Modification of Different Pulps by Homologous Overexpression Alkali-Tolerant Endoglucanase in Bacillus subtilis Y106

Meimei Wang,Daolei Zhang,Jian Du,Xuezhi Li,Jian Zhao

doi:10.1038/s41598-017-03215-9

Abstract

Cellulase (mainly endoglucanase, EG) has been used in pulp modification for improving paper quality through environmentally friendly process. But low activity in alkaline pH and high filter paper activity (FPA) were still obstacles for extending the cellulase application in papermaking industry. In the study, an alkali-tolerant EG gene of Bacillus subtilis Y106 was homologous over-expressed for obtaining suitable enzyme used in pulp modification. The engineering strain could produce the crude enzyme with more alkali-tolerant EG and little PFA. Potential of the crude enzyme in modification of different pulps were investigated. It was found that the enzyme could be used for improving drainage and strength properties of pulps from softwood, hardwood and non-wood materials, especially non-wood pulp such as wheat straw pulp. The underlying mechanisms of pulp modification and different effects on various types of pulps by the EG treatment were also discussed by studying the change in fibers characteristics and fiber bonding.

Highlights

Enzymes-assisted modification comply such restrictions that lower costs and environmentally friendly for improving the strength properties of pulp
EG made less damages to pulp properties and more suitable for pulp modification compared to the cellulase with high filter paperactivity (FPA) that contained CBH caused excessive degradation of cellulose[10,11,12]
The results indicated that the EG treatment was more helpful to improve the strength properties of hardwood pulp and non-wood pulp compared with softwood pulp

Summary

Introduction

Enzymes-assisted modification comply such restrictions that lower costs and environmentally friendly for improving the strength properties of pulp. Oksanen et al (2000) treated the recycled kraft pulps with cellulase (EGI, EGII) from Trichoderma reesei and found that EGs treatment significantly improved pulp drainage already at low dosage levels[17]. Some problems such as low enzyme activity in alkaline range of pH, unreasonable enzymatic system such as high filter paper activity (FPA), limited the cellulase application in pulp modification. We attempted to obtain the enzyme with high EG activity and low FPA in alkaline pH value by homologous expressing alkali-tolerant endoglucanase for promoting the commercial applicability of Bacillus subtilis Y106. Using three types of pulps from softwood, hardwood and non-wood respectively as substrates, we evaluated the potential of the recombinant EG in the pulps modification and discussed possible causes about the differences in enzymatic modification of different pulps

Methods

Results

Conclusion