CELLULOLYTIC ACTIVITY IN MICROORGANISMS

Abstract

Cellulose is the most abundant polysaccharide occurring in plant materials. Thecellulose content of higher plant is never fixed and the concentration changes withthe age and type of the plant. It is specially predominant in woody substances aswell as in straw, stubble and leaves. Cellulose molecules are linear polymers(unbranched long chains) of β-D-glucopyranose residues linked by β(1, 4)-glycosidicbonds. The residues in the cellulose chain are stabilized by hydrogen bonds betweenhydroxyl groups of adjacent glucose residues. Cellulose is soluble in acids butinsoluble in alkaline solutions. Cellulose-decomposing microorganisms are foundabundantly in nature. Due to cellulolytic potential these play an important role inthe carbon cycle by recycling CO2 fixed through photosynthesis. Cellulose-decomposing microbes include a variety of aerobes and anaerobes; mesophiles aswell as thermophiles. Fungi and bacteria, however, are mainly responsible forcellulose degradation in nature. The details of the mechanism involved in thebreakdown of cellulose have been the subject of investigation for a long time. As percurrently accepted three-enzyme group hypothesis, the complete degradation ofnative cellulose to glucose requires three enzymes - (a) endo-β-1, 4-glucanase (EG) orcellulase (CEL, EC 3.2.1.4); (b) Cellobiohydrolase (CBH, or exo-glucanase, EC3.2.1.91) and (c) β-glucosidase (BG, EC 3.2.1.21). EG first hydrolyses amorphousregions of cellulose fibrils. The non-reducing ends thus generated are then attackedby CBH thereby releasing cellobiose. The action of CBH then proceeds into thecrystalline region. BG hydrolyses cellobiose to glucose. These enzymes worksynergistically to hydrolyse cellulose..The cellulolytic activity of microbes is greatlyaffected by different factor viz. availability of nutrients, optimum pH, temperatureand moisture contents have been found to be a major controlling factor in theproduction of cellulolytic enzymes