Thermastable and Alkaline Xylanase from an Alkaliphilic Actinomycete
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Date
2006-07
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Addis Ababa University
Abstract
A xylanase producing alkaliphilic actinomycet~ strain designated As-19 was isolated from Lake
Abjata, an alkaline Soda Lake in Ethiopia. The strain prodnce xylanase in solid state fermentation
(SSF) using different agricultural residues (wheat bran, sugarcane bag ass, and saw dust) as
substrates without enrichment of the medium .The highest level of enzyme was produced in
wheat bran (165 U/g). Maximum production of xylanase was observed at wheat bran-tomoisturing
agent ratio of I: 1. 5 (w/v) at 37°C for 72 h. Birch wood xylan enhances enzyme
production with 110 % while xylose, aribinose, glucose, lactose and flUctose strongly repressed
the enzyme production. In the presence of metal ions such as HgCIz, and, ZnS04 the activity of
the enzyme was strongly inhibited. Birch wood xylan was hydrolyzed more rapidly than oat spelt
xylan. The optimum pH of the enzyme was 8.5-10 and stable at alkaline pH (8-10). The optimum
temperature for enzyme activity was 70-80 °c at pH 9. The enzyme after 4 h incubation retained
77.7 and 54 % of its original activity at 75 and 80°C respectively, at pH 9. The enzyme is also
stable over wide temperature range (50-80°C) for I h at pH 9. Thus, the result showed that the
enzyme is both alkaline and thermostable. The enzymatic products of xylan hydrolysis were a
series of shOtt-chain xylooligsaccharides, indicating the enzyme was an endoxylanase. These are
some characteristics that make this enzyme potentially very attractive for industrial applications.
Key words: Actinomycete; xylem; xylanase; alkaliphile.
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Actinomycete