Biotechnology and Bioprocess Engineering 2019; 24(5): 810-817  
Construction and Application of Low Cellulase-producing Bacillus licheniformis Strains for Bio-pulping of Bamboo
Le Xue1,2,†, Haihong Han2,†, Han Fan1,2, Piwu Li1,2, Tengfei Wang1,2, Jing Xiao1,2, Ruiming Wang1,2, and Junqing Wang1,2
1State Key Laboratory of Biobased Material and Green Papermaking (LBMP), Jinan 250353, Shandong, China
2Key Laboratory of Shandong Microbial Engineering, QILU University of Technology (Shandong Academy of Sciences), Jinan 250353, Shandong, China
Correspondence to: Junqing Wang
State Key Laboratory of Biobased Material and Green Papermaking (LBMP), Jinan 250353, Shandong, China
Tel: +86-0531-89631138; Fax: +86-0531-89631138
E-mail: wjqtt.6082@163.com

Le Xue and Haihong Han, the two first authors, contributed equally to this work.
Received: December 27, 2018; Revised: March 17, 2019; Accepted: March 19, 2019; Published online: October 31, 2019.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
To prevent cellulose loss during bio-pulping, two cellulase genes in Bacillus licheniformis 20085 were knocked out by homologous exchange technique. An engineering strain B. licheniformis 20085Δcelb was significantly compromised the ability to disintegrate filter paper compared to the original strain. After fermentation for 60 h, the CMCase activity value decreased from 1.86 to 0.50 U/mL, suggesting that the celb gene played an important role in the process of cellulose degradation in B. licheniformis 20085. We also assessed the ability of B. licheniformis 20085Δcelb to pulp bamboo. The yield of bamboo pulp was 51.91%, the kappa number was 11.26%, and 1.3% of cellulose was degraded after bio-pulping. Environmental Scanning Electron Microscope (ESEM) studies were also conducted to visualize the effect of these strains on bamboo cell walls. These results indicate that pulping with B. licheniformis 20085Δcelb can generate a higher yield and lower kappa number.
Keywords: B. licheniformis, bio-pulping, gene knockout, enzymatic hydrolysis, environmental scanning electron microscope


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