Lignin valorization using biological approach

Abstract

Due to the structural complexity and recalcitrance nature of lignin, its depolymerization into monomeric units becomes one of the biggest challenges in the bioconversion of lignin into value-added products. Depolymerization of lignin produces a blend of many compounds that are problematic for isolating components in a cost-effective way. Lignin valorization using a biological approach facilitates sustainable and commercially viable biorefineries. The use of microbes for the conversion of depolymerized lignin compounds into target products can be a solution to the heterogeneity issue. Several studies have been carried out to develop robust strains that can utilize all relevant lignin-derived compounds, but constructing these strains is difficult. As an alternative, designing multiple microbes to convert a mixture of various compounds into the desired product seems realistic. This review provides an overview of lignin bioconversion using various approaches such as metabolic engineering and synthetic biology. Ligninolytic strains have a broad enzymatic machine for depolymerization of lignin and its conversion into intermediates such as catechol or protocatechuate. These intermediates can be further converted to metabolite products such as polyhydroxyalkanoates and triacylglycerol. Synthetic biology offers encouraging methodologies to construct pathways for lignin conversion and to engineer ligninolytic microbes as prospective strains for lignin bioconversion. ©

Multi‐Enzymatic Cascade Reactions for the Synthesis of cis,cis‐Muconic Acid

“…[1,5] Nevertheless, lignin valorisation is feasible by performing its thermochemical or biological depolymerisation into monomeric aromatic compounds. [1,[6][7][8][9] These compounds represent building blocks for the sustainable synthesis of chemicals, such as adipic acid, cis,cis-muconic acid ((2Z,4Z)-hexa-2,4-dienedioic acid, ccMA) and terephthalic acid. [1,10] Because of the relevance of these compounds as precursors of commercial plastics, biological routes for their production have been already implemented and scaled up to the pilot scale, representing the masterpiece of lignin valorization.…”

“…In fact, as its calorific power is comparable to that of some fossil carbons (26–28 MJ/ton dry lignin), approximately 140 million tons per year of technical lignin is burned for the in loco generation of heat and power [1,5] . Nevertheless, lignin valorisation is feasible by performing its thermochemical or biological depolymerisation into monomeric aromatic compounds [1,6–9] . These compounds represent building blocks for the sustainable synthesis of chemicals, such as adipic acid, cis,cis ‐muconic acid ((2Z,4Z)‐hexa‐2,4‐dienedioic acid, ccMA) and terephthalic acid [1,10] .…”

Sustainable lignin modifications and processing methods: green chemistry as the way forward

“…- Lack of understanding of (1) the possible synergetic effect between different enzymes, (2) the beneficial or disadvantageous effect of different mediators and (3) the enzyme-mediator systems. 196,211…”

Transformation of Corn Stover into Furan Aldehydes by One-Pot Reaction with Acidic Lithium Bromide Solution

“…Cellulose, hemicellulose, and lignin are the main components of lignocellulose. Xylan is the main component of hemicellulose, which is easily degraded during moderate-severity acidic treatment [ 5 , 6 ]. Currently, the industrial furfural production process is based on a H 2 SO 4 -catalyzed reaction at temperatures ranging from 153 °C to 240 °C.…”

“…During the reaction, the hemicellulose was first degraded to pentose. Then, pentose was further dehydrated into furfural [ 6 , 7 ]. The theoretical yield of pentose to furfural is 0.73 kg/kg pentose [ 8 ]; however, the yield of furfural in industrial practice is only about 50–55% of the theoretical yield [ 4 , 9 , 10 , 11 ].…”