Enhanced production, purification and characterisation of a novel cellulase-poor thermostable, alkalitolerant xylanase from Bacillus circulans AB 16

• Published in: Process biochemistry (1991) 2000-03, Vol.35 (8), p.849-856
• Main Authors: Dhillon, Ashita, Gupta, J.K., Khanna, S.
• Format: Article
• Language: English
• Subjects: Bacillus circulans; Purification; Thermophilic; Xylanase
• ISSN: 1359-5113; 1873-3298
• DOI: 10.1016/S0032-9592(99)00152-1

A thermophilic Bacillus circulans AB 16, isolated from a garbage dump produced novel extracellular cellulase-poor, thermostable xylanase in basal medium containing rice straw. The xylanase yield was enhanced more than two and a half fold in the presence of tryptone and other media modifications. The highest xylanase activity obtained in liquid culture was 55 IU/ml. Two xylanases Xyl A and Xyl B were purified to homogenity by Q Sepharose and Sepharose 6B chromatograph. Xyl A ( M r 30 000) had a pH optima of 6 and a temperature optima of 75–80°C, while Xyl B ( M r 22 000) also had a pH optima of 6 but with a temperature optima of 65–70°C. Both Xyl A and Xyl B had a pH optima of 6 but retained 46% activity at pH 8. Xyl A retained 70% activity at 65°C, pH 9 and 2 h incubation while Xyl B retained 34% under the similar conditions. Both Xyl A and Xyl B showed 90% inhibition in activity by 1 mM Hg 2+. The hydrolysis pattern of Xyl A yielded mainly xylobiose with lower amount of xylo-oligosaccharides and xylose while Xyl B yielded mainly higher oligosaccharides with lesser amounts of xylobiose and negligible amounts of xylose. The crude enzyme from B. circulans AB 16 showed higher chromophore release of 0.360 U as compared to Xyl A and Xyl B with a chromophore release of 0.115 and 0.069 units and thus would be more useful for pulp bleaching than purified xylanases.