Bioelectrocatalytic Refining of Lignin Fragments Using a Bioinspired -Etherolytic Bioanode

The biological depolymerization of lignins has been intensively studied to develop selective and ecofriendly processes for upgrading lignin toward the production of aromatic-based fine chemicals. However, the degradation of these aromatic polymers leads to heterogeneous mixtures of aromatic oligomers, limiting their industrial valorization. The etherolytic pathway of the soil probacterium Sphingobium paucimobilis, which acts like a "metabolic funnel" to refine the heterogeneous "soup" of low-molecular-mass lignin-derived compounds, involves enzymes called "Lig", which consist of NAD-dependent dehydrogenases and beta-etherases. The application of these Lig enzymes is a promising route for the development of biotechnologies for lignin valorization, but it is limited by the necessity of regenerating the NAD cofactor and the need to separate products from enzymes. In order to overcome these limitations, we have designed a bioelectrochemical system combining in situ electrochemical regeneration of the NAD(+) cofactor with the immobilization of five enzymes on a single electrode surface capable of catalyzing the specific beta-etherolysis of the beta-O-4 ether aryl bond. The bioelectrocatalytic ability of this beta-etherolytic bioelectrode to specifically cleave beta-ether bonds has been evaluated with a substrate model. We demonstrate that a racemic mixture of an aromatic dimer can be refined to homogeneous products with an efficiency of 22% per hour.