An alkali-thermostable xylanase from Bacillus pumilus functionally expressed in Kluyveromyces lactis and evaluation of its deinking efficiency.

This work aimed at studying the recombinant expression of an alkali- and thermo-stable xylanase from Bacillus pumilus in Kluyveromyces lactis and its use in deinking of civic paper waste. Efficient expression with a 3-fold increase in the activity than the native organism was achieved. An inducer concentration of 2.5% and medium pH of 9.0 was the best for enzyme expression. Purified enzyme showed an optimum activity at temperatures 50 and 60°C and pH 9.0 and 10.0, respectively. At pH 12.0, enzyme retained 74% and 26% activity after 2 and 3h of incubation, respectively. After incubation at 50 and 60°C for 1h, the enzyme showed 100% retention of activity, and remained active for 4h at 60°C retaining 23% residual activity. Partially purified recombinant enzyme showed higher deinking efficiency (273%) of laser print waste paper than crude xylanase from Bacillus and commercial acidic enzyme. This xylanase with superior stability characteristics could be a suitable candidate in paper and pulp industries.