Production of thermostable cellulase-free xylanase by Clostridium absonum CFR-702

The production of cellulase-free thermostable xylanase was investigated wit h a locally isolated and identified strain, Clostridium absonum CFR-702 in a defined medium under anaerobic cultivation conditions at higher temperatu res (above 65 degreesC). Different fermentation conditions were standardise d for the growth and xylanase activity, the optimum being 72-96 h growth at pH 8.5, and cultivation temperature at 75-80 degreesC. Among different car bon sources tested, cellobiose, lactose, melezitose, raffinose, mannitol, s orbitol, myo-inositol, starch, pectin, cellulose and carboxymethyl cellulos e (CMC) did not support any growth and enzyme activity. Xylan and xylose in duced xylanase activity whereas xylobiose had less pronounced effect. The h ighest enzyme activity of 4300 nkatal per mi was obtained with birch wood x ylan (BWX) followed by larchwood xylan (LWX) and oatspelts xylan (OSX). Glu cose and beta -methyl xyloside (beta MEX) reduced the activity. Cultivation of the strain in 1000 mi of Hungate bottles with 1% birchwood xylan at 75 degreesC and pH 8.5 exhibited the highest enzyme activity of 7025 nkatal pe r mi without filter paper degrading CMC-ase and beta -glucosidase activitie s. Corn cob could also be utilised as a carbon source for economical produc tion of xylanase by C. absonum CFR-702. (C) 2000 Elsevier Science Ltd. All rights reserved.