Cellulase-free-thermo-alkali-solvent-stable xylanase from Bacillus altitudinis DHN8: Over-production through statistical approach, purification and bio-deinking/ bio-bleaching potential

Abstract

The present study shows over-production of cellulase-free xylanase using Bacillus altitudinis DHN8 followed by its purification and applications. Response surface methodology, especially Box-Behnken Design was used to improve the enzyme yield by optimizing submerged fermentation conditions. Statistically optimized fermentation conditions to achieve higher xylanase production (492 IU/mL) were sorghum straw 1.0%, inoculum size 3.0%, incubation time 48 h, temperature 32 °C, agitation speed 200 rpm and gelatin 0.37%. Under these conditions, the resulted enzyme activity was two-fold high compared to the activity (245 IU/mL) resulted after one-factor-at-a-time optimization. The purified xylanase was of high molecular weight (~98 kDa) as revealed by SDS-PAGE. It showed optimum activity between 45 °C and 55 °C and at pH 8.0. Various metals, modulators, and organic solvents further improved the activity of purified enzyme. In this study, the crude xylanase was used for (1) bio-deinking of hand-written office waste papers having blue ink and (2) bio-bleaching of carton pulp. In the first case, 56.3% deinking of waste papers was achieved whereas in the second case, Kappa number of carton pulp was reduced to 10.85. Both results are suggesting the potential of B. altitudinis xylanase for the bio-deinking and bio-bleaching.