Consolidated bio-saccharification: Leading lignocellulose bioconversion into the real world

A fragment of the β-glucosidase gene from the rumen fungus Neocallimastix patriciarum J11 encodes a recombinant protein that exhibits activities in β-glucosidase and β-glucanase

Lignocellulose, the most abundant organic waste on Earth, is of economic value because it can be converted into biofuels like ethanol by enzymes such as β-glucosidase. This study involved cloning a β-glucosidase gene named JBG from the rumen fungus Neocallimastix patriciarum J11. When expressed recombinantly in Escherichia coli, the rJBG enzyme exhibited significant activity, hydrolyzing 4-nitrophenyl-β-d-glucopyranoside and cellobiose to release glucose. Surprisingly, the rJBG enzyme also showed hydrolytic activity against β-glucan, breaking it down into glucose, indicating that the rJBG enzyme possesses both β-glucosidase and β-glucanase activities, a characteristic rarely found in β-glucosidases. When the JBG gene was expressed in Saccharomyces cerevisiae and the transformants were inoculated into a medium containing β-glucan as the sole carbon source, the ethanol concentration in the culture medium increased from 0.17 g/L on the first day to 0.77 g/L on the third day, reaching 1.3 g/L on the fifth day, whereas no ethanol was detected in the yeast transformants containing the recombinant plasmid pYES-Sur under the same conditions. These results demonstrate that yeast transformants carrying the JBG gene can directly saccharify β-glucan and ferment it to produce ethanol. This gene, with its dual β-glucosidase and β-glucanase activities, simplifies and reduces the cost of the typical process of converting lignocellulose into bioethanol using enzymes and yeast.

Powerful cell wall biomass degradation enzymatic system from saprotrophic Aspergillus fumigatus

Cell wall biomass, Earth's most abundant natural resource, holds significant potential for sustainable biofuel production. Composed of cellulose, hemicellulose, lignin, pectin, and other polymers, the plant cell wall provides essential structural support to diverse organisms in nature. In contrast, non-plant species like insects, crustaceans, and fungi rely on chitin as their primary structural polysaccharide. The saprophytic fungus Aspergillus fumigatus has been widely recognized for its adaptability to various environmental conditions. It achieves this by secreting different cell wall biomass degradation enzymes to obtain essential nutrients. This review compiles a comprehensive collection of cell wall degradation enzymes derived from A. fumigatus, including cellulases, hemicellulases, various chitin degradation enzymes, and other polymer degradation enzymes. Notably, these enzymes exhibit biochemical characteristics such as temperature tolerance or acid adaptability, indicating their potential applications across a spectrum of industries.

Composition of Lignocellulose Hydrolysate in Different Biorefinery Strategies: Nutrients and Inhibitors

The hydrolysis and biotransformation of lignocellulose, i.e., biorefinery, can provide human beings with biofuels, bio-based chemicals, and materials, and is an important technology to solve the fossil energy crisis and promote global sustainable development. Biorefinery involves steps such as pretreatment, saccharification, and fermentation, and researchers have developed a variety of biorefinery strategies to optimize the process and reduce process costs in recent years. Lignocellulosic hydrolysates are platforms that connect the saccharification process and downstream fermentation. The hydrolysate composition is closely related to biomass raw materials, the pretreatment process, and the choice of biorefining strategies, and provides not only nutrients but also possible inhibitors for downstream fermentation. In this review, we summarized the effects of each stage of lignocellulosic biorefinery on nutrients and possible inhibitors, analyzed the huge differences in nutrient retention and inhibitor generation among various biorefinery strategies, and emphasized that all steps in lignocellulose biorefinery need to be considered comprehensively to achieve maximum nutrient retention and optimal control of inhibitors at low cost, to provide a reference for the development of biomass energy and chemicals.

