Engineered Microbial Cellulases for Biomass Conversion: Integrating Omics, Expression Platforms, Fermentation Engineering and Enzyme Reusability.

Lignocellulolytic enzymes in circular biorefineries: Challenges, barriers, and integrative solutions for next generation bioeconomy.

The sustainable bioeconomy fundamentally relies on the effective valorization of lignocellulosic biomass into renewable fuels and high-value biochemicals. Although extensive research has been conducted over several decades, commercialization remains hindered by enzyme instability, low catalytic efficiency, high production costs, and the intrinsic recalcitrance of biomass. While previous reviews have separately discussed lignocellulolytic enzymes, biomass conversion, or circular bioeconomy strategies, comprehensive integration of recent molecular, microbial, and process-engineering advancements remains limited. Therefore, this review provides a multidisciplinary perspective integrating enzyme engineering, microbial co-culturing, heterologous gene expression, advanced biomass pretreatment, and bioprocess optimization within a unified biorefinery framework. The review critically links molecular-level improvements, including protein engineering, codon optimization, and thermostability enhancement, with industrial process strategies such as consolidated bioprocessing, consolidated bio-saccharification, and techno-economic optimization. Emerging approaches including CRISPR/Cas9-mediated strain improvement, artificial cellulosomes, nanobiotechnology, and AI-assisted modeling are discussed as supportive tools for improving biomass conversion efficiency and industrial applicability. In addition, major bottlenecks such as enzyme instability, biomass recalcitrance, and process incompatibilities are critically evaluated along with recent strategies to overcome these limitations. By integrating molecular biology, microbial engineering, and process-level innovations, this review provides a comprehensive framework for the development of sustainable and scalable lignocellulosic biorefineries supporting the circular bioeconomy.

Production of Cellulases by Trichoderma, Aspergillus, and Penicillium: Optimization Strategies, Biomass Valorization, and Industrial Perspectives

Fungal cellulases are key biocatalysts for lignocellulosic biomass valorization and the development of sustainable biorefineries and the complementary characteristics of these fungi genera support their application in integrated biomass conversion and future lignocellulosic biorefineries.

Cyanobacterial biorefinery: sustainable wastewater management for generation of biofuels and high-value products aligning with a circular economy approach

Xylitol Biomanufacturing: Production Technologies, Industrial Applications and Future Opportunities

Xylitol is a five-carbon sugar alcohol widely used in the food, pharmaceutical, oral healthcare, and personal care industries because of its low caloric value, low glycaemic index, and non-cariogenic properties. Industrial production is mainly based on catalytic hydrogenation of xylose, which provides high conversion efficiency but requires intensive energy input, costly catalysts, and complex purification processes. Microbial fermentation has emerged as a sustainable alternative for producing xylitol from renewable lignocellulosic biomass. This review summarizes recent advances in xylitol production, with a particular focus on microbial biomanufacturing. Key developments in lignocellulosic biomass utilization, metabolic engineering, cofactor balancing, oxygen regulation, and fermentation optimization are discussed. Chemical and biological production routes are critically compared in terms of efficiency, sustainability, and industrial applicability. Recent progress in downstream purification and biorefinery integration is also highlighted. Despite substantial advances, challenges including inhibitor toxicity, limited microbial robustness, low fermentation productivity, and high purification costs continue to hinder large-scale commercialization. Future research should focus on feedstock valorization, systems metabolic engineering, process intensification, and sustainable separation technologies to improve the economic and environmental sustainability of bio-based xylitol production.

Bioprocess Engineering for Enzyme Manufacturing: A Systems Approach to Production, Purification, and Formulation

Enzymes constitute one of the largest and fastest-growing sectors of industrial biotechnology, serving as environmentally sustainable biocatalysts in food and beverage processing, fermentation industries, biofuel production, detergents, textiles, leather processing, pulp and paper manufacturing, pharmaceuticals, nutraceuticals, animal feed, and environmental remediation. Their exceptional catalytic efficiency, substrate specificity, and ability to operate under mild reaction conditions have enabled the replacement of numerous conventional chemical catalysts, thereby reducing energy consumption, hazardous waste generation, and overall environmental impact. Continuous advances in microbial biotechnology, metabolic engineering, protein engineering, synthetic biology, and precision fermentation have significantly improved enzyme productivity, catalytic performance, process economics, and industrial scalability. This review comprehensively examines four interconnected pillars of industrial enzyme biotechnology: (i) microbial fermentation technologies, (ii) downstream processing and industrial scale-up, (iii) bioprocess optimization, and (iv) enzyme formulation and delivery systems. Current fermentation strategies—including submerged fermentation (SmF), solid-state fermentation (SSF), batch, fed-batch, and continuous cultivation—are critically evaluated with respect to productivity, substrate utilization, scalability, and commercial feasibility. Recent advances in downstream processing, encompassing biomass separation, enzyme concentration, purification, stabilization, drying, and quality assurance, are discussed with emphasis on maximizing product recovery while minimizing activity loss and manufacturing costs. Modern bioprocess optimization approaches—including Design of Experiments (DoE), Response Surface Methodology (RSM), systems biology, metabolic engineering, artificial intelligence-assisted process control, digital bioprocessing, and Process Analytical Technology (PAT)—are highlighted for their roles in improving enzyme yield, productivity, robustness, and manufacturing efficiency. Furthermore, recent developments in enzyme formulation technologies, including liquid concentrates, powder formulations, immobilized enzymes, nanoformulations, encapsulation, and controlled-release delivery systems, are reviewed for their ability to enhance enzyme stability, shelf life, transportability, and industrial performance. By integrating upstream production, downstream recovery, process optimization, and formulation technologies into a unified framework, this review provides a holistic perspective on industrial enzyme manufacturing. The article serves as a comprehensive resource for researchers, industrial microbiologists, biochemical engineers, and biotechnology professionals seeking to develop economically viable, sustainable, and high-performance enzyme production systems. Future progress is expected to arise from the convergence of synthetic biology, machine learning, precision fermentation, digital bioprocessing, and circular bioeconomy concepts, thereby enabling next-generation sustainable enzyme manufacturing.

Myceliophthora thermophila as a Biotechnological Platform for Cellulase Production and Lignocellulose Valorization

Lignocellulosic biomass deconstruction requires robust biocatalysts capable of operating under demanding industrial conditions. The thermophilic fungus Myceliophthorathermophila is a promising biotechnological platform for cellulase production and lignocellulose valorization because of its naturally thermostable CAZyme repertoire. Extensive knowledge has accumulated across diverse research fields, alongside its taxonomic reclassification as Thermothelomyces thermophila, emphasizing the need to integrate findings across research contexts. This review synthesizes knowledge generated using publicly available M. thermophila strains, retaining the historically prevalent name M. thermophila to facilitate cross-disciplinary comparison. Emphasis is placed on the C1 strain, whose longstanding use as a production platform provides a foundation for current advances in strain engineering and protein production. We provide a genetics-focused perspective on this biotechnological platform, integrating advances in genetic engineering, transcriptional regulation, and protein production. We discuss CRISPR systems applied to M. thermophila, strategies to improve protein production through extracellular protease elimination, optimization of secretion and unfolded protein response pathways, carrier proteins, and synthetic expression systems. We further summarize the transcriptional regulation of cellulase expression, the repertoire of characterized thermostable cellulases, and opportunities for protein engineering. Collectively, these advances position M. thermophila as a versatile biotechnological platform for producing industrial enzymes and other value-added bioproducts for biorefinery applications.