About this Research Topic
The key aim of biorefineries is to offer a sustainable, renewable, and commercially feasible alternative to the drawbacks of fossil fuel-based products by ensuring optimized utilization of plant biomass residues. This approach relies on the rational conversion of plant polymers into commercially relevant products such as biofuels, commodity chemicals, food ingredients and pharmaceuticals. However, to allow the effective synthesis of such products, the polymers of the plant biomass first have to be efficiently degraded into monomeric elements that can serve as starting materials, or building blocks, for the production of high added-value compounds. This step depends on cocktails of carbohydrate-active enzymes (CAZymes).
The degradation of cellulose to glucose typically requires the combined activity of endoglucanases, lytic polysaccharide monooxygenases (LPMOs), cellobiohydrolases and β-glucosidases, while hydrolyses of hemicellulose requires endoxylanases, β-xylosidases and accessory enzymes forming products like xylose, mannose, arabinose and ferulic acid. Conversely, lignin is degraded by different oxidases and peroxidases. The used cocktails of recombinant CAZymes are typically produced using filamentous fungi, mainly Aspergillus spp. and Trichoderma reesei, due to their efficient endogenous enzyme secretion pathways.
Although enzymatic degradation of plant biomass is well-established, due to the costs involved in the process, it is evident that more efficient enzyme production methods, as well as more efficient CAZymes and cocktails, need to be developed. For these purposes, several approaches can be applied to overcome bottlenecks and drawbacks that still limit CAZyme utilization: new strategies and tools, including “omics” approaches applied to gene prospection for the selection of highly active and stable CAZymes; design of CAZymes with improved characteristics by rational protein engineering; rational genetic engineering, or adaptive evolution of microbial strains to improve CAZyme production; introduction of biosynthetic enzymes to produce high added-value compounds from plant biomass substrates during hydrolysis. We would like to invite authors to contribute high-quality original research, as well as review articles, covering different aspects of enzyme-based hydrolysis of plant biomass in the context of optimizing biorefinery process, as well as the following areas:
• “Omics” based approaches aimed at prospection for improved CAZymes:
- Metagenome, metatranscriptome, and metaproteome based approaches
- Bioinformatics tools aimed at CAZyme bioprospecting
• CAZyme engineering for improvement of enzyme properties:
- Directed evolution of proteins
- Rational design of proteins
• Microbial strain engineering:
- Filamentous fungi, yeast and bacteria as protein/enzyme cell factories
- Engineering of gene expression and regulation related to CAZyme production
- System for homologous and/or heterologous expression in relevant organism
- Use of CRISPR/Cas9 for the construction of improved strains
• CAZyme application in biorefinery:
- Novel CAZyme cocktails for plant biomass deconstruction
- Use of biosynthetic enzymes to form new added-value products in biorefineries
Keywords: CAZymes, Biorefinery, Enzyme Engineering, Cell Factories, Omics Approaches
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