A cellulosomal double-dockerin module from Clostridium thermocellum shows distinct structural and cohesin-binding features

Cellulosomes are intricate cellulose-degrading multi-enzymatic complexes produced by anaerobic bacteria, which are valuable for bioenergy development and biotechnology. Cellulosome assembly relies on the selective interaction between cohesin modules in structural scaffolding proteins (scaffoldins) and dockerin modules in enzymes. Although the number of tandem cohesins in the scaffoldins is believed to determine the complexity of the cellulosomes, tandem dockerins also exist, albeit very rare, in some cellulosomal components whose assembly and functional roles are currently unclear. In this study, we characterized the structure and mode of assembly of a tandem bimodular double-dockerin, which is connected to a putative S8 protease in the cellulosome-producing bacterium, Clostridium thermocellum. Crystal and NMR structures of the double-dockerin revealed two typical type I dockerin folds with significant interactions between them. Interaction analysis by isothermal titration calorimetry and NMR titration experiments revealed that the double-dockerin displays a preference for binding to the cell-wall anchoring scaffoldin ScaD through the first dockerin with a canonical dual-binding mode, while the second dockerin module was unable to bind to any of the tested cohesins. Surprisingly, the double-dockerin showed a much higher affinity to a cohesin from the CipC scaffoldin of Clostridium cellulolyticum than to the resident cohesins from C. thermocellum. These results contribute valuable insights into the structure and assembly of the double-dockerin module, and provide the basis for further functional studies on multiple-dockerin modules and cellulosomal proteases, thus highlighting the complexity and diversity of cellulosomal components.

A natural consortium of thermophilic bacteria from Huancarhuaz hot spring (Ancash-Peru) for promising lignocellulose bioconversion

The lignocellulose bioconversion process is an eco-friendly and green-economy alternative technology that allows the reduction of pollution and global warming, so it is necessary for thermophilic and thermostable hydrolytic enzymes from natural sources. This research aimed to isolate cellulolytic and xylanolytic microbial consortia from Huancarhuaz hot spring (Peru) from sludge or in situ baiting cultured with or without sugarcane bagasse. According to the hydrolytic activities consortium T4 from in situ baiting was selected. It was cultivated in submerged fermentation at 65 °C, pH 6.5 for eight days using LB supplemented with sugar cane bagasse (SCB), pine wood sawdust (PWS), CMC, xylan of birchwood, or micro granular cellulose. Crude extract of culture supplemented with SCB (T4B) showed better endoglucanase and xylanase activities with higher activities at 75 °C and pH 6. In these conditions, cellulase activity was kept up to 57% after 1 h of incubation, while xylanase activity was up to 63% after 72 h. Furthermore, this crude extract released reduced sugars from pretreated SCB and PWS. According to metagenomic analysis of 16S rDNA, Geobacillus was the predominant genus. It was found thermostable genes: a type of endoglucanase (GH5), an endo-xylanase (GH10), and alkali xylanase (GH10) previously reported in Geobacillus sp. strains. Finally, Huancarhuaz hot spring harbors a genetic microbial diversity for lignocellulosic waste bioconversion in high temperatures, and the T4B consortium will be a promising source of novel extreme condition stable enzymes for the saccharification process.

A concerted enzymatic de-structuring of lignocellulosic materials using a compost-derived microbial consortia favoring the consolidated pretreatment and bio-saccharification

The robustness of microbial consortia isolated from compost habitat encompasses the complementary metabolism that aids in consolidated bioprocessing (CBP) of lignocellulosic biomass (LCB) by division of labor across the symbionts. Composting of organic waste is deemed to be an efficient way of carbon recycling, where the syntrophic microbial population exerts a concerted action of lignin and polysaccharide (hemicellulose and cellulose) component of plant biomass. The potential of this interrelated microorganism could be enhanced through adaptive laboratory evolution (ALE) with LCB for its desired functional capabilities. Therefore, in this study, microbial symbionts derived from organic compost was enriched on saw dust (SD) (woody biomass), aloe vera leaf rind (AVLR) (agro-industrial waste) and commercial filter paper (FP) (pure cellulose) through ALE under different conditions. Later, the efficacy of enriched consortium (EC) on consolidated pretreatment and bio-saccharification was determined based on substrate degradation, endo-enzymes profiling and fermentable sugar yield. Among the treatment sets, AVLR biomass treated with EC-5 has resulted in the higher degradation rate of lignin (47.01 ± 0.66%, w/w) and polysaccharides (45.87 ± 1.82%, w/w) with a total sugar yield of about 60.01 ± 4.24 mg/g. In addition, the extent of structural disintegration of substrate after EC-treatment was clearly deciphered by FTIR and XRD analysis. And the factors of Pearson correlation matrix reinforces the potency of EC-5 by exhibiting a strong positive correlation between AVLR degradation and the sugar release. Thus, a consortium based CBP could promote the feasibility of establishing a sustainable second generation biorefinery framework.

