To detect natural laccase mediator, the extracellular culture fluid of Trametes versicolor laccase production medium was fractionated using degradation of anthracene which can not be degraded with laccase alone. As a result, 4-hydroxybenzoic acid (HBA) was isolated from the culture fluid, and it was clear that HBA acted as a natural mediator and the degradation efficiency of anthracene by laccase greatly increased. The laccaseHBA system could also oxidized the nonphenolic β-O-4 lignin model dimer to pruduce the Cα-oxidation, βether cleavage and aromatic ring cleavage products. The oxidation mechanisms of the laccase-HBA system are very similar to those for lignin peroxidase and laccase-1-hydroxybenzotriazol (HBT) system.

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The β–5 linkage is an intermolecular linkage in lignin. Sphingobium sp. strain SYK-6 can assimilate various lignin-derived dimers, including a β–5 dimer, dehydrodiconiferyl alcohol. In SYK-6, the hydroxyl group at Cγ of the B-ring side chain of dehydrodiconiferyl alcohol is oxidized to generate the γ-carboxylic compound, DCA-C. Then, the hydroxyl group at Cγ of the A-ring side chain of DCA-C is oxidized to the carboxyl group to generate the dicarboxylic compound, DCA-CC. The carboxylic group at Cγ of the A-ring side chain of DCA-CC is decarboxylated, and the accompanying spontaneous ether cleavage of the coumaran ring produces a stilbene-type compound, DCA-S. The conversions of DCA-C and DCA-CC are catalyzed by enantiospecific oxidases (PhcC and PhcD) and enantiospecific decarboxylases (PhcF and PhcG), respectively. DCA-S is subjected to cleavage of the interphenyl double bond by lignostilbene ɑ,β-dioxygenase to generate 5-formylferulate and vanillin. Among the eight lignostilbene ɑ,β-dioxygenase genes, vanillate-induced lsdD plays a critical role in cleaving DCA-S. The formyl group of 5-formylferulate is oxidized, and the resultant carboxylic group is subsequently decarboxylated to produce ferulate. Finally, ferulate and vanillin are further catabolized via a previously characterized pathway.

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A non-phenolic β-O-4-type lignin model compound, veratrylglycerol-β-guaiacyl ether (VG), was treated with H₂O₂ at high pH levels in our previous study. Veratraldehyde (Vald) and veratric acid (Vacid), which are non-phenolic analogues of the most common lignin-based fine chemicals, vanillin and vanillic acid, respectively, were obtained with a high total yield of 77% based on the amount of degraded VG, although only 22% of VG was degraded and hence the total yield of Vald and Vacid was only 17% based on the initial amount of VG. This study optimized the alkaline H₂O₂ treatment to enhance the degradation of VG and yields of Vald and Vacid. The degradation of VG and total yield of Vald and Vacid were enhanced from 22% to 54% and from 17% to 39%, respectively, by optimizing the conditions as follows: 1.96 mmol of H₂O₂ were added stepwise 400 times with an interval of 15 s in a reaction solution containing 1.0 mmol/L VG, 3.0 mol/L NaOH, 1.08 mmol/L FeCl3, and 3.24 mmol/L mannitol at 90℃. Doubling the reaction period and employing twice the amount of H₂O₂ (3.92 mmol) in the absence of mannitol further enhanced the degradation of VG to 61% and the total yield to 44%.

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