Lignin Biodegradation and Its Valorization

Abstract

Lignin, a rigid polymer composed of phenolic subunits with high molecular weight and complex structure, ranks behind only cellulose in the contribution to the biomass of plants. Therefore, lignin can be used as a new environmentally friendly resource for the industrial production of a variety of polymers, dyes and adhesives. Since laccase was found to be able to degrade lignin, increasing attention had been paid to the valorization of lignin. Research has mainly focused on the identification of lignin-degrading enzymes, which play a key role in lignin biodegradation, and the potential application of lignin degradation products. In this review, we describe the source, catalytic specificity and enzyme reaction mechanism of the four classes of the lignin-degrading enzymes so far discovered. In addition, the major pathways of lignin biodegradation and the applications of the degradative products are also discussed. Lignin-degrading bacteria or enzymes can be used in combination with chemical pretreatment for the production of value-added chemicals from lignin, providing a promising strategy for lignin valorization.

Description of Dissolved Organic Matter Transformational Networks at the Molecular Level

“…Although the molecular transformations resulting from CID fragmentation may be different than the ones triggered by enzymatically driven microbial processing, several studies have shown some interesting similarities in their pathways. For example, decarboxylation (CO 2 neutral loss during CID) has been recognized as a biodegradation mechanism of tannins and a fundamental reaction pathway of DOM photooxidation. , Moreover, demethoxylation pathways, correlated with CH 4 O neutral losses, have been previously reported during degradation of lignin, a potential DOM component. − The absence of methoxy (CH 4 O loss)-based transformational processes in the common CHO structural families suggests that the mechanisms triggering the addition/subtraction of this functionality are characteristic to certain aquatic ecosystems. Examination of the neutral loss sequences among precursors in the families (data not shown) evidenced that at least one methoxy moiety was found in ∼50% of both SRFA and Pantanal structural families.…”

“…In contrast, lower abundance of this functionality was observed across HR-1 (<7%) and HR-5 (<3%) structural families, thus confirming the similarities between SRFA/Pantanal and HR-1/HR-5 pairs at the structural level. Interestingly, the replacement of methoxy functional groups with phenolic hydroxyl groups has been previously linked to biodegradation of highly methoxylated lignin. − Therefore, transformation mechanisms involving methoxy moieties may be constrained in estuarine systems (HR-1/HR-5) due to extensive upstream lignin biodegradation.…”

Opportunities and Challenges for Lignin Valorization in Food Packaging, Antimicrobial, and Agricultural Applications

“…The American Society for Testing and Materials (ASTM) defines a plastic as compostable when it “undergoes degradation by biological processes during composting to yield carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known compostable materials and that leaves no visible, distinguishable, or toxic residue.” This is a subgroup of biodegradable plastics, which are instead defined as “plastic in which the degradation results from the action of naturally-occurring micro-organisms such as bacteria, fungi, and algae.” Therefore, not all biodegradable plastics are compostable. Lignin is efficiently biodegraded by white-rot fungi and various types of bacteria, , but the degradation of lignin under composting conditions commonly used to dispose of food packaging items is incomplete and inefficient . Moreover, the properties introduced by the addition of lignin in a polymer matrix, such as improved gas barrier, decreased water permeability, and increased hydrophobicity, can reduce the material degradability in the composting conditions.…”

Valorization of Lignocellulosic Biomass into Biofuels and Value-Added Products for Sustainable Environment: A Comprehensive Review

“…Lignin, an aromatic polymer of LCB acts as a physical barrier in the process of polysaccharides extraction [1, 3,14]. It is degraded by a variety of ligninolytic enzymes such as laccases, versatile peroxidase manganese peroxidase, and lignin peroxidase [100]. Microorganisms (fungi and bacteria) are commonly used for the production of hydrolytic enzymes.…”

“…Microorganisms (fungi and bacteria) are commonly used for the production of hydrolytic enzymes. Micro-organisms such as Bacillus velezensis, Bacillus paranthracis, Aspergillus terreus, Aspergillus niger, Trametes versicolor, and Phanerochaete chrysosporium are few of the examples which produce enzymes with cellulolytic, hemicellulolytic, and ligninolytic capabilities [2,100]. Various factors such as enzymatic activity of saccharification enzymes, enzyme loading, substrate quantity, process conditions, and inhibitors present in the postpretreatment sugar hydrolysate [89].…”