A critical assessment on scalable technologies using high solids loadings in lignocellulose biorefinery: challenges and solutions

The pretreatment and the enzymatic saccharification are the key steps in the extraction of fermentable sugars for further valorization of lignocellulosic biomass (LCB) to biofuels and value-added products via biochemical and/or chemical conversion routes. Due to low density and high-water absorption capacity of LCB, the large volume of water is required for its processing. Integration of pretreatment, saccharification, and co-fermentation has succeeded and well-reported in the literature. However, there are only few reports on extraction of fermentable sugars from LCB with high biomass loading (>10% Total solids-TS) feasible to industrial reality. Furthermore, the development of enzymatic cocktails can overcome technology hurdles with high biomass loading. Hence, a better understanding of constraints involved in the development of technology with high biomass loading can result in an economical and efficient yield of fermentable sugars for the production of biofuels and bio-chemicals with viable titer, rate, and yield (TRY) at industrial scale. The present review aims to provide a critical assessment on the production of fermentable sugars from lignocelluloses with high solid biomass loading. The impact of inhibitors produced during both pretreatment and saccharification has been elucidated. Moreover, the limitations imposed by high solid loading on efficient mass transfer during saccharification process have been elaborated.

Exploring the diversity of β-glucosidase: Classification, catalytic mechanism, molecular characteristics, kinetic models, and applications

High-value chemicals and energy-related products can be produced from biomass. Biorefinery technology offers a sustainable and cost-effective method for this high-value conversion. β-glucosidase is one of the key enzymes in biorefinery processes, catalyzing the production of glucose from aryl-glycosides and cello-oligosaccharides via the hydrolysis of β-glycosidic bonds. Although β-glucosidase plays a critical catalytic role in the utilization of cellulosic biomass, its efficacy is often limited by substrate or product inhibitions, low thermostability, and/or insufficient catalytic activity. To provide a detailed overview of β-glucosidases and their benefits in certain desired applications, we collected and summarized extensive information from literature and public databases, covering β-glucosidases in different glycosidase hydrolase families and biological kingdoms. These β-glucosidases show differences in amino acid sequence, which are translated into varying degrees of the molecular properties critical in enzymatic applications. This review describes studies on the diversity of β-glucosidases related to the classification, catalytic mechanisms, key molecular characteristics, kinetics models, and applications, and highlights several β-glucosidases displaying high stability, activity, and resistance to glucose inhibition suitable for desired biotechnological applications.

Computer-Aided Reconstruction and Application of Bacillus halodurans S7 Xylanase with Heat and Alkali Resistance

β-1,4-Endoxylanase is the most critical hydrolase for xylan degradation during lignocellulosic biomass utilization. However, its poor stability and activity in hot and alkaline environments hinder its widespread application. In this study, BhS7Xyl from Bacillus halodurans S7 was improved using a computer-aided design through isothermal compressibility (βT) perturbation engineering and by combining three thermostability prediction algorithms (ICPE-TPA). The best variant with remarkable improvement in specific activity, heat resistance (70 °C), and alkaline resistance (both pH 9.0 and 70 °C), R69F/E137M/E145L, exhibited a 4.9-fold increase by wild-type in specific activity (1368.6 U/mg), a 39.4-fold increase in temperature half-life (458.1 min), and a 57.6-fold increase in pH half-life (383.1 min). Furthermore, R69F/E137M/E145L was applied to the hydrolysis of agricultural waste (corncob and hardwood pulp) to efficiently obtain a higher yield of high-value xylooligosaccharides. Overall, the ICPE-TPA strategy has the potential to improve the functional performance of enzymes under extreme conditions for the high-value utilization of lignocellulosic biomass.

