Thermastable And Alkaline Xylanase From An Alkaliphilic Actinomycete

A xylanase producing alkaliphilic actinomycet~ strain designated As-19 was isolated from Lake rnAbjata, an alkaline Soda Lake in Ethiopia. The strain prodnce xylanase in solid state fermentationrn(SSF) using different agricultural residues (wheat bran, sugarcane bag ass, and saw dust) asrnsubstrates without enrichment of the medium .The highest level of enzyme was produced inrnwheat bran (165 U/g). Maximum production of xylanase was observed at wheat bran-tomoisturingrnagent ratio of I: 1. 5 (w/v) at 37°C for 72 h. Birch wood xylan enhances enzymernproduction with 110 % while xylose, aribinose, glucose, lactose and flUctose strongly repressedrnthe enzyme production. In the presence of metal ions such as HgCIz, and, ZnS04 the activity ofrnthe enzyme was strongly inhibited. Birch wood xylan was hydrolyzed more rapidly than oat speltrnxylan. The optimum pH of the enzyme was 8.5-10 and stable at alkaline pH (8-10). The optimumrntemperature for enzyme activity was 70-80 °c at pH 9. The enzyme after 4 h incubation retainedrn77.7 and 54 % of its original activity at 75 and 80°C respectively, at pH 9. The enzyme is alsornstable over wide temperature range (50-80°C) for I h at pH 9. Thus, the result showed that thernenzyme is both alkaline and thermostable. The enzymatic products of xylan hydrolysis were arnseries of shOtt-chain xylooligsaccharides, indicating the enzyme was an endoxylanase. These arernsome characteristics that make this enzyme potentially very attractive for industrial applications.rnrnKey words: Actinomycete; xylem; xylanase; alkaliphile.

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