Microbial assimilation of lignin-derived aromatic compounds and conversion to value-added products

Efficient biological funneling of lignin into 2-pyrone-4,6-dicarboxylic acid via electrocatalytic depolymerization and genetically engineered Pseudomonas putida KT2440

Lignin has been an abundant biomass resource with remarkable potential to produce value-added chemicals. The comprehensive process from lignin degradation to the biological conversion of its monomers remains a challenge for demonstrating the industrial applicability of lignin refinery. Herein, Pseudomonas putida KT-PDCV overexpressing homologous vanillate-O-methylase (VanAB) could efficiently produce 2-pyrone-4,6-dicarboxylic acid (PDC) from lignin-derived compounds (LDC), including S-unit monomers (e.g., syringate and syringaldehyde). The engineered strain efficiently consumed syringate with other types of LDCs, such as p-coumarate and ferulate, and produced PDC up to 67.2 mM from mixed model lignin with a molar yield of 98 %. The efficient electrolyzer degraded practical lignin into the S-unit-dominant mixture of LDCs with remarkable performance. In addition, P. putida KT-PDCV directly utilized the mixture of LDCs without significant susceptibility to impurities, yielding a PDC of 0.91 mM with a molar yield of 62.3 %.

Recent advances in enzymes active on lignin-derived aromatic compounds

Lignin is an attractive alternative to fossil fuels as a feedstock for the sustainable manufacture of chemicals. Emergent strategies for lignin valorization include tandem processes whereby thermochemical fractionation of the biomass yields a mixture of lignin-derived aromatic compounds (LDACs), which are then transformed into target compounds by a microbial cell factory. Identifying LDAC-degrading pathways is critical to optimize carbon yield from diverse depolymerization mixtures. Characterizing enzymes - especially those that catalyze the rate-limiting steps of O-demethylation, hydroxylation, and decarboxylation - informs and enables biocatalyst design. Rational, structure-based engineering of key enzymes, as well as untargeted, evolution-based approaches, further optimize biocatalysis. In this review we outline recent advances in these fields which are critical in developing biocatalysts to efficiently synthesize lignin-based bioproducts.

Laboratory evolution in Novosphingobium aromaticivorans enables rapid catabolism of a model lignin-derived aromatic dimer

Lignin contains a variety of interunit linkages, leading to a range of potential decomposition products that can be used as carbon and energy sources by microbes. β-O-4 linkages are the most common in native lignin, and associated catabolic pathways have been well characterized. However, the fate of the mono-aromatic intermediates that result from β-O-4 dimer cleavage has not been fully elucidated. Here, we used experimental evolution to identify mutant strains of Novosphingobium aromaticivorans with improved catabolism of a model aromatic dimer containing a β-O-4 linkage, guaiacylglycerol-β-guaiacyl ether (GGE). We identified several parallel causal mutations, including a single nucleotide polymorphism in the promoter of an uncharacterized gene that roughly doubled the growth yield with GGE. We characterized the associated enzyme and demonstrated that it oxidizes an intermediate in GGE catabolism, β-hydroxypropiovanillone, to vanilloyl acetaldehyde. Identification of this enzyme and its key role in GGE catabolism furthers our understanding of catabolic pathways for lignin-derived aromatic compounds.IMPORTANCELignin degradation is a key step for both carbon cycling in nature and biomass conversion to fuels and chemicals. Bacteria can catabolize lignin-derived aromatic compounds, but the complexity of lignin means that full mineralization requires numerous catabolic pathways and often results in slow growth. Using experimental evolution, we identified an uncharacterized enzyme for the catabolism of a lignin-derived aromatic monomer, β-hydroxypropiovanillone. A single nucleotide polymorphism in the promoter of the associated gene significantly increased bacterial growth with either β-hydroxypropiovanillone or a related lignin-derived aromatic dimer. This work expands the repertoire of known aromatic catabolic genes and demonstrates that slow catabolism of lignin-derived aromatic compounds may be due to misregulation under laboratory conditions rather than inherent catabolic challenges.

