Modification of lignin in sugarcane bagasse by a monocopper hydrogen peroxide-generating oxidase from Thermobifida fusca

- Open reading frame 1114 of T. fusca (Tfu1114) encodes a hydrogen peroxide-generating oxidase.
- Tfu1114 modifies the physicochemical properties of alkaline lignin.
- Tfu1114 liberates dilignol subunits from sugarcane bagasse.
- Tfu1114 helps cellulolytic enzymes to release usable reducing sugars from bagasse.

Agricultural lignocelluloses could represent great resources for the production of biofuels and renewable chemicals if the recalcitrant lignin polymer could be efficiently removed without negatively impacting the environment. Recently, a monocopper polyphenol oxidase (Tfu1114) from Thermobifida fusca was found capable of assisting the bacterium's own xylanase/cellulase to release reducing sugars from sugarcane bagasse. This study demonstrates that molecular oxygen was reduced to hydrogen peroxide by Tfu1114, coupled to the oxidation of 2,6-dimethoxyphenol, alkaline lignin, or sugarcane bagasse. Tfu1114 was able to reduce the total phenolic content of alkaline lignin and shift the molecular weight distribution to species with smaller sizes. Dilignol subunits such as syringaresinol and simulanol were generated in the hydrolysate of bagasse treated with Tfu1114. FTIR analysis suggests that Tfu1114 removed some CC and/or CO bonds adjacent to aromatic rings of lignin. From an applied perspective, Tfu1114 and cellulases acted in concert to release reducing sugars that were as usable as glucose for the cultivation of Escherichia coli, suggesting that toxins such as furfural and furan were absent, or at ignorable concentrations, in the hydrolysate. Tfu1114, therefore, represents a new type of lignin-degrading enzyme with potential to provide an eco-friendly way to modify the lignin in lignocellulose.

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