HEMICELLULOLYTIC ACTIVITY IN THE CROP RESIDUES

Abstract

The hemicelluloses are polysaccharides which prevail in close association with cellulose, These are constituents of the primary as well as secondary cell walls and form a bridge between pectic and cellulosic fractions. Hemicelluloses are one of the major constituents added to the soil, second only in quantity to cellulose and these consequently represent a significant source of energy and nutrients to the microflora. From time to time Several views have been given by scientists on the chemistry, biochemistry and microbial breakdown of hemicelluloses. A majority of fungi are known to be capable of degrading hemicelluloses and utilizing as C-source. All main groups of fungi are able to decompose hemicelluloses. A complete degradation of xylans requires the joint action of different enzymes including (i) endoxylanase: which attacks the xylan backbone to produce substituted and non-substituted shorter oligomers (xylobiose and xylose). );(ii) exoxylanase or β-xylosidase: converts oligomers to xylose; (iii) α-D-glu-curonidase: liberates 4-o-methylglucuronic acid from 4-o-methyl glucuronic acid-substituted xylo-oligomers; (iv) α-L- arbinofuranosidase : hydrolyses non-reducing a-L-arabinofuranosyl groups of α-L-furanosides arabinans, arabinoxylans, and arabinogalactans;(v) acetyl-xylan esterase: deacetylates xylan. The capability of a microorganism to grow by utilising hemicellulose as sole C-source is usually taken as an index of hemicellulolytic ability.