Construction of versatile plastic-degrading microbial consortia based on ligninolytic microorganisms associated with agricultural waste composting

The accumulation of plastic in ecosystems is one of the most critical environmental concerns today. Plastic biodegradation using individual microbial cultures has shown limited success, which can be improved by employing microbial consortia with appropriate enzymatic capabilities. This study aims to assemble and characterize microbial consortia using ligninolytic fungi and bacteria isolated from an agricultural waste composting process, with the goal of enhancing the efficiency of plastic biodegradation. The compost microbiome demonstrated plastic-degrading functionality, particularly during the raw material and cooling phases. Ligninolytic microorganisms from compost were characterized for enzymes related to plastic degradation and their ability to colonize plastic films. The genera Bacillus, Pseudomonas, Fusarium, Aspergillus, Scedosporium, and Pseudallescheria exhibited a wide range of activities associated with plastic biodegradation, making them candidates for consortia assembly. The biodegradation of polyethylene using single and consortium cultures revealed that consortia, particularly those combining Bacillus subtilis RBM2 with Fusarium oxysporum RHM1, enhanced degradation efficiency. Additionally, consortia targeting multiple plastics, including virgin and recycled linear low-density polyethylene (LLDPE), polyethylene terephthalate (PET), and polystyrene (PS), showed varying levels of success, with bacterial-bacterial combinations such as Pseudomonas aeruginosa RBM21 and Bacillus subtilis RBM2 demonstrating broad-spectrum plastic degradation. These findings underscore the potential of compost-derived microorganisms for plastic biodegradation and suggest that utilizing microbial consortia offers a promising approach to tackling plastic pollution.

Comparative metagenomics reveals the metabolic flexibility of coastal prokaryotic microbiomes contributing to lignin degradation

Coastal wetlands are rich in terrestrial organic carbon. Recent studies suggest that microbial consortia play a role in lignin degradation in coastal wetlands, where lignin turnover rates are likely underestimated. However, the metabolic potentials of these consortia remain elusive. This greatly hinders our understanding of the global carbon cycle and the "bottom-up" design of synthetic consortia to enhance lignin conversion. Here, we developed two groups of lignin degrading consortia, L6 and L18, through the 6- and 18-month in situ lignin enrichments in the coastal East China Sea, respectively. Lignin degradation by L18 was 3.6-fold higher than L6. Using read-based analysis, 16S rRNA amplicon and metagenomic sequencing suggested that these consortia possessed varied taxonomic compositions, yet similar functional traits. Further comparative metagenomic analysis, based on metagenomic assembly, revealed that L18 harbored abundant metagenome-assembled genomes (MAGs) that encoded diverse and unique lignin degradation gene clusters (LDGCs). Importantly, anaerobic MAGs were significantly enriched in L18, highlighting the role of anaerobic lignin degradation. Furthermore, the generalist taxa, which possess metabolic flexibility, increased during the extended enrichment period, indicating the advantage of generalists in adapting to heterogenous resources. This study advances our understanding of the metabolic strategies of coastal prokaryotic consortia and lays a foundation for the design of synthetic communities for sustainable lignocellulose biorefining.

Revisiting alkali pretreatment to transform lignocellulose fermentation with integration of bioprocessible lignin

This study emphasized the synergistic production of bioprocessible lignin and carbohydrates during a sequential liquid hot water and alkali pretreatment of lignocellulose, facilitating their subsequent individual fermentation. Increasing the dose of alkaline lignin from 0 to 8 g/L inhibited cell growth in anaerobic digestion, with varying levels of inhibition observed in the following order: hydrolytic bacteria < acidogens < acetogens. Alkali pretreatment was adapted to maximize yields of bioprocessible lignin liquor without compromising utilization of the carbohydrates. Increasing the NaOH dose from 50 to 200 mg/g-feedstock monotonically improved lignin yields, but further increases in alkali loading led to a decline in lignin recovery. Volatile fatty acids production from anaerobic digestion of the carbohydrate moiety consistently increased with higher NaOH doses. The optimal conditions for maximizing lignin yields were determined to be 105 °C for 30 min, with NaOH loading in the range of 150-200 mg/g-feedstock, resulting in approximately 80 % lignin recovery, of which 35 % was biologically utilizable. Liquid hot water treatment prior to alkali pretreatment was confirmed as necessary to preserve carbohydrates of 0.1 g/g-feedstock at a low temperature of 70 °C. These findings are crucial for economically producing bioprocessible lignin without carbohydrate loss, a key step towards achieving full lignocellulose valorization.

