Xylanase from thermotolerant Bacillus haynesii strain, synthesis, characterization, optimization using Box-Behnken Design, and biobleaching activity

Abstract

AbstractThe economic value of xylanolytic enzymes is derived from their use in a variety of industrial processes, which necessitates a cost-effective manufacturing procedure. In the current study, forty bacterial isolates were isolated from water samples and investigate their efficacy to producing xylanase enzyme. The most potent bacterial isolate was identified by sequencing and amplifications of 16Sr RNA gene as Bacillus haynesii strain K6. The impacts of various culture conditions on the productivity of xylane were examined. Data showed that the highest xylanase production was achieved at pH 7, in presence of 3 g/L xylan, 5 g/L peptone, and incubated at 40 °C for 24 h. The Box-Behnken model was used to find the best parameters for the relevant variables, and the results revealed an increase in xylanase production with values of 35.02 U/mL. The maximum precipitation of xylanase from the optimized culture was attained by ammonium sulfate (60%) followed by purification using dialysis and sephadex G100 column chromatography. The purified xylanase had a 12-fold enrichment, with a specific activity of 84 U/mg and a molecular weight approximately 439 KDa determined by thin-layer chromatography (TLC)/mass spectrometry. The amino acid analysis of the purified xylanase enzyme revealed the presence of 15 amino acids, with the highest concentrations of 1940 and 1520 mg/L for proline and cysteine, respectively. Finally, the physical properties of wastepaper pulp were improved after treatment with xylanase enzyme. The whiteness and softness of xylanase-treated wastepaper were improved with percentages of 34.6% and 16.2%, respectively. Therefore, we recommend the use of xylanase enzyme in the bleaching process as it is a biologically synthetic material, safe, and suitable for industrial use, and it reduces the use of harmful chemicals.