Rhamnolipid enhanced beta-glucosidase from Paenibacillus sp. LLZ1 for in situ lignocellulose saccharification in ionic l
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ORIGINAL ARTICLE
Rhamnolipid enhanced beta-glucosidase from Paenibacillus sp. LLZ1 for in situ lignocellulose saccharification in ionic liquids Xuemei Yao 1 & Lei Xiao 2 & Hang Liu 1 & Min Zhou 1 & Zheng Zhou 1 & Xin Ju 1
&
Liangzhi Li 1
Received: 30 May 2020 / Revised: 28 August 2020 / Accepted: 10 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Low β-glucosidase activity and stability are challenging limitations for the in situ saccharification of lignocellulose pretreated by ionic liquids. The addition of 0.1% (v/v) rhamnolipid, an ionic biosurfactant, was found to enhance the activity of β-glucosidase from Paenibacillus LLZ1 by 39% through a synergistic effect with 5% [Emim]OAc. The concentration of [Emim]OAc was further optimized to 2.5% (v/v) obtaining as high as 48% PsBGL activity increase. Fluorescence and near-UV circular dichroism spectroscopy analyses revealed looser protein structure and more hydrophilic microenvironment in the system of rhamnolipid and [Emim]OAc. Though ILs showed deactivation effect on cellulases, rhamnolipid was speculated to alleviate protein denaturation significantly. The reaction system was further applied in the hydrolysis of cellobiose and bagasse cellulose. The conversion was increased by 33% for cellobiose and by 62% for bagasse cellulose, demonstrating the application potential of the reaction system. The improvement was attributed to both reduced cellobiose inhibition and effective substrate solubilizing, and the latter was monitored by scanning electron microscopy to show the morphological change of substrates directly. This study proved the effect of surfactant in in situ enzymatic saccharification of lignocellulose and provided a practical enzymatic hydrolysis system. Keywords β-Glucosidase . Paenibacillus LLZ1 . Lignocellulose . Ionic liquid . Rhamnolipid . Synergistic effect
1 Introduction Conversion of ubiquitous lignocellulose efficiently and costeffectively towards renewable biofuels is of great importance for sustainable development and solving global climate change nowadays [1, 2]. Considering the compact crystalline structure of lignocellulose, pretreatment process is critical for various following utilizations. In the pretreatment for cellulase hydrolysis, solubilization by ionic liquids (ILs) is an environmentally friendly method and has been studied extensively [3, Xuemei Yao and Lei Xiao contributed equally to this work. * Xin Ju [email protected] * Liangzhi Li [email protected] 1
School of Chemistry, Biology and Material Engineering, Suzhou University of Science and Technology, No.99 Xuefu Rd., Huqiu district, Suzhou 215009, Jiangsu Province, China
2
School of Statistics and Mathematics, Zhongnan University of Economics and Law, Wuhan 430064, People’s Republic of China
4]. The cooperation of IL pretreatment and enzymatic hydrolysis with the presence of ILs has been developed as the in situ enzymatic saccharification of lignocellulose [5]. The integrated process is regarded with high economic significance
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