Synthetic Biology towards Engineering Microbial Lignin Biotransformation

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

“…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] .…”

“…The DH1 strain of Escherichia coli was engineered with a new anabolic pathway for the bioconversion of vanillin (obtained from the thermochemical pre‐treatment of lignin) into ccMA (314 mg ccMA/L culture; 0.69 g ccMA/g vanillin) [10] . Nonetheless, the limits of this approach consist both in the difficulty of the microbial pathway regulation (i. e. strain engineering) and in the set up of the optimal microbial growth conditions [7,13] . To overcome these limitations, multi‐enzymatic biocatalytic approaches could represent a suitable strategy: [14–16] system biocatalysis allows the combination of different enzymes, also from different source organisms, in a single reactor resulting in the generation of new routes for the product synthesis [15,17,18] .…”

“…[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.…”

“…[10] Nonetheless, the limits of this approach consist both in the difficulty of the microbial pathway regulation (i. e. strain engineering) and in the set up of the optimal microbial growth conditions. [7,13] To overcome these limitations, multi-enzymatic biocatalytic approaches could represent a suitable strategy: [14][15][16] system biocatalysis allows the combination of different enzymes, also from different source organisms, in a single reactor resulting in the generation of new routes for the product synthesis. [15,17,18] Cascade reactions are advantageous over classical step-by-step synthesis since these allow the elimination of the steps for isolation and purification of reaction intermediates, the handling of unstable intermediates, higher yields (by shifting of unfavourable reaction equilibria), and improved atom economy.…”

Lignin to value-added chemicals and advanced materials: extraction, degradation, and functionalization

“…121 For example, white rot fungi can produce laccase, LiP, and MnP to deconstruct lignin into CO 2 and H 2 O. 122…”