Extreme Glycosyl Hydrolases: strategic biological agents for the circular economy

Glycosyl hydrolases (GH) are enzymes that catalyze the hydrolysis of glycosidic bonds in complex polysaccharides, such as cellulose and starch, and are among the most important biocatalysts applied in biorefinery processes. Significant amounts of carbohydrate-rich substrates are present in agro-industrial by-products and effluents, making the efficient conversion of these materials a strategic challenge. In this context, the investigation of GHs capable of withstanding extreme conditions of temperature, pH, and salinity commonly encountered during the bioprocessing of solid and liquid agricultural residues is of growing interest for the advancement of the circular economy. This review aims to explore extreme glycosyl hydrolases, with a particular emphasis on state-of-the-art enzymes, while also examining the global market and research and development opportunities through patent analysis and scientific literature published over the last decade. Microalgae and extremophilic microorganisms were identified as underexplored yet highly promising sources of GHs with unique catalytic properties. Finally, this study discusses the potential applications of GH-derived extremozymes in the development of innovative technologies aligned with circular economy principles. However, this review is limited to microbial glycosyl hydrolases with biotechnological potential, and does not include enzymes of plant or animal origin.