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-Larbinofuranosidase : 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.

Key words: Hemicellulose, Xylan, Xylanases, Microorganisms, Hemicellulolytic index