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Microbial Production of Lignin-Degrading Enzymes from Genetically Engineered Aspergillus Nidulans and Enzymatic Depolymerization of Lignin

Enshi Liu, University of Nebraska - Lincoln


Development of economic and sustainable energy technologies that could alter our reliance on petroleum-based products to renewable substitutes has been constantly facilitated by the increasing environmental concerns. Conversion of lignocellulosic biomass to value-added products is considered as a promising approach to shift our energy dependence. Lignin valorization plays a central role in biorefining industry, as lignin is the most abundant natural source of renewable aromatic compounds. Currently, lignin is underutilized due to its recalcitrant nature and heterogeneity. Lignin depolymerization is a promising method to overcome the lignin heterogeneity and produce relatively uniform products for further upgrading. Particularly, enzymatic lignin depolymerization has received growing attention due to its selectivity and mild reaction conditions compared to thermochemical methods. However, it is still challenging to enzymatically depolymerize lignin due to the high cost and low yield production of lignin-degrading enzymes. Therefore, it is critical to develop cost-effective technologies to produce lignin-degrading enzymes. This research aims to produce two lignin-degrading enzymes, i.e. lignin peroxidase (LiP) and aryl alcohol oxidase (AAO), via heterologous protein expression in genetically modified Aspergillus nidulans. The AAO production medium was optimized by statistical design, and greatest AAO activity (1021 U/L) was achieved at 61.0 g/L maltose, 26.4 g/L CSL, and 13.8 g/L NaNO3. The AAO activity was further enhanced to 1906 U/L by process optimization in stirred-tank bioreactor. A novel LiP from Thermothelomyces thermophiles was expressed in recombinant A. nidulans. The LiP production medium was also optimized, and different fed-batch strategies were investigated to improve LiP production in stirred-tank bioreactor. A maximum LiP activity of 1645 mU/L was achieved by using multi-pulse fed-batch strategy. In addition, a novel and consolidated approach to effectively solubilize lignin and enzymatically depolymerize lignin by a bi-enzyme system containing LiP and AAO in aqueous biocompatible ionic liquid was developed and evaluated. Results demonstrated that the bi-enzyme system can reduce the molecular weight of lignin in both solid and liquid phases and no exogenous H2O2 was required.

Subject Area

Bioengineering|Agricultural engineering|Microbiology|Energy|Sustainability|Chemical engineering|Thermodynamics

Recommended Citation

Liu, Enshi, "Microbial Production of Lignin-Degrading Enzymes from Genetically Engineered Aspergillus Nidulans and Enzymatic Depolymerization of Lignin" (2020). ETD collection for University of Nebraska - Lincoln. AAI28259109.