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Abstract
The protoplast fusion technique was applied to construct a more efficient engineering microbial strain to degrade lignin by fusing two strains, Pseudomonas putida and Gordonia sp. At an initial lignin concentration of 900 mg/L, COD, BOD, TOC removal efficiencies increased from 69–76%, 69–72%, and 70–72% by the parent stains to 83%, 83%, and 83% of the fused strain, respectively. IR and HPLC analyses of the treated solution suggested that the fused strains were more capable of breaking the Cα–Cβ bonds of the benzene ring in lignin compared to its parent strains, yielding syringyls as the main product. GC–MS analysis was used to identify the release of three-types of lower molecular intermediates: ring-opening, monomer, and dipolymer products. The phenolic hydroxyl group in lignin was oxidized to carbonyls, followed by further degradation to acids and esters. The carboxyl group on the ether linkage that maintains the macromolecular structure of lignin was oxidized to acyls, which further led to depolymerization and the opening of benzene ring.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. The research was financially supported by grants from Guangdong Province Science and Technology Project (No: 2013B090200016, 2013B021000008 and 2015B020215007), Joint fund of Guangdong Province (NO: U1401235) and Major Science and Technology Program for the Industry-Academia-Research Collaborative Innovation of Guangzhou. The authors are grateful to the kind support from the Committee of the 4th Conference on Biorefinery towards Bioenergy (ICBB2013) in Xiamen, China.