Microbial lignin valorization is promising, yet the heterogeneity of aromatic compounds generated from lignin depolymerization remains a significant challenge. Here, we engineered Sphingobium lignivorans SYK-6 to funnel aromatic mixtures in black liquor from oxygen-soda-anthraquinone pulping into the polymer building block 2-pyrone-4,6-dicarboxylic acid (PDC). In softwood (Japanese cedar) black liquor, rich in guaiacyl-type aromatics, a PDC hydrolase gene-deficient strain (ΔligI) achieved a 135% (mol/mol) PDC yield based on identified compounds, suggesting conversion of unidentified aromatics, potentially including oligomers. Hardwood (birch) black liquor contains abundant syringyl-type aromatics metabolized via branched pathways in SYK-6. By identifying a previously unidentified catabolism gene (desY) and disrupting ligI, ligM, and desY, we redirected metabolic flux toward PDC, obtaining a 91% (mol/mol) PDC yield from syringic acid and 62% from birch black liquor. These results demonstrate the strong potential of engineered SYK-6 for efficient PDC production from diverse lignin streams through biological funneling.
Kamimura et al. (Tue,) studied this question.