Green chemical and hybrid enzymatic pretreatments for lignocellulosic biorefineries: Mechanism and challenges

The greener chemical and enzymatic pretreatments for lignocellulosic biomasses are portraying a crucial role owing to their recalcitrant nature. Traditional pretreatments lead to partial degradation of lignin and hemicellulose moieties from the pretreated biomass. But it still restricts the enzyme accessibility for the digestibility towards the celluloses and the interaction of lignin-enzymes, nonproductively. Moreover, incursion of certain special chemical treatments and other lignin sulfonation techniques to the enzymatic pretreatment (hybrid enzymatic pretreatment) enhances the lignin structural modification, solubilization of the hemicelluloses and both saccharification and fermentation processes (SAF). This article concentrates on recent developments in various chemical and hybrid enzymatic pretreatments on biomass materials with their mode of activities. Furthermore, the issues on strategies of the existing pretreatments towards their industrial applications are highlighted, which could lead to innovative ideas to overcome the challenges and give guideline for the researchers towards the lignocellulosic biorefineries.

Expression and Characterization of Laccase Lac1 from Coriolopsis trogii Strain Mafic-2001 in Pichia pastoris and Its Degradation of Lignin

The laccase gene (Lac1) was cloned from Coriolopsis trogii strain Mafic-2001. Full-length sequence of Lac1 containing 11 exons and 10 introns is composed of 2140 nucleotides (nts). mRNA of Lac1 encoded for a protein of 517 aa. Nucleotide sequence of the laccase was optimized and expressed in Pichia pastoris X-33. SDS-PAGE analysis showed that the molecular weight of the purified recombinant laccase rLac1 was about 70 kDa. The optimum temperature and pH of rLac1 were 40 ℃ and 3.0, respectively. rLac1 showed high residual activity (90%) in the solutions after 1 h incubation at the pH ranging from 2.5 to 8.0. rLac1 maintained over 60% of laccase activity at the temperatures ranging from 20 to 60 °C, and kept higher than 50% of its activity at 40 °C for 2 h. The activity of rLac1 was promoted by Cu2+ and inhibited by Fe2+. Under optimal conditions, lignin degradation rates of rLac1 on the substrates of rice straw, corn stover, and palm kernel cake were 50.24%, 55.49%, and 24.43% (the lignin contents of substrates untreated with rLac1 were 100%), respectively. Treated with rLac1, the structures of agricultural residues (rice straw, corn stover, and palm kernel cake) were obviously loosened which was reflected by the analysis of scanning electron microscopy and Fourier transform infrared spectroscopy. Based on the specific activity of rLac1 on the degradation of lignin, rLac1 from Coriolopsis trogii strain Mafic-2001 has the potential for in-depth utilization of agricultural residues.

Key roles of β-glucosidase BglA for the catabolism of both laminaribiose and cellobiose in the lignocellulolytic bacterium Clostridium thermocellum

The thermophilic bacterium Clostridium thermocellum efficiently degrades polysaccharides into oligosaccharides. The metabolism of β-1,4-linked cello-oligosaccharides is initiated by three enzymes, i.e., the cellodextrin phosphorylase (Cdp), the cellobiose phosphorylase (Cbp), and the β-glucosidase A (BglA), in C. thermocellum. In comparison, how the oligosaccharides containing other kinds of linkage are utilized is rarely understood. In this study, we found that BglA could hydrolyze the β-1,3-disaccharide laminaribiose with much higher activity than that against the β-1,4-disaccharide cellobiose. The structural basis of the substrate specificity was analyzed by crystal structure determination and molecular docking. Genetic deletions of BglA and Cbp, respectively, and enzymatic analysis of cell extracts demonstrated that BglA is the key enzyme responsible for laminaribiose metabolism. Furthermore, the deletion of BglA can suppress the expression of Cbp and the deletion of Cbp can up-regulate the expression of BglA, indicating that BglA and Cbp have cross-regulation and BglA is also critical for cellobiose metabolism. These insights pave the way for both a fundamental understanding of metabolism and regulation in C. thermocellum and emphasize the importance of the degradation and utilization of polysaccharides containing β-1,3-linked glycosidic bonds in lignocellulose biorefinery.

