Saifullah Khan, Fariha Hasan, Samiullah Khan, Aamer Ali Shah
Department of Microbiology,Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad 45320, Pakistan
A bacterium, designated as strain K-22 was isolated from GaramChashma, Manghopir, and Karachi that produced xylanase enzyme when cultured on nutrient agar supplemented with birch wood xylan, as indicated by clear zone of hydrolysis (2.0 cm) around its growth. The bacterium was identified as Bacillus pumilus with 99% similarity with type strain D4H3. Strain K-22 produced maximum amount of enzyme at 37°C, pH 8, 0.4% xylan concentration, 3% inoculum and 2% salt concentration. Xylanase enzyme was purified to homogeneity by column chromatography as indicated by a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with size of approximately 78 kDa. The enzyme was stable at 20 to 70°C (with an optimal temperature 50°C) and in a pH range of 5.0-10 (with an optimal pH of 8.0). It was stable in the presence of various metal ions such as Mn+2, Ca+2, and Mg+2 while Zn+2, Cu+2 and Hg+2 inhibited the activity. Xylanase activity was also inhibited by chemical reagents such as EDTA, SDS, PMSF, and Marcaptoethanol while NaCl and Sodium azide had very little effect on xylanase activity. Hence it is concluded, that xylanase purified from Bacillus pumilus strain K-22 can be useful in various industrial applications.
Keywords:Bacillus pumilusstrain K-22, xylanase, columnchromatography, SDS-PAGE, characterization.