Mutagenesis of Alkalophilic Cellulosimicrobium sp. CKMX1 for Hyper-Production of Cellulase-Free Xylanase in Solid State Fermentation of Apple Pomace

Abstract

Cellulosimicrobium sp. CKMX1 isolated from mushroom compost, produced extracellular endo-1,4-β-xylanase (EC 3.2.1.8) at 35 °C and pH 8.0. In this study the wild strain of Cellulosimicrobium sp. CKMX1 was improved for enhanced xylanase production by using physical mutagen i.e. ultraviolet rays and chemical mutagens i.e. ethidium bromide (0.1–2.0 mg/ml) and ethyl methanesulfonate (5–70 mg/ml). Mutant (E5) with hyper xylanase production was obtained after treating wild strain with ethyl methanesulfonate on the basis of xylanase activity index and xylanase activity in liquid medium. Mutant E5 (568 U/g dry bacterial pomace) resulted in 35.89 % increase over wild strain (418 U/g dry bacterial pomace) in xylanase activity in solid state fermentation under optimized conditions. Further optimization of enzyme production by Cellulosimicrobium sp. CKMX1 mutant, E5 was carried out using central composite design following response surface methodology with four independent variables (yeast extract, ammonium nitrate, Tween 20 and carboxymethyl cellulose), which resulted in further increase of 1.63-fold in xylanase production (927.65 U/g dry bacterial pomace).The effectiveness of cellulase-free hyper xylanase producing mutant E5 to work in alkaline conditions indicates its possible applicability in paper and pulp industry.