last decade (Mai et al., 2004).
Biopulping with the help of cellulases and allied enzymes is a better alternative
for mechanical pulping process as the former provides significant energy savings
as these enzymes require lower energy input to achieve the required freeness
and strength and check the problem of pollution. Refining, of primary or secondary
fibers, can generate small particles (fines) that can reduce the drainage rate
of pulps during papermaking operations. Cellulases seem to preferentially attack
and hydrolyze the fines produced during the refining operation and therefore,
improve the pulp's drainage property. Cellulase and hemicellulases helps in
modification of coarse mechanical pulp and handsheet strength properties, partial
hydrolysis of carbohydrate molecules and the release of ink from fibre surfaces
which results into deinking of recycled paper. Cellulases have also been used
to remove ink from papers and to enhance papermaking properties of recycled
fibers. Enzymatic deinking can lower the need for deinking chemicals and reduce
the adverse environmental impacts of the paper industry (Stork
and Puls, 1996). While in general, enzymatic deinking results in little
or no loss in fiber strength (Stork and Puls, 1996; Sarkar
et al., 1995; Sarkar, 1997), the overall
effectiveness of the treatment depends on variables, such as toner quality and
type, the type and amount of sizing and the presence of other contaminants (Sarkar
et al., 1995). Although, strength properties have not been compromised
substantially, the excessive use of enzymes must be avoided (Stork
and Puls, 1996), as it has been shown that significant hydrolysis of the
fines (Stork and Puls, 1996; Jeffries
et al., 1996; Ow et al., 1996; Jackson
et al., 1993) could reduce the bondability of the fibers (Karnis,
1995; Kibblewhite, 1975). It has been postulated
that improvements in dewatering and deinking of various pulps results in the
peeling of the individual fibrils and bundles, which have a high affinity for
the surrounding water and ink particles (Kibblewhite et
al., 1995). It appears that cellulase treatments can release ink particles
bound to the fines and to the fiber and enhance the removal of ink by floatation.
While cellulases clearly enhance the deinking process, the mechanical agitation
still plays a critical role in the efficiency of ink removal. These claims are
consistent with similar findings concerning enzymatic stone washing of cotton
fabrics, which indicated that enzymatic treatments in combination with mechanical
agitation improve the efficacy of the process (Lee and Kim,
1983; Welt and Dinus, 1995; Zeyer
et al., 1993).
Application of cellulase in animal feed: Cellulases have potential application
in animal feed industry consumed by poultry, pigs, ruminants as well as pet
and fish farming. In todays world there is a great deal of interest in using
enzyme preparations containing high levels of cellulase and hemicellulase activities
for improving the feed utilization, milk yield and body weight gain by ruminants.
Nevertheless, the successful use of these enzymes in animal diet is to: eliminate
Anti-Nutritional Factors (ANF) present in grains or vegetables; degrade certain
cereal components in order to improve the nutritional value of feed; and/or
to supplement animals own digestive enzymes (e.g., proteases, amylases
and glucanases). Moreover, Cellulases and hemicellulases are responsible for
partial hydrolysis of lignocellulosic materials, dehulling of cereal grains,
hydrolysis of b-glucans and better emulsification and flexibility of feed materials
which results in the improvement in the nutritional quality of animal feed (Chesson,
1987; Cowan, 1996; Galante et
al., 1998). Cellulases, hemicellulases and pectinases can cause partial
hydrolysis of plant cell wall during silage and fodder preservation. They are
responsible for the expression of preferred genes in ruminant and monogastric
animals for high feed conversion efficiency. These commercially important enzymes
can produce and preserve high quality fodder for ruminants; improving the quality
of grass silage (Ali et al., 1995; Hall
et al., 1993; Selmer-Olsen et al., 1993).
Application of cellulases in research and development: Mixture of different
cellulase along with hemi-cellulase and pectinase have immense potential and
application in research and development area for controlling plant diseases
and enhancing plant growth. A cocktail of different cellullases,hemicellulases
and pectinases results in the solubilisation of fungal or plant cell wall to
produce protoplast (Beguin and Aubert, 1994; Bhat
and Bhat, 1997). Cellulases and related enzymes are used in the biocontrol
of plant pathogens and different plant diseases by inhibiting the germination
of spores of the plant pathogens (Benitez et al.,
1998; Chet et al., 1998). Even the cellobiohydrolase
promoters of Tricoderma is used for the expression of the different proteins,
enzymes, antibodies in large amount. These are some of the main cellulase application
in the research area (Dunn-Coleman et al., 1991;
Harkki et al., 1989; Penttila,
Application in waste utilization: Cellulose is the major part of plant
biomass. Therefore, the wastes generated from forests, agricultural fields and
agro industries contain a large amount of unutilized or underutilized cellulose.
