Xylanases ofBacillusspp. isolated from ruminant dung as potential accessory enzymes for agro-waste saccharification

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Polysaccharide hydrolase producing bacteria were isolated for biomass saccharification step in two-step bioethanol production. Xylanolytic bacteria were found to be common in ruminant dung. Seven Bacillus dung isolates exhibited high xylanolytic activity; three of which were identified as Bacillus safensis and four as Bacillus altitudinis, based on 16S rDNA and gyrB gene sequencing. Interestingly, comparison of activity profiles for B. safensis M35 and B. altitudinis R31 and J208 crude xylanases showed activity in similar temperature and pH ranges of 40–60 °C and 6·0–9·0, respectively, even though they were isolated from three different dung sources. Furthermore, 22–28% viscosity reduction of beechwood xylan substrate by all the three xylanases points towards their endo-acting nature. Endo-acting xylanases are envisaged as accessory enzymes which help expose the cellulose fibres for the subsequent action of the core enzyme cellulases. In this study, when supplemented to the commercial cellulase as a cocktail, the accessory role of the crude xylanases from the selected Bacillus strains was established as 1·3, 2·33 and 1·9 fold increase in saccharification of barley husk, sugarcane bagasse and wheat husk was achieved, respectively.

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