Analysis of Straw Degradation and Whole Genome of Acrophialophora multiforma

Lignin is one of the main components in plants, which can transform value-added bioenergy and chemicals. At the same time, due to the close combination of lignin and hemicellulose in the structure, it becomes a barrier for cellulose utilization. Therefore, the effective degradation of lignin is of great significance for the utilization of these resources. In this study, the lignin degrading ability of Acrophialophora multiforma strain GZUIFR 22.397 was preliminarily investigated through straw degradation experiments and enzyme activity determination. Then, the whole genome of strain A. multiforma GZUIFR 22.397 was sequentially analyzed and annotated through multiple gene function annotation databases to comprehensively evaluate its lignin degrading potential. The results showed that the weight loss of straw reached 5.98 ± 3.95%. Laccase activity was 77.49 ± 2.65 U/L, lignin peroxidase activity was 160.57 ± 29.07 U/L, and manganese peroxidase activity was 294.83 ± 3.77 U/L. The genome of A. multiforma strain GZUIFR 22.397 spans 33.81 megabases and encompasses 9,370 genes. Among these, 6,122 genes have been annotated in the Gene Ontology (GO), 2,286 in the Cluster of Orthologous Groups of proteins (KOG), 2,283 in the Kyoto Encyclopedia of Genes and Genomes (KEGG), and 603 in the Carbohydrate Active enZYmes Database (CAZy). Concurrently, the genome analysis predicted the presence of 9 genes for laccase, 2 genes for lignin peroxidase, and 2 genes for manganese peroxidase. In summary, these results indicated that A. multiforma GZUIFR 22.397 has lignin degrading ability, and laid the foundation for deciphering the molecular mechanism of A. multiforma GZUIFR 22.397 to degrade lignin.

Lignin: An Adaptable Biodegradable Polymer Used in Different Formulation Processes

INTRODUCTION

LIG is a biopolymer found in vascular plant cell walls that is created by networks of hydroxylated and methoxylated phenylpropane that are randomly crosslinked. Plant cell walls contain LIG, a biopolymer with significant potential for usage in modern industrial and pharmaceutical applications. It is a renewable raw resource. The plant is mechanically protected by this substance, which may increase its durability. Because it has antibacterial and antioxidant qualities, LIG also shields plants from biological and chemical challenges from the outside world. Researchers have done a great deal of work to create new materials and substances based on LIG. Numerous applications, including those involving antibacterial agents, antioxidant additives, UV protection agents, hydrogel-forming molecules, nanoparticles, and solid dosage forms, have been made with this biopolymer.

METHODS

For this review, a consistent literature screening using the Pubmed database from 2019-2024 has been performed.

RESULTS

The results showed that there is an increase in interest in lignin as an adaptable biomolecule. The most recent studies are focused on the biosynthesis and antimicrobial properties of lignin-derived molecules. Also, the use of lignin in conjunction with nanostructures is actively explored.

CONCLUSIONS

Overall, lignin is a versatile molecule with multiple uses in industry and medical science.

Combined hemicellulolytic and phenoloxidase activities of Thermobacillus xylanilyticus enable growth on lignin-rich substrates and the release of phenolic molecules

Major challenge in biorefineries is the use of all lignocellulosic components, particularly lignins. In this study, Thermobacillus xylanilyliticus grew on kraft lignin, steam-exploded and native wheat straws produced different sets of phenoloxidases and xylanases, according to the substrate. After growth, limited lignin structural modifications, mainly accompanied by a decrease in phenolic acids was observed by Nuclear Magnetic Resonance spectroscopy. The depletion of p-coumaric acid, vanillin and p-hydroxybenzaldehyde combined to vanillin production in the culture media indicated that the bacterium can transform some phenolic compounds. Proteomic approaches allowed the identification of 29 to 33 different hemicellulases according to the substrates. Twenty oxidoreductases were differentially expressed between kraft lignin and steam-exploded wheat straw. These oxidoreductases may be involved in lignin and aromatic compound utilization and detoxification. This study highlights the potential value of Thermobacillus xylanilyticus and its enzymes in the simultaneous valorization of hemicellulose and phenolic compounds from lignocelluloses.

The chemical logic of enzymatic lignin degradation

Lignin is an aromatic heteropolymer, found in plant cell walls as 20-30% of lignocellulose. It represents the most abundant source of renewable aromatic carbon in the biosphere, hence, if it could be depolymerised efficiently, then it would be a highly valuable source of renewable aromatic chemicals. However, lignin presents a number of difficulties for biocatalytic or chemocatalytic breakdown. Research over the last 10 years has led to the identification of new bacterial enzymes for lignin degradation, and the use of metabolic engineering to generate useful bioproducts from microbial lignin degradation. The aim of this article is to discuss the chemical mechanisms used by lignin-degrading enzymes and microbes to break down lignin, and to describe current methods for generating aromatic bioproducts from lignin using enzymes and engineered microbes.

