Synergistic Treatment of Alkali Lignin via Fungal Coculture for Biofuel Production: Comparison of Physicochemical Properties and Adsorption of Enzymes Used As Catalysts

Ruhong Luo,Ao Xia,Qiang Liao,Xianqing Zhu,Zhichao Deng,Xun Zhu,Yun Huang

doi:10.3389/fenrg.2020.575371

Abstract

White-rot fungi (WRF) is capable of producing extracellular enzymes that degrade lignin structure and facilitate biofuel production from lignocellulosic biomass wastes. However, fungal monocultures are constrained by low activities of the lignin-degrading enzyme system, leading to poor treatment efficiency and a long duration, which are not advantageous for large-scale applications. To improve enzyme production and enhance lignin degradation, a novel coculture system was proposed using the white-rot fungi Phanerochaete chrysosporium and Irpex lacteus CD2. The degradation efficiency of the alkali lignin by the fungal coculture was 26.4%, which was higher than that of the fungal monocultures. It was due to the production of lignin degrading enzymes was promoted in the liquid medium. Scanning electron microscopy (SEM), fourier transform infrared (FTIR), thermogravimetric (TG) and mercury porosimeter analyses results revealed that the alkali lignin treated with the fungal coculture had the largest porosity, and the degree of destruction of the alkali lignin structure by the fungal coculture was higher than that of the fungal monocultures. Meanwhile, the nonproductive adsorption of enzymes on alkali lignin was significantly reduced by 61.0% when the biomass was treated with the fungal coculture. As a result, the nonproductive adsorption was remarkably reduced, while it significantly improved the cellulase catalysis efficiency. These results demonstrated the synergistic effects of the fungal coculture for biomass treatment and provided a new approach for increasing lignin degradation while improving enzymatic catalysis and biofuel production through fungal coculture.

Highlights

Lignocellulosic biomass from agricultural residues is an abundant resource in China, with an annual productivity of 980 million tons, which is equal to approximately 490 million tons of coal (Isroi et al, 2011)
The innovation of this study is to propose a new coculture system of P. chrysosporium and I. lacteus CD2, based on their complementarity lignin degrading enzymes (LDEs), to treat alkali lignin as a model compound derived from lignocellulose biomass
The strains stored at 4°C were inoculated in fresh Potato dextrose agar (PDA) slant culture medium

Summary

Introduction

Lignocellulosic biomass from agricultural residues is an abundant resource in China, with an annual productivity of 980 million tons, which is equal to approximately 490 million tons of coal (Isroi et al, 2011). A mass of lignocellulosic biomass is incinerated in the field, it pollutes the environment and wastes many resources. Lignocellulose is mainly composed of three components: lignin, cellulose and hemicellulose. Cellulose and hemicellulose are polysaccharide structures that can be directly hydrolyzed by enzymes into available reducing sugars. The presence of lignin makes it difficult to directly utilize the polysaccharides in lignocellulosic biomass. The removal of lignin improves the accessibility of the polysaccharides, resulting in high biomass conversion efficiency and an economically feasible production process. Without an appropriate pretreatment method, only 20% of the theoretical maximum yield can be obtained by enzymatic hydrolysis (Suksong et al, 2020)

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