Effective utilization of magnetic nano-coupled cloned beta-xylanase in saccharification process

The beta-xylanase gene (DCE06_04615) with 1041 bp cloned from Thermotoga naphthophila was expressed into E. coli BL21 DE3. The cloned beta-xylanase was covalently bound to iron oxide magnetic nanoparticles coated with silica utilizing carbodiimide. The size of the immobilized MNPs (50 nm) and their binding with beta-xylanase were characterized by Fourier-transform electron microscopy (FTIR) (a change in shift particularly from C-O to C-N) and transmission electron microscopy (TEM) (spherical in shape and 50 nm in diameter). The results showed that enzyme activity (4.5 +/- 0.23 U per mL), thermo-stability (90 degrees C after 4 hours, residual activity of enzyme calculated as 29.89% +/- 0.72), pH stability (91% +/- 1.91 at pH 7), metal ion stability (57% +/- 1.08 increase with Ca2+), reusability (13 times) and storage stability (96 days storage at 4 degrees C) of the immobilized beta-xylanase was effective and superior. The immobilized beta-xylanase exhibited maximal enzyme activity at pH 7 and 90 degrees C. Repeated enzyme assay and saccharification of pretreated rice straw showed that the MNP-enzyme complex exhibited 56% +/- 0.76 and 11% +/- 0.56 residual activity after 8 times and 13 times repeated usage. The MNP-enzyme complex showed 17.32% and 15.52% saccharification percentage after 1(st) and 8(th) time usage respectively. Immobilized beta-xylanase exhibited 96% residual activity on 96 days' storage at 4 degrees C that showed excellent stability.