Unleashing the capacity of Rhodococcus for converting lignin into lipids

Bioconversion of bioresources/wastes (e.g., lignin, chemical pulping byproducts) represents a promising approach for developing a bioeconomy to help address growing energy and materials demands. Rhodococcus, a promising microbial strain, utilizes numerous carbon sources to produce lipids, which are precursors for synthesizing biodiesel and aviation fuels. However, compared to chemical conversion, bioconversion involves living cells, which is a more complex system that needs further understanding and upgrading. Various wastes amenable to bioconversion are reviewed herein to highlight the potential of Rhodococci for producing lipid-derived bioproducts. In light of the abundant availability of these substrates, Rhodococcus' metabolic pathways converting them to lipids are analyzed from a "beginning-to-end" view. Based on an in-depth understanding of microbial metabolic routes, genetic modifications of Rhodococcus by employing emerging tools (e.g., multiplex genome editing, biosensors, and genome-scale metabolic models) are presented for promoting the bioconversion. Co-solvent enhanced lignocellulose fractionation (CELF) strategy facilitates the generation of a lignin-derived aromatic stream suitable for the Rhodococcus' utilization. Novel alkali sterilization (AS) and elimination of thermal sterilization (ETS) approaches can significantly enhance the bioaccessibility of lignin and its derived aromatics in aqueous fermentation media, which promotes lipid titer significantly. In order to achieve value-added utilization of lignin, biodiesel and aviation fuel synthesis from lignin and lipids are further discussed. The possible directions for unleashing the capacity of Rhodococcus through synergistically modifying microbial strains, substrates, and fermentation processes are proposed toward a sustainable biological lignin valorization.

Recent Advances in Tailored Fabrication and Properties of Biobased Self-Healing Polyurethane

With the emergence of challenges in the environmental degradation and resource scarcity fields, the research of biobased self-healing polyurethane (BSPU) has become a prevailing trend in the technology of the polyurethane industry and a promising direction for developing biomass resources. Here, the production of BSPU from lignocellulose, vegetable oil, chitosan, collagen, and coumarin is classified, and the principles of designing polyurethane based on compelling examples using the latest methods and current research are summarized. Moreover, the impact of biomass materials on self-healing and mechanical properties, as well as the tailored performance method, are presented in detail. Finally, the applications of BSPU in biomedicine, sensors, coatings, etc. are also summarized, and the possible challenges and development prospects are explored to helpfully make progress in the development of BSPU. These findings demonstrate valuable references and practical significance for future BSPU research.

Structure and biochemical characterization of an extradiol 3,4-dihydroxyphenylacetate 2,3-dioxygenase from Acinetobacter baumannii

3,4-Dihydroxyphenylacetate (DHPA) 2,3-dioxygenase (EC 1.13.11.15) from Acinetobacter baumannii (AbDHPAO) is an enzyme that catalyzes the 2,3-extradiol ring-cleavage of DHPA in the p-hydroxyphenylacetate (HPA) degradation pathway. While the biochemical reactions of various DHPAOs have been reported, only structures of DHPAO from Brevibacterium fuscum and their homologs are available. Here, we report the X-ray structure and biochemical characterization of an Fe2+-specific AbDHPAO that shares 12% sequence identity to the enzyme from B. fuscum. The 1.8 Å X-ray structure of apo-AbDHPAO was determined with four subunits per asymmetric unit, consistent with a homotetrameric structure. Interestingly, the αβ-sandwiched fold of the AbDHPAO subunit is different from the dual β-barrel-like motif of the well-characterized B. fuscum DHPAO structures; instead, it is similar to the structures of non-DHPA extradiol dioxygenases from Comamonas sp. and Sphingomonas paucimobilis. Similarly, these extradiol dioxygenases share the same chemistry owing to a conserved 2-His-1-carboxylate catalytic motif. Structure analysis and molecular docking suggested that the Fe2+ cofactor and substrate binding sites consist of the conserved residues His12, His57, and Glu238 forming a 2-His-1-carboxylate motif ligating to Fe2+ and DHPA bound with Fe2+ in an octahedral coordination. In addition to DHPA, AbDHPAO can also use other 3,4-dihydroxyphenylacetate derivatives with different aliphatic carboxylic acid substituents as substrates, albeit with low reactivity. Altogether, this report provides a better understanding of the structure and biochemical properties of AbDHPAO and its homologs, which is advancing further modification of DHPAO in future applications.

