Recent advances in lignin valorization with bacterial cultures: microorganisms, metabolic pathways, and bio-products

Abstract

Lignin is the most abundant aromatic substrate on Earth and its valorization technologies are still under developed. Depolymerization and fragmentation are the predominant preparatory strategies for valorization of lignin to chemicals and fuels. However, due to the structural heterogeneity of lignin, depolymerization and fragmentation typically result in diverse product species, which require extensive separation and purification procedures to obtain target products. For lignin valorization, bacterial-based systems have attracted increasing attention because of their diverse metabolisms, which can be used to funnel multiple lignin-based compounds into specific target products. Here, recent advances in lignin valorization using bacteria are critically reviewed, including lignin-degrading bacteria that are able to degrade lignin and use lignin-associated aromatics, various associated metabolic pathways, and application of bacterial cultures for lignin valorization. This review will provide insight into the recent breakthroughs and future trends of lignin valorization based on bacterial systems.

Why Does Phlebiopsis gigantea not Always Inhibit Root and Butt Rot in Conifers?

“…Peroxidase production was not correlated with cellulase production, but was strongly correlated with the presence of vanillic and protocatechuic acid. Xu et al [77] describe pathways of enzymatic degradation of lignin, where protocatechuic and vanillic acids are key byproducts of decay.Żółciak et al [26] also found that the concentration of protocatechuic acid was many times greater than that of vanillic acid. Protocatechuic acid is the common byproduct of two pathways of lignin degradation, namely G-lignin and H-lignin decay, whereas vanillic acid appears only during G-lignin decomposition.…”

Narrative of a versatile and adept species Pseudomonas putida

“…P. putida is also a promising alternative platform for production of rhamnolipids, biodegradable bacterial biosurfactants, after introducing two genes of the rhamnolipid synthesis pathway from P. aeruginosa [127,128], and for the production of isoprenoids (terpenoids) with a diverse range of applications in areas such as the pharmaceutical industry [129]. In addition, lignocellulosic biomass from catalytic pyrolysis containing aromatic compounds could be converted by P. putida capable of utilizing such substrates into added-value products such as cis-cis muconate [125,130,131]. A good example of lignin valorization is the metabolically engineered P. putida KT2440 derivative with enhanced catechol tolerance and enhanced substrate spectrum that was employed to the conversion of hydrothermally depolymerized softwood lignin to nylon [132].…”

Biotransformation of lignin: Mechanisms, applications and future work

“…81 Depending on specific structure of lignin monomers and specific environmental conditions, the funneling process may take several steps with the involvement of diverse enzymes, such as acryl-CoA synthetase, acryl-CoA hydratase, dehydrogenase, decarboxylases, and O-demethylase system. 85 Among the three categories of lignin monomers, H-type compounds (e.g., 4-coumarate) are ultimately converted into 4-hydroxybenzoate, while different pathways such as the CoA-dependent β-oxidation pathway, the CoA-dependent non-β-oxidation pathway, and the CoA-independent pathway have been identified. 84 and Sphingomonas paucimobilis.…”

“…84 and Sphingomonas paucimobilis. 85 Among the three categories of lignin monomers, H-type compounds (e.g., 4-coumarate) are ultimately converted into 4-hydroxybenzoate, while different pathways such as the CoA-dependent β-oxidation pathway, the CoA-dependent non-β-oxidation pathway, and the CoA-independent pathway have been identified. 83 The generated 4-hydroxybenzoate is then hydroxylated to protocatechuate via 4-hydroxybenzoate-3-hydroxylase ( Figure 3a).…”