Co-integration of laccase and xylanase from Bacillus pumilus into mini-cellulosome facilitates softwood sulfite pulp biobleaching and reduces hydrogen peroxide consumption

Biobleaching is an eco-friendly strategy that can reduce costs and pollution in the pulp and paper industry. Herein, an effective biobleaching approach was proposed using a novel multi-enzyme complex. The multi-enzyme complex was constructed based on mini-cellulosome scaffolding protein integrated with laccase (BpLac) and xylanase (BpXyn) from Bacillus pumilus. The influence of different parameters on the multi-enzyme complex assembly was investigated. The multi-enzyme complex performed better than the free enzyme cocktail in softwood sulfite pulp bleaching. Specifically, free enzyme cocktail treatment decreased the kappa number from 12.2 to 9.1 and increased the brightness from 39.79 to 41.57 % ISO. With more phenolics and reducing sugars releases, the multi-enzyme complex treatment further decreased the kappa number to 8.7 and increased the brightness to 42.09 % ISO. The bleaching performance of the multi-enzyme complex could be further improved at 50 °C, pH 7.0, and 6 % pulp consistency. Measurement of the tensile strength, breaking length, and tearing index suggested that the multi-enzyme complex treatment would not damage fibers in the pulp. Moreover, the multi-enzyme complex treatment could reduce the consumption of H₂O₂ by 40 % in subsequent chemical bleaching. Therefore, utilizing the multi-enzyme complex in biobleaching is a promising way to advance a cleaner papermaking process.