Agricultural and industrial wastes are among the causes of environmental pollution
(Milala et al., 2005.) These wastes generally
accumulate in the environment causing pollution problem (Abu
et al., 2000). Nowadays, these so called wastes are judiciously
converted into valuable products such as enzymes (Ray
et al., 1994) Sugar (Ghosh and Ray, 2010), biofuels,
chemicals, cheap energy sources for fermentation, improved animal feeds and
human nutrients (Howard et al., 2003), which
is accomplished by cellulase. Therefore, the discarded biomass and agrowastes
are successfully utilized for the production of enzymes, sugar and alcohols
(Karmakar and Ray, 2010b; Youssef
and Berekaa, 2009; Acharya et al., 2008;
Milala et al., 2009; Omosajola
et al., 2008).
It was estimated that in 2000, the world sale of industrial enzymes have already
reached a market of 1.6 billion US dollars (Demain, 2000)
of which cellulase and allied enzymes occupy a significant position. Microbes
are an attractive topic of interest for the production of cellulases and hemicellulases
due to their immense potential for cellulase production, enzyme complexity and
extreme habitat variability. Microbial cellulases are preferred for their vast
industrial applicability and relatively lower cost of production. In fact the
craze for these cellulase enzymes is increasing day by day worldwide for their
use in food, pharmaceuticals, bioalcohols and other industries. More and more
research works are resulting into improved scientific knowledge along with the
success of meeting the growing demands of the cellulase and related enzymes
for generation of environment friendly textiles, detergents, bio-pulping and
bio-alcohols. Moreover, it is opening new avenues for utilization of various
agrowastes and organic pollutants as a source of renewable resource instead
of dumping them to cause environmental pollution. In near future newer knowledge
of excellent cellulolytic and hemicellulolytic systems and adoption of different
biotechnological strategies will definitely bring a great prospect in industrial
The authors wish to thank the Department of Science and Technology (DST), West Bengal, India for the financial assistance.
1: Abu, E.A., P.C. Onyenekwe, D.A. Ameh, A.S. Agbaji and S.A. Ado, 2000. Cellulase (E.C.3.21.3) production from sorghum bran by Aspergillus niger SL 1: An assessment of pretreatment methods. Proceedings of the International Conference on Biotechnology: Commercialization and Food Security, (ICBCFS`00), Abuja, Nigeria, pp: 153-159
2: Acharya, P.B., D.K. Acharya and H.A. Modi, 2008. Optimization for cellulase production by Aspergillus niger using saw dust as substrate. Afr. J. Biotechnol., 7: 4147-4152.
Direct Link |
3: Ali, S., J. Hall, K.L. Soole, C.M.C.A. Fontes, G.P. Hazlewood, B.H. Hirst and H.J. Gilbert, 1995. Targeted Expression of Microbial Cellulases in Transgenic Animals. In: Carbohydrate Bioengineering Progress in Biotechnology, Petersen, S.B., B. Svensson and S. Pedersen (Eds.). Vol. 10. 1st Edn., Elsevier, Amsterdam, ISBN-10: 0444822232, pp: 279-93
4: Bajpai, P., 1999. Applications of enzymes in the pulp and paper industry. Biotechnol. Prog., 15: 147-157.
5: Bayer, E.A., E. Morag and R. Lamed, 1994. The Cellulosome: A treasure-trove for biotechnology. Trends Biotechnol., 12: 379-386.
6: Bayer, E.A., J.P. Belaich, Y. Shoham and R. Lamed, 2004. The cellulosomes: Multi-enzyme machines for degradation of plant cell wall polysaccharides. Ann. Rev. Microbiol., 58: 521-554.
CrossRef | Direct Link |
7: Bhat, M.K. and S. Bhat, 1997. Cellulose degrading enzymes and their potential industrial applications. Biotechnol. Adv., 15: 583-620.
CrossRef | Direct Link |
8: Bhat, M.K., 2000. Cellulases and related enzymes in biotechnology. Biotechnol. Adv., 18: 355-383.