Multi-stage nuclear transcriptomic insights of morphogenesis and biparental role changes in Lentinula edodes

Based on six offspring with different mitochondrial (M) and parental nuclear (N) genotypes, the multi-stage morphological characteristics and nuclear transcriptomes of Lentinula edodes were compared to investigate morphogenesis mechanisms during cultivation, the key reason for cultivar resistance to genotype changes, and regulation related to biparental role changes. Six offspring had specific transcriptomic data and morphological characteristics that were mainly regulated by the two parental nuclei, followed by the cytoplasm, at different growth stages. Importing a wild N genotype easily leads to failure or instability of fruiting; however, importing wild M genotypes may improve cultivars. Major facilitator superfamily (MFS) transporter genes encoding specific metabolites in spawns may play crucial roles in fruiting body formation. Pellets from submerged cultivation and spawns from sawdust substrate cultivation showed different carbon metabolic pathways, especially in secondary metabolism, degradation of lignin, cellulose and hemicellulose, and plasma membrane transport (mainly MFS). When the stage of small young pileus (SYP) was formed on the surface of the bag, the spawns inside were mainly involved in nutrient accumulation. Just broken pileus (JBP) showed a different expression of plasma membrane transporter genes related to intracellular material transport compared to SYP and showed different ribosomal proteins and cytochrome P450 functioning in protein biosynthesis and metabolism than near spreading pileus (NSP). Biparental roles mainly regulate offspring metabolism, growth, and morphogenesis by differentially expressing specific genes during different vegetative growth stages. Additionally, some genes encoding glycine-rich RNA-binding proteins, F-box, and folliculin-interacting protein repeat-containing proteins may be related to multi-stage morphogenesis. KEY POINTS: • Replacement of nuclear genotype is not suitable for cultivar breeding of L. edodes. • Some genes show a biparental role-divergent expression at mycelial growth stage. • Transcriptomic changes of some sawdust substrate cultivation stages have been elucidated.

Lignin to value-added products: Research updates and prospects

Due to the urgent need for renewable and clean energy, the efficient use of lignin is of wide interest. A comprehensive understanding of the mechanisms of lignin depolymerization and the generation of high-value products will contribute to the global control of the formation of efficient lignin utilization. This review explores the lignin value-adding process and discusses the link between lignin functional groups and value-added products. Mechanisms and characteristics of lignin depolymerization methods are presented, and challenges and prospects for future research are highlighted.

Prospects for utilizing microbial consortia for lignin conversion

Naturally occurring microbial communities are able to decompose lignocellulosic biomass through the concerted production of a myriad of enzymes that degrade its polymeric components and assimilate the resulting breakdown compounds by members of the community. This process includes the conversion of lignin, the most recalcitrant component of lignocellulosic biomass and historically the most difficult to valorize in the context of a biorefinery. Although several fundamental questions on microbial conversion of lignin remain unanswered, it is known that some fungi and bacteria produce enzymes to break, internalize, and assimilate lignin-derived molecules. The interest in developing efficient biological lignin conversion approaches has led to a better understanding of the types of enzymes and organisms that can act on different types of lignin structures, the depolymerized compounds that can be released, and the products that can be generated through microbial biosynthetic pathways. It has become clear that the discovery and implementation of native or engineered microbial consortia could be a powerful tool to facilitate conversion and valorization of this underutilized polymer. Here we review recent approaches that employ isolated or synthetic microbial communities for lignin conversion to bioproducts, including the development of methods for tracking and predicting the behavior of these consortia, the most significant challenges that have been identified, and the possibilities that remain to be explored in this field.

Integrative omics analyses of the ligninolytic Rhodosporidium fluviale LM-2 disclose catabolic pathways for biobased chemical production

BACKGROUND

Lignin is an attractive alternative for producing biobased chemicals. It is the second major component of the plant cell wall and is an abundant natural source of aromatic compounds. Lignin degradation using microbial oxidative enzymes that depolymerize lignin and catabolize aromatic compounds into central metabolic intermediates is a promising strategy for lignin valorization. However, the intrinsic heterogeneity and recalcitrance of lignin severely hinder its biocatalytic conversion. In this context, examining microbial degradation systems can provide a fundamental understanding of the pathways and enzymes that are useful for lignin conversion into biotechnologically relevant compounds.

