Decoding lignin valorization pathways in the extremophilic Bacillus ligniniphilus L1 for vanillin biosynthesis

The biggest challenge in the biological valorization of lignin is the achievement of a simple and effective route to produce fine chemicals through bacteria. In this study, system biology-guided biosynthesis of vanillin through lignin depolymerization using extremophilic Bacillus ligniniphilus L1 was investigated. As a result, the lignin metabolic network was elucidated. The position of vanillin as the central metabolite of lignin metabolism was confirmed in B. ligniniphilus L1. Genetic engineering of B. ligniniphilus L1 through knocking out vanillin dehydrogenase gene (vdh) to attenuate vanillin catabolism coupled with lignin pretreatment strategies has increased the vanillin titer by 28-fold (352 mg L− ). Moreover, a chassis cell milking approach has been successfully developed to debottleneck the cytotoxicity of vanillin. After seven fermentation cycles, vanillin yielded was found to be 1.95 μmol per mg cell dry weight, which was 7.6-fold more than the conventional fermentation. This study has demonstrated the biosynthetic platform for vanillin production and opens a promising avenue towards the cleaner production of valuable chemicals from lignin.