Direct Link |
9: Bhat, G., J. Heitmann and T. Joyce, 1991. Novel techniques for enhancing the strength of secondary fiber. Tappi, 74: 151-156.
Direct Link |
10: Beguin, P. and J.P. Aubert, 1994. The biological degradation of cellulose. FEMS Microbiol. Rev., 13: 25-58.
11: Benitez, T., C. Limon, J. Delgado-Jarana and M. Rey, 1998. Glucanolytic and Other Enzymes and their Genes. In: Trichoderma and Gliocladium-Enzymes, Biological Control and Commercial Applications, Harman, G.F. and C.P. Kubicek (Eds.). Vol. 2. Taylor and Francis, London, ISBN: 978-0-7484-0805-4, pp: 101-127
12: Boyer, S.L. and T.J. Farwick, 1995. Liquid laundry detergents with citric acid, cellulase and boricdiol complex to inhibit proteolytic enzyme. United States Patent 5476608. http://www.freepatentsonline.com/5476608.html.
13: Cavaco-Paulo, A., 1998. Processing Textile Fibers with Enzymes: An Overview. In: Enzyme Applications in Fiber Processing, Eriksson, K.E. and A. Cavaco-Paulo (Eds.). American Chemical Society Washington, DC., ISBN-13: 9780841235472, pp: 180-189
14: Chesson, A., 1987. Supplementary Enzymes to Improve the Utilization of Pigs and Poultry Diets. In: Recent Advances in Animal Nutrition, Haresign, W. and D.J.A. Cole (Eds.). Butterworths, London, ISBN: 10-0407011633, pp: 71-89
15: Chet, I., N. Benhamou and S. Haran, 1998. Mycoparasitism and Lytic Enzymes. In: Trichoderma and Gliocladium-Enzymes, Biological Control and Commercial Applications, Harman, G.F. and C.P. Kubicek (Eds.). Vol. 2. Taylor and Francis, London, pp: 327-342
16: Cowan, W.D., 1996. Animal Feed. In: Industrial Enzymology, Godfrey, T. and S. West (Eds.). 2nd Edn., Macmillan Press, Nature Publishing Group, London, pp: 360-371
17: Csiszar, E., G. Szakacs and I. Rusznak, 1998. Bioscouring of Cotton Fabrics with Cellulase Enzyme. In: Enzyme Applications in Fiber Processing, Eriksson, K.E. and A. Cavaco-Paulo (Eds.). American Chemical Society, Washington, DC., ISBN-13: 9780841235472, pp: 204-211
18: Davies, G.J. and B. Henrissat, 1995. Structures and mechanisms of glycosyl hydrolases. Structure, 3: 853-859.
19: Demain, A.L., 2000. Microbial biotechnology. Trends Biotechnol., 18: 26-31.
CrossRef | PubMed | Direct Link |
20: Divne, C., J. Stahlberg, T. Reinikainen, L. Ruohonen and G. Petterson et al., 1994. The three-dimensional crystal structure of the catalytic core of cellobiohydrolase I from Trichoderma reesei. Science, 265: 524-528.
21: Divne, C., J. Stahlberg, T. Teeri and T.A. Jones, 1998. High-resolution crystal structures reveal how a cellulose chain is bound in the 50 A long tunnel of cellobiohydrolase I from Trichoderma reesei. J. Mol. Biol., 275: 309-325.
22: Dunn-Coleman, N.S., P. Bloebaum, R.M. Berka, E. Bodie and N. Robinson et al., 1991. Commercial levels of chymosin by Aspergillus. Biotechnology, 9: 976-981.
CrossRef | Direct Link |
23: Galante, Y.M., A. De Conti and R. Monteverdi, 1998. Application of Trichoderma Enzymes in Food and Feed Industries. In: Trichoderma and Gliocladium-Enzymes, Biological Control and Commercial Applications, Harman, G.F. and C.P. Kubicek (Eds.). Vol. 2. CRC Press, London, UK., ISBN: 978-0-748-40805-4, pp: 327-42
24: Ghosh, B. and R.R. Ray, 2010. Saccharification of raw native starches by extracellular isoamylase of Rhizopus oryzae. Biotechnology, 9: 224-228.
CrossRef | Direct Link |
25: Gilbert, H.J. and G.P. Hazlewood, 1993. Bacterial cellulases and xylanases. J. Gen. Microbiol., 139: 187-194.