RESULTS

Lignin-degrading catabolism of a novel Rhodosporidium fluviale strain LM-2 was characterized using multi-omic strategies. This strain was previously isolated from a ligninolytic microbial consortium and presents a set of enzymes related to lignin depolymerization and aromatic compound catabolism. Furthermore, two catabolic routes for producing 4-vinyl guaiacol and vanillin were identified in R. fluviale LM-2.

CONCLUSIONS

The multi-omic analysis of R. fluviale LM-2, the first for this species, elucidated a repertoire of genes, transcripts, and secreted proteins involved in lignin degradation. This study expands the understanding of ligninolytic metabolism in a non-conventional yeast, which has the potential for future genetic manipulation. Moreover, this work unveiled critical pathways and enzymes that can be exported to other systems, including model organisms, for lignin valorization.

Efficient Azo Dye Biodecolorization System Using Lignin-Co-Cultured White-Rot Fungus

The extensive use of azo dyes by the global textile industry induces significant environmental and human health hazards, which makes efficient remediation crucial but also challenging. Improving dye removal efficiency will benefit the development of bioremediation techniques for textile effluents. In this study, an efficient system for azo dye (Direct Red 5B, DR5B) biodecolorization is reported, which uses the white-rot fungus Ganoderma lucidum EN2 and alkali lignin. This study suggests that the decolorization of DR5B could be effectively enhanced (from 40.34% to 95.16%) within 48 h in the presence of alkali lignin. The dye adsorption test further confirmed that the alkali-lignin-enhanced decolorization of DR5B was essentially due to biodegradation rather than physical adsorption, evaluating the role of alkali lignin in the dye biodegradation system. Moreover, the gas chromatography/mass spectrometry analysis and DR5B decolorization experiments also indicated that alkali lignin carried an excellent potential for promoting dye decolorization and displayed a significant role in improving the activity of lignin-modifying enzymes. This was mainly because of the laccase-mediator system, which was established by the induced laccase activity and lignin-derived small aromatic compounds.

Efficient biosynthesis of pinosylvin from lignin-derived cinnamic acid by metabolic engineering of Escherichia coli

BACKGROUND

The conversion of lignin-derived aromatic monomers into valuable chemicals has promising potential to improve the economic competitiveness of biomass biorefineries. Pinosylvin is an attractive pharmaceutical with multiple promising biological activities.

RESULTS

Herein, Escherichia coli was engineered to convert the lignin-derived standard model monomer cinnamic acid into pinosylvin by introducing two novel enzymes from the wood plant: stilbene synthase from Pinus pinea (PpSTS) and 4-Coumarate-CoA ligase from Populus trichocarpa (Ptr4CL4). The expression of Ptr4CL4 drastically improved the production of pinosylvin (42.5 ± 1.1 mg/L), achieving values 15.7-fold higher than that of Ptr4CL5 (another 4-Coumarate-CoA ligase from Populus trichocarpa) in the absence of cerulenin. By adjusting the expression strategy, the optimized engineered strain produced pinosylvin at 153.7 ± 2.2 mg/L with an extremely high yield of 1.20 ± 0.02 mg/mg cinnamic acid in the presence of cerulenin, which is 83.9% ± 1.17 of the theoretical yield. This is the highest reported pinosylvin yield directly from cinnamic acid to date.

CONCLUSION

Our work highlights the feasibility of microbial production of pinosylvin from cinnamic acid and paves the way for converting lignin-related aromatics to valuable chemicals.

Creative biological lignin conversion routes toward lignin valorization

Lignin, the largest renewable aromatic resource, is a promising alternative feedstock for the sustainable production of various chemicals, fuels, and materials. Despite this potential, lignin is characterized by heterogeneous and macromolecular structures that must be addressed. In this review, we present biological lignin conversion routes (BLCRs) that offer opportunities for overcoming these challenges, making lignin valorization feasible. Funneling heterogeneous aromatics via a 'biological funnel' offers a high-specificity bioconversion route for aromatic platform chemicals. The inherent aromaticity of lignin drives atom-economic functionalization routes toward aromatic natural product generation. By harnessing the ligninolytic capacities of specific microbial systems, powerful aromatic ring-opening routes can be developed to generate various value-added products. Thus, BLCRs hold the promise to make lignin valorization feasible and enable a lignocellulose-based bioeconomy.

Efficient O-demethylation of lignin monoaromatics using the peroxygenase activity of cytochrome P450 enzymes

Selective O-demethylation of the lignin monoaromatics, syringol and guaiacol, using the peroxygenase activity of two distinct cytochrome P450 enzymes.