Degradation and Transformation of Lignin by a Fungus Aspergillus Flavus Strain F-1

Abstract

<strong>Background:</strong> Lignin is the largest natural aromatic polymer in nature and is also a unique aromatic-based biopolymer, accounting for nearly 30% of the earth's organic carbon. Generally, lignin is regarded as waste and is mainly used as a lowvalue fuel that is burned to generate heat and energy to solve the problem of biomass waste; for this obstacle of lignin, highly efficient biodegradation plays a critical role in developing an environmentally friendly technique for lignin biotransformation.<br /><strong>Objectives:</strong> This study intends to isolate and purify several microbial strains from nature. It also explores how their lignin degradation is able to enhance the biodegradation and recycling of biomass and the reclamation of lignin in wastewater from pulp and paper mills.<br /><strong>Materials and Methods:</strong> Lignin-degrading microbial strains were isolated from soil using medium containing sodium lignosulphonate as the sole carbon source. They were then screened by aniline blue and guaiacol plate, and then the best strain was chosen and identified. The conventional one-factor method was used to optimize various parameters that affect lignin's degradation ability.<br /><strong>Results:</strong> The strain possessing the highest lignin biodegradation ability was identified and denominated as Aspergillus flavus F-1. After optimization, the maximum degradation rate of lignin, 44.6% within 3 days, was obtained at pH 7.0, 30 ℃, 2.5 g·L-1 ammonium sulfate, 2 g·L-1 lignin and 0.5 g·L-1 glucose. The results show the LiP and Lac secreted from Aspergillus flavus F-1 played the main role in the degradation of lignin.<br /><strong>Conclusions:</strong> One microbial strain, Aspergillus flavus F-1, was successfully isolated with a lignin-degrading ability that can cut the lignin into fragments. This provides a promising candidate for the transformation and utilization of crop waste biomass for various industrial purposes.