Direct Link |
26: Godfrey, T. and S. West, 1996. Industrial Enzymology. 2nd Edn., Macmillan Publishers Inc., New York
27: Grassin, C. and P. Fauquembergue, 1996. Fruit Juices. In: Industrial Enzymology, Godfrey, T. and S. West (Eds.). 2nd Edn., Macmillan, UK., pp: 226-234
28: Hall, J., A. Simi, M.A. Surani, G.P. Hazlewood and A.J. Clark et al., 1993. Manipulation of the repertoire of digestive enzymes secreted into the gastrointestional tract of transgenic mice. Biol. Technol., 11: 376-379.
29: Harkki, A., J. Uusitalo, M. Bailey, M. Penttila and J.K.C. Knowles, 1989. A novel fungal expression system: Secretion of active calf chymosin from the filamentous fungus Trichoderma reesei. Nature Biotechnol., 7: 596-603.
30: Harman, G.E. and C.P. Kubicek, 1998. Trichoderma and Gliocladium: Enzymes, Biological Control and Commercial Applications. Vol. 2. Taylor and Francis Ltd., CRC Press, London, USA., pp: 393
31: Henrissat, B., T.T. Teeri, R.A.J. and A.Warren, 1998. Scheme for designating enzymes that hydrolyse the polysaccharides in the cell walls of plants. FEBS Lett., 425: 352-354.
32: Howard, R.L., E. Abotsi, R.E.L. Jansen and S. Howard, 2003. Lignocellulose biotechnology: Issue of bioconversion and enzyme production. Afr. J. Biotechnol., 2: 602-619.
Direct Link |
33: Humpf, H.U. and P. Schrier, 1991. Bound aroma compounds from the fruit and the leaves of Blackberry (Rubus laciniata L.). J. Agric. Food Chem., 39: 1830-1832.
CrossRef | Direct Link |
34: Jackson, L.S., J.A. Heitmann and T.W. Joyce, 1993. Enzymatic modifications of secondary fiber. Tappi, 76: 147-154.
Direct Link |
35: Jeffries ,T.W., M.S. Sykes, K. Rutledge-Cropsey, J.H. Klungness and S. Abubakr, 1996. Enhanced Removal of Toners form Office Waste Papers by Microbial Cellulases. In: Biotechnology in the Pulp and Paper Industry: Recent Advances in Applied and Fundamental Research, Srebotnik, E. and K. Messner (Eds.). Vol. 1. Vienna, Austria, pp: 141-144
36: Jindou, S., I. Borovok, M.T. Rincon, H.J. Flint and D.A. Antonopoulos et al., 2006. Conservation anddivergence in cellulosome architecture between two strains of Ruminococcus flavefaciens. J. Bacteriol., 188: 7971-7976.
37: Karmakar, M. and R.R. Ray, 2010. Characterization of extracellular thermostable endoglucanase from Rhizopus oryzae using response surface methodology. Res. Rev. Biosci., 4: 50-55.
Direct Link |
38: Karmakar, M. and R.R. Ray, 2010. Extra cellular endoglucanase production by rhizopus oryzae in solid and liquid state fermentation of agro wastes. Asian J. Biotechnol., 2: 27-36.
39: Karnis, A., 1995. The role of latent and delatent mechanical pulp fines in sheet structure and pulp properties. Paperi ja Puu-Paper Timber, 77: 491-497.
Direct Link |
40: Kibblewhite, R.P., 1975. Interrelations between pulp refining treatments, fiber and fines quality and pulp freeness. Paperi ja Puu-Paper Timber, 57: 519-526.
41: Kibblewhite, R.P., A.D. Bawden and C.L. Brindley, 1995. TMP fiber and fines qualities of 13 radiata pine wood types. APPITA, 48: 367-377.
Direct Link |
42: Krammer, G., P. Winterhalter, M. Schwab and P. Schrier, 1991. Glycosidically bound aroma compounds in the fruits of prunus species: Apricot (P. armeniaca, L.), Peach (P. persica, L.), Yellow plum (P. domestica, L. ssp. Syriaca). J. Agric. Food Chem., 39: 778-781.
CrossRef | Direct Link |
43: Ladisch, M.R., K.W. Lin, M. Voloch and G.T. Tsao, 1983. Process considerations in the enzymatic hydrolysis of biomass. Enz. Microb. Technol., 5: 82-100.
44: Lamed, R. and E.A. Bayer, 1988. The cellulosome of Clostridium thermocellum. Adv. Applied Microbiol., 33: 1-46.