Improving the cellobiose hydrolysis activity of glucose-stimulating β-glucosidase Bgl2A

β-Glucosidases with high catalytic activity and glucose tolerant properties possess promising applications in lignocellulose-based industries. To obtain enzymes possessing these properties, a semi-rational strategy was employed to engineer the glucose-stimulating β-glucosidase Bgl2A for high cellobiose hydrolysis activity. A total of 18 mutants were constructed. A22S, V224D, and A22S/V224D exhibited high specific activities of 272.06, 237.60, and 239.29 U/mg toward cellobiose, which were 2.5- to 2.8-fold of Bgl2A. A22S, V224D, and A22S/V224D exhibited increased k_cat values, which were 2.7- to 3.1-fold of Bgl2A. A22S and V224D maintained glucose-stimulating property, whereas A22S/V224D lost it. Using 150 g/L cellobiose as the substrate, the amount of glucose produced by A22S was the highest, yielding 129.70 g/L glucose after 3 h reaction at 35 °C. The synergistic effects of the engineered enzymes with commercial cellulase on hydrolyzing cellulose were investigated. Supplemented with the commercial cellulase and A22S, the highest glucose amount of 23.30 g/L was yielded from cellulose with hydrolysis rate of 21.02 %. Given its high cellobiose hydrolysis activity and glucose-stimulating properties, A22S can be used as a component of enzyme cocktail to match mesophilic cellulases for efficient cellulose hydrolysis.

Eight Up-Coming Biotech Tools to Combat Climate Crisis

Biotechnology has a high potential to substantially contribute to a low-carbon society. Several green processes are already well established, utilizing the unique capacity of living cells or their instruments. Beyond that, the authors believe that there are new biotechnological procedures in the pipeline which have the momentum to add to this ongoing change in our economy. Eight promising biotechnology tools were selected by the authors as potentially impactful game changers: (i) the Wood-Ljungdahl pathway, (ii) carbonic anhydrase, (iii) cutinase, (iv) methanogens, (v) electro-microbiology, (vi) hydrogenase, (vii) cellulosome and, (viii) nitrogenase. Some of them are fairly new and are explored predominantly in science labs. Others have been around for decades, however, with new scientific groundwork that may rigorously expand their roles. In the current paper, the authors summarize the latest state of research on these eight selected tools and the status of their practical implementation. We bring forward our arguments on why we consider these processes real game changers.

Integrated lactic acid production from lignocellulosic agricultural wastes under thermal conditions

The production of lactic acid (LA) from agricultural wastes attracts great attention because of the sustainability and abundance of lignocellulosic feedstocks, as well as the increasing demand for biodegradable polylactic acid. In this study, we isolated a thermophilic strain Geobacillus stearothermophilus 2H-3 for use in robust production of L-(+)LA under the optimal conditions of 60 °C, pH 6.5, which were consistent with the whole-cell-based consolidated bio-saccharification (CBS) process. Sugar-rich CBS hydrolysates derived from various agricultural wastes, including corn stover, corncob residue, and wheat straw, were used as the carbon sources for 2H-3 fermentation by directly inoculating 2H-3 cells into the CBS system, without intermediate sterilization, nutrient supplementation, or adjustment of fermentation conditions. Thus, we successfully combined two whole-cell-based steps into a one-pot successive fermentation process to efficiently produce LA with high optical purity (99.5%), titer (51.36 g/L), and yield (0.74 g/g_biomass). This study provides a promising strategy for LA production from lignocellulose through CBS and 2H-3 fermentation integration.

Employing Cationic Kraft Lignin as Additive to Enhance Enzymatic Hydrolysis of Corn Stalk

A water-soluble cationic kraft lignin (named JLQKL₅₀), synthesized by combining quaternization and crosslinking reactions, was used as an additive to enhance the enzymatic hydrolysis of dilute-alkali-pretreated corn stalk. The chemical constitution of JLQKL₅₀ was investigated by Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance (NMR) and ¹³C NMR spectroscopy, and elemental analysis. The enzymatic hydrolysis efficiency of corn stalk at solid content of 10% (w/v) was significantly improved from 70.67% to 78.88% after 24 h when JLQKL₅₀ was added at a concentration of 2 g/L. Meanwhile, the enzymatic hydrolysis efficiency after 72 h reached 91.11% with 10 FPU/g of cellulase and 97.92% with 15 FPU/g of cellulase. In addition, JLQKL₅₀ was found capable of extending the pH and temperature ranges of enzymatic hydrolysis to maintain high efficiency (higher than 70%). The decrease in cellulase activity under vigorous stirring with the addition of JLQKL₅₀ was 17.4%, which was much lower than that (29.7%) without JLQKL₅₀. The addition of JLQKL₅₀ reduced the nonproductive adsorption of cellulase on the lignin substrate and improved the longevity, dispersity, and stability of the cellulase by enabling electrostatic repulsion. Therefore, the enzymatic hydrolysis of the corn stalk was enhanced. This study paves the way for the design of sustainable lignin-based additives to boost the enzymatic hydrolysis of lignocellulosic biomass.

