Depolymerization and conversion of lignin to value-added bioproducts by microbial and enzymatic catalysis

Abstract

Lignin, the most abundant renewable aromatic compound in nature, is an excellent feedstock for value-added bioproducts manufacturing; while the\xa0intrinsic heterogeneity and recalcitrance of which hindered the efficient lignin biorefinery and utilization. Compared with chemical processing, bioprocessing with microbial\xa0and enzymatic catalysis is a clean and efficient method\xa0for lignin depolymerization and conversion. Generally,\xa0lignin bioprocessing involves lignin decomposition to\xa0lignin-based aromatics\xa0via extracellular microbial enzymes and further converted to\xa0value-added bioproducts through microbial metabolism. In the review, the most recent advances in degradation and conversion of\xa0lignin\xa0to value-added bioproducts catalyzed by microbes and enzymes were summarized.\xa0The lignin-degrading microorganisms of white-rot fungi, brown-rot fungi, soft-rot fungi, and bacteria under aerobic and anaerobic conditions were comparatively analyzed. The catalytic metabolism of the microbial lignin-degrading enzymes of laccase, lignin peroxidase, manganese peroxidase, biphenyl bond cleavage enzyme, versatile peroxidase, and β-etherize was discussed. The microbial metabolic process of H-lignin, G-lignin, S-lignin based derivatives, protocatechuic acid, and catechol was reviewed. Lignin was depolymerized to\xa0lignin-derived aromatic compounds\xa0by the\xa0secreted enzymes of\xa0fungi and bacteria, and the\xa0aromatics were converted to\xa0value-added compounds through microbial catalysis and metabolic engineering. The review also proposes new insights for future work to overcome the\xa0recalcitrance of\xa0lignin and convert it to value-added bioproducts by microbial and enzymatic catalysis.