Anaerobic digestion using lignocellulosic material as the substrate is a cost-effective strategy for biomethane production, which provides great potential to convert biomass into renewable energy. However, the recalcitrance of native lignocellulosic biomass makes it resistant to microbial hydrolysis, which reduces the bioconversion efficiency of organic matter into biogas. Therefore, it is necessary to critically investigate the correlation between lignocellulose characteristics and bioconversion efficiency. Accordingly, this review comprehensively summarizes the anaerobic digestion process and rate-limiting step, structural and compositional properties of lignocellulosic biomass, recalcitrance and inhibitors of lignocellulose and their major effects on anaerobic digestion for biomethane production. Moreover, various type of pretreatment strategies applied to lignocellulosic biomass was discussed in detail, which would contribution to cell wall degradation and improvement of biomethane yields. In the view of current knowledge, high energy input and cost requirements are the main limitations of these pretreatment methods. In addition to optimization of fermentation process, further studies should focus much more on key structural influence factors of biomass recalcitrance and anaerobic digestion efficiency, which will contribute to improvement of biomethane production from lignocellulose.

Thermophilic polyester hydrolases (PES-H) have recently enabled biocatalytic recycling of the mass-produced synthetic polyester polyethylene terephthalate (PET), which has found widespread use in the packaging and textile industries. The growing demand for efficient PET hydrolases prompted us to solve high-resolution crystal structures of two metagenome-derived enzymes (PES-H1 and PES-H2) and notably also in complex with various PET substrate analogues. Structural analyses and computational modeling using molecular dynamics simulations provided an understanding of how product inhibition and multiple substrate binding modes influence key mechanistic steps of enzymatic PET hydrolysis. Key residues involved in substrate-binding and those identified previously as mutational hotspots in homologous enzymes were subjected to mutagenesis. At 72 °C, the L92F/Q94Y variant of PES-H1 exhibited 2.3-fold and 3.4-fold improved hydrolytic activity against amorphous PET films and pretreated real-world PET waste, respectively. The R204C/S250C variant of PES-H1 had a 6.4 °C higher melting temperature than the wild-type enzyme but retained similar hydrolytic activity. Under optimal reaction conditions, the L92F/Q94Y variant of PES-H1 hydrolyzed low-crystallinity PET materials 2.2-fold more efficiently than LCC ICCG, which was previously the most active PET hydrolase reported in the literature. This property makes the L92F/Q94Y variant of PES-H1 a good candidate for future applications in industrial plastic recycling processes.

Plastic wastes, widely distributed in the environment, can be transformed into microplastics, posing a huge threat to ecosystems and human health due to their stability and adsorbability to other toxic pollutants (e.g., heavy metals and antibiotics). Recently, microbial degradation of (micro)plastics has gained widespread attention because of its green and sustainable properties. Microbial degradation of (micro)plastics is based on the cascade effects of various enzymes secreted by microorganisms, which can convert (micro)plastics into oligomers and monomers, or even mineralize them into CO₂ and H₂O. The microbial degradation of (micro)plastics is affected by multiple factors, such as microbial species, plastic properties, and environmental conditions. Currently, limited efficient plastic-degrading microorganisms have been discovered, and their degradation mechanisms are still unclear. Furthermore, the efficiency of microbial degradation needs to be improved for future application. Therefore, this review systematically summarizes the sources and properties of existing plastics, identifies pure cultures and mixed cultures for plastic degradation, and examines their influencing factors. In particular, the microbial degradation behaviors of (micro)plastics, including relevant enzymes, degradation efficiency, and degradation mechanisms, were thoroughly discussed. Additionally, the augmentation technologies coupling with microbial degradation, such as advanced oxidation, electrochemical, and genetic engineering technologies, were introduced and highlighted for their potential prospects. This review provides a reference for future research and development of (micro)plastic biodegradation technology.

Methanol has become an attractive substrate for biotechnological applications due to its abundance and low-price. Chemicals production from methanol could alleviate the environmental concerns, costs, and foreign dependency associated with the use of petroleum feedstock. Recently, a growing fraction of research has focused on metabolites production using methanol as sole carbon and energy source or as co-substrate with carbohydrates by native or synthetic methylotrophs. In this review, we summarized the recent significant progress in native and synthetic methylotrophs and their application for methanol bioconversion into various products. Moreover, strategies for improvement of methanol metabolism and new perspectives on the generation of desired products from methanol were also discussed, which will benefit for the development of a methanol-based economy.