Genomic analysis of Paenibacillus macerans strain I6, which can effectively saccharify oil palm empty fruit bunches under nutrient-free conditions

The improper disposal of palm oil industrial waste has led to serious environmental pollution. In this study, we isolated Paenibacillus macerans strain I6, which can degrade oil palm empty fruit bunches generated by the palm oil industry in nutrient-free water, from bovine manure biocompost and sequenced its genome on PacBio RSII and Illumina NovaSeq 6000 platforms. We obtained 7.11 Mbp of genomic sequences with 52.9% GC content from strain I6. Strain I6 was phylogenetically closely related to P. macerans strains DSM24746 and DSM24 and was positioned close to the head of the branch containing strains I6, DSM24746, and DSM24 in the phylogenetic tree. We used the RAST (rapid annotation using subsystem technology) server to annotate the strain I6 genome and discovered genes related to biological saccharification; 496 genes were related to carbohydrate metabolism and 306 genes were related to amino acids and derivatives. Among them were carbohydrate-active enzymes (CAZymes), including 212 glycoside hydrolases. Up to 23.6% of the oil palm empty fruit bunches was degraded by strain I6 under anaerobic and nutrient-free conditions. Evaluation of the enzymatic activity of extracellular fractions of strain I6 showed that amylase and xylanase activity was highest when xylan was the carbon source. The high enzyme activity and the diversity in the associated genes may contribute to the efficient degradation of oil palm empty fruit bunches by strain I6. Our results indicate the potential utility of P. macerans strain I6 for lignocellulosic biomass degradation.

Evolving Robust and Interpretable Enzymes for the Bioethanol Industry

Obtaining a robust and applicable enzyme for bioethanol production is a dream for biorefinery engineers. Herein, we describe a general method to evolve an all-round and interpretable enzyme that can be directly employed in the bioethanol industry. By integrating the transferable protein evolution strategy InSiReP 2.0 (In Silico guided Recombination Process), enzymatic characterization for actual production, and computational molecular understanding, the model cellulase PvCel5A (endoglucanase II Cel5A from Penicillium verruculosum) was successfully evolved to overcome the remaining challenges of low ethanol and temperature tolerance, which primarily limited biomass transformation and bioethanol yield. Remarkably, application of the PvCel5A variants in both first- and second-generation bioethanol production processes (i. Conventional corn ethanol fermentation combined with the in situ pretreatment process; ii. cellulosic ethanol fermentation process) resulted in a 5.7-10.1 % increase in the ethanol yield, which was unlikely to be achieved by other optimization techniques.

Bioconversion of non-food corn biomass to polyol esters of fatty acid and single-cell oils

BACKGROUND

Lignocellulose is a valuable carbon source for the production of biofuels and biochemicals, thus having the potential to substitute fossil resources. Consolidated bio-saccharification (CBS) is a whole-cell-based catalytic technology previously developed to produce fermentable sugars from lignocellulosic agricultural wastes. The deep-sea yeast strain Rhodotorula paludigena P4R5 can produce extracellular polyol esters of fatty acids (PEFA) and intracellular single-cell oils (SCO) simultaneously. Therefore, the integration of CBS and P4R5 fermentation processes would achieve high-value-added conversion of lignocellulosic biomass.

RESULTS

The strain P4R5 could co-utilize glucose and xylose, the main monosaccharides from lignocellulose, and also use fructose and arabinose for PEFA and SCO production at high levels. By regulating the sugar metabolism pathways for different monosaccharides, the strain could produce PEFA with a single type of polyol head