CELLULASES

Cellulases The EC number for this group of enzymes is EC 3.2.1.4.

Class of enzymes that catalyze cellulolysis (i.e. the hydrolysis of cellulose).

produced chiefly by fungi, bacteria, and protozoans

few other types of organisms, such as some termites and the microbial intestinal symbionts of other termites

Hydrolysis of 1,4-beta-D-glycosidic linkages in cellulose, producing primary products glucose,cellobiose and cello oligosaccharides

Types and Action Five types based on type of reaction catalysed

Endocellulases : breaks internal bonds to disrupt the crystalline structure of cellulose and expose individual cellulose polysaccharide chains

Exocellulases : cleaves 2 to 4 units from the ends of the exposed chains produced by endocellulase, resulting in the tetrasaccharides or disaccharides, such as cellobiose.

There are two main types of exocellulases [or cellobiohydrolases (CBH)] –

CBHI works processively from the reducing end CBHII works processively from the nonreducing end of

cellulose.

Cellobiase or beta-glucosidase: hydrolyses the exocellulase product into individual monosaccharides.

Oxidative cellulases: depolymerize cellulose by radical reactions, as for instance cellobiose dehydrogenase (acceptor).

Cellulose phosphorylases depolymerize cellulose using phosphates instead of water.

Mechanism of cellulysis

Microorganisms producing celluloseCelluloytic microbes are primarily carbohydrate

degraders

Cellulolytic microbes include bacteria Cellulomonas and Cytophaga , Cellovibrio

Fungi: tricoderma reesei , humicola, penicillium, Aspergillus yield high level of cellulases.

microbes commercially exploited for cellulase preparations are T.reesei, H. insolens, A. niger , Thermomonospora fusca, Bacillus sp. Etc.

Cellulase Production industrial demand for cellulases is being met by

production methods using submerged fermentation (SmF) processes

The cost of production in SmF systems is high and its uneconomical

Alternative methods like SSF systems make use of aerobic microorganisms

Production cost in the crude fermentation by SmF was about

$ 20/kg by SSF it was only $ 0.2/kg if in situ fermentation was used

Carbon sources for commercial cellulase fermentation: -cellulosic biomass -straw-spent hulls of cereals and pulses- Rice or wheat bran- paper industry waste - various lignocellulosic residues

Majority of processes are batch processes, attempts for fed batch and continuous process

Applications of CellulaseTextile Industry

Bio- Stonewashing of Denim garments- break down fabric (which is cellulose)- releases dye

Digesting off small fiber ends- better finishing

Providing localized variation in colourdensity.H. insolens cellulase is most commonly imployed

Laundry and DetergentsCellulase: EGIII and CBH I commonly used in detergentsCellulasepreparation from Humicola : active under mild alkaline condition and elevated temperatures are added in washing powder and in detergents.

Food and Animal Feed- Extraction and clarification of food and vegetables juices- Production of fruit nectars and purees- Extraction of olive oil- Glucanase: improves malting of barley in beer and wine production- Used in carotenoidextraction for production of food coloring agent- Cellulase with hemicellulase and pectinase is used to improve nutritive quality of forages- Increases digestibility of animal feed

Pulp and Paper industry- used for Biomechanical pulping- de-inking of recycled fibers- improving drainage and runnability of paper mills- used for characterization of pulp fibers- preparation of easily biodegradable cardboards.

Production of biofuel (Utilization of lignocellulosic waste)Steps:1) Pretreatment of lignocellulosic residue to remove lignin and hemicellulase fraction2) Cellulase treatment at 50̊ C to hydrolysecellulosic residues to generate fermentable sugars3) Use of fermentative micro-organism to produce alcohol from the hydrolysed cellulosic material

Other applications-employed in formulations for removal of industrial slime- in research for generation of protoplast- for generation of antibacterial chitooligosaccharides (used in food preservation)

Challenges in cellulase research

Cellulase production is not cost effective

less efficient in conversion of natural lignocellulosic material to essential metabolites

Current commercial preparation of cellulose is economically not feasible

Major goals for future cellulase research

• Reduction in cost of cellulase production - optimizing growth conditions - lactose as an inducer of cellulase genes -use of mixed culture enhances production

•Genetic improvement of cellulase performance -Using cbh1 promoter of T.resei for over expression of cellulases

ReferencesR. K. Sukumaran, Reeta Rani Singhania and

Ashok Pandey (2005). Microbial cellulases – Production, applications and challenges. Journals of Scientific & Industrial Research 64: 832-844

K. Reczey, Zs. Szengyel, R. Eklund & G. Zacchi (1996). Cellulase Production by T. Reesei. Bioresource Technology 57: 25-30

Bhat M K & Bhat S (1997). Cellulose degrading enzymes and their potential industrial applications. Bioethanol Adv 15: 583-620

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