45: Lee, S.B. and I.H. Kim, 1983. Structural properties of cellulose and cellulase reaction mechanisms. Biotechnol. Bioeng., 25: 33-51.
46: Mai, C., U. Kues and H. Miltz, 2004. Biotechnology in the wood industry. Applied Microbiol. Biotechnol., 63: 477-494.
CrossRef | Direct Link |
47: Mansfield, S.D., D.J. Swanson, N. Roberts, J.A. Olson and J.N. Saddler, 1999. Enhancing douglas-fir pulp properties with a combination of enzyme treatments and fiber fractionation. Tappi, 82: 152-158.
48: Marlatt, C., C.T. Ho and M. Chien, 1992. Studies of aroma constituents bound as glycosides in tomato. J. Agric. Food Chem., 40: 249-252.
CrossRef | Direct Link |
49: Coughlan, M.P. and L.G. Ljungdahl, 1988. Comparative Biochemistry of Fungal and Bacterial Cellulolytic Enzyme Systems. In: Biochemistry and Genetics of Cellulose Degradation, Aubert, J.M., P. Beguin and J. Millet (Eds.). Academic Press, London, pp: 11-30
50: Milala, M.A., A. Shugaba, A. Gidado, A.C. Ene and J.A. Wafar, 2005. Studies on the use of agricultural wastes for cellulase enzyme production by Aspergillus niger. Res. J. Agric. Biol. Sci., 1: 325-328.
51: Milala, M.A., B.B. Shehu, H. Zanna and V.O. Omosioda, 2009. Degradation of agro-waste by cellulase from Aspergillus candidus. Asian J. Biotechnol., 1: 51-56.
CrossRef | Direct Link |
52: Moekerbak, A.L. and W. Zimmermann, 1998. Applications of Enzymes in Paper Deinking Processes. In: Enzyme Applications in Fiber Processing, Eriksson, K. and A. Cavaco-Paulo (Eds.). Vol. 687. American Chemical Society, Washington, D.C., ISBN-13: 9780841235472e, pp: 133-141
53: Narasimha, G., A. Sridevi, B. Viswanath, M.S. Chandra and R.B. Rajasekhar, 2006. Nutrient effects on production of cellulolytic enzymes by Aspergillus niger. Afr. J. Biotechnol., 5: 472-476.
Direct Link |
54: Oksanen, J., J. Ahvenainen and S. Home, 1985. Microbial cellulase for improving filtrability of wort and beer. Proceedings of the European Brew Chemistry Conversation Helsinki, (EBCCH`85), IRL Press Ltd., Oxford, pp: 419-425
55: Omosajola, P.F. and O.P. Jilani, 2008. Cellulase production by Trichoderma longi, Aspergillus niger, Saccharomyces cerevisae cultured on Waste Materials from orange. Pak. J. Biol. Sci., 11: 2382-2388.
Direct Link |
56: Ow, S.K., J.M. Park and S.H. Han, 1996. Effects of Enzyme on Ink Size and Distribution In: Biotechnology in the Pulp and Paper Industry: Recent Advances in Applied and Fundamental Research, Srebotnik, E. and K. Messner (Eds.). Facultas-Universitatsverlag, Vienna, Austria, pp:163-168
57: Pabst, A., D. Barron, P. Etievant and P. Schrier, 1991. Enzymatic hydrolysis of bound aroma constituents from raspberry fruit pulp. J. Agric. Food Chem., 39: 173-175.
58: Pajunen, E., 1986. Optimal use of B-Glucanases in Wort Production. In: EBC-Symposium on Wort Production, Kurtzman, C.P. and J. Fell (Eds.). Monograph, X.I. Maffliers, France, pp: 137-148
59: Penttila, M., 1998. Heterologous Protein Production in Trichoderma. In: Trichoderma and Gliocladium-Enzymes, Biological Control and Commercial Applications, Harman, G.F. and C.P. Kubicek (Eds.). Vol. 2. Taylor and Francis, London, pp: 365-382
60: Pere, J., M. Siika-Aho, L. Viikari, S. Liukkonen, J. Gullichsen, 1996. Use of purified enzymes in mechanical pulping. TAPPI Pulping Con., 2: 693-696.
Direct Link |
61: Pommier, J., J. Fuentes and G. Goma, 1989. Using enzymes to improve the process and the product quality in the recycled paper industry, part 1: The basic laboratory work. Tappi, 72: 187-191.
62: Poutanen, K., 1997. Enzymes: An important tool in the improvement of the quality of cereal foods. Trends Food Sci. Technol., 8: 300-306.
63: Ray, R.R., S.C. Jana and G. Nanda, 1994. Saccharification of indigenous starches by β-amylase of Bacillus megaterium. World J. Microbiol. Biotechnol., 10: 691-693.
64: Rouvinen, J., T. Bergfors, T.T. Teeri, J.K.C. Knowles and T.A. Jones, 1990. Three-dimensional structure of cellobiohydrolase II from Trichoderma reesei. Science, 249: 380-386.
65: Ryu, D.D.Y. and M. Mandels, 1980. Cellulases: Biosynthesis and applications. Enzyme. Microb. Technol., 2: 91-102.
CrossRef | Direct Link |
66: Saddler, J.N., 1993. Bioconversion of Forest and Agricultural Plant Residues (Biotechnology Agriculture Series). Vol. 9. CAB International, UK., Wallingford, Oxon, ISBN-13: 9780851987989, pp: 349
67: Sarkar, J., D. Cosper and E. Hartig, 1995. Applying enzymes and polymers to enhance the freeness of recycled fiber. TAPPI J., 78: 89-95.
Direct Link |
68: Sarkar, J.M., 1997. Recycle paper mill trial using enzyme and polymer for upgrading recycled fiber. APPITA, 50: 57-60.
69: Selmer-Olsen, I., A.R. Henderson, S. Robertson and R. McGinn, 1993. Cell wall degrading enzymes for silage. 1. The fermentation of enzyme-treated ryegrass in laboratory silos. Grass Forage Sci., 48: 45-54.
70: Singh, A., R.C. Kuhad and O.P. Ward, 2007. Industrial Applications of Microbial Cellulases. In: Lignocellulose Biotechnology: Future Prospects, Kuhad, R.C. and A. Singh (Eds.). I.K. International Publishing House Pvt. Ltd., New Delhi, ISBN: 81-88237-58-2, pp: 345-358
71: Smook, G., 1992. Secondary Fiber in Handbook for Pulp and Paper Technologists. Angus Wilde Publications, Vancouver, Canada, pp: 209-218
72: Stork, G. and J. Puls, 1996. Changes in Properties of Different Recycled Pulps by Endoglucanase Treatment. In: Biotechnology in the Pulp and Paper Industry: Recent Advances in Applied and Fundamental Research, Srebotnik, E. and K. Mesner (Eds.). Vol. 1. Facultas-Universitatsverlag, Vienna, pp: 145-150
73: Sukumaran, R.K., R.R. Singhania and A. Pandey, 2005. Microbial cellulases: Production, applications and challenges. J. Scient. Ind. Res., 64: 832-844.
Direct Link |
74: Tolan, J.S. and B. Foody, 1999. Cellulase from Submerged Fermentation. In: Advances in Biochemical Engineering/Biotechnology, Scheper, Th. (Ed.). Vol. 65. Springer, Berlin / Heidelberg, ISBN: 978-3-540-65577-0, pp: 41-67
75: Uhlig, H., 1998. Industrial Enzymes and Their Applications. John Wiley and Sons, USA., New York pp: 435
76: Voragen, A.G.J., 1992. Tailor-made enzymes in fruit juice processing. Fruit Process., 7: 98-102.
77: Welt, T. and R.J. Dinus, 1995. Enzymatic deinking: A review. Progress Paper Recycling, 4: 36-47.
Direct Link |
78: Wood, T.M. and S.I. McCrae, 1979. Synergism between enzymes involved in the solubilization of native cellulose. Adv. Chem. Ser., 181: 181-209.
79: Xu, Q., Y. Barak, R. Kenig, Y. Shoham, E.A. Bayer and R. Lamed, 2004. A novel Acetivibrio cellulolyticus anchoring scaffoldin that bears divergent cohesins. J. Bacteriol., 186: 5782-5789.
80: Youssef, G.A. and M.M. Berekaa, 2009. Improved production of endoglucanase enzyme by Aspergillus terreus: Application of plackett burman design for optimization of process parameters. Biotechnology, 8: 212-219.
CrossRef | Direct Link |
81: Zeyer, C., T.W. Joyce, J.W. Rucker and J.A. Heitmann, 1993. Enzymatic deinking of cellulose fabric: A model study for enzymatic paper deinking. Prog. Paper Recycling, 3: 36-44.