Cellulase-free xylanases fromBacillusand other microorganisms

Abstract

Xylanases are used mainly in the pulp and paper industries for the pretreatment of Kraft pulp prior to bleaching to minimize use of chlorine, the conventional bleaching agent. This application has great potential as an environmentally safe method. Hydrolysis by xylanases of relocated and reprecipitated xylan on the surface of cellulose fibres formed during Kraft cooking facilitates the removal of lignin by increasing permeability to oxidising agents. Most of the xylanases reported in the literature contained significant cellulolytic activity, which make them less suitable for pulp and paper industries. The need for large quantities of xylanases which would be stable at higher temperatures and pH values and free of cellulase activity has necessitated a search for novel enzymes. We have isolated and characterised several xylanase-producing cultures, one of which (an alkalophilic Bacillus SSP-34) produced more than 100 IU ml⁻¹ of xylanase activity. The SSP-34 xylanases have optimum activity at 50°C in a pH range 6–8, with only small amounts of cellulolytic activity (CMCase (0.4 IU ml⁻¹, pH 7), FPase (0.2 IU ml⁻¹, pH 7) and no activity at pH 9).