Bioprospecting lignin for biorefinery: Emerging innovations and strategies in microbial technology

Developing biorefineries derived from plant biomass can help combat global warming by creating sustainable alternatives to depleting fossil-based products. Lignocellulosic biomass is a promising feedstock for biorefineries as it consists of cellulose, hemicellulose and lignin, which are efficiently converted into various valuable products such as biofuels, chemicals and other compounds through sustainable integrated biorefinery processes. While cellulose and hemicellulose contribute to glucose and various types of fermentable sugars for the production of valuable materials, lignin, with its aromatic structure and unique chemical properties, such as high carbonoxygen ratio, is very valuable in biorefinery processes. However, the resilience of lignin and its toxic effect on enzymatic reactions pose a major challenge to the commercial viability of current biorefineries, which require advanced technologies to enable effective lignin degradation and to valorize and utilize the lignin. Although physical and chemical approaches have been explored, a sustainable approach is the enzymatic degradation of lignin by microbes. Bioprospecting of microorganisms using culture-dependent and culture-independent techniques to identify novel microbes, genes and enzymes mediating lignin depolymerization and their characterization is employed. Further improvements can be achieved with biotechnological methods such as protein and genetic engineering. Protein engineering uses directed evolution and rational design, while genetic engineering methods include heterologous/homologous gene expression and CRISPR/Cas9-based gene editing. Systems biology can better understand the complex interaction between microbes, their enzymes and lignin. These approaches contribute to advancing the valorization of lignin in biorefineries, and policy changes in favor of integrating this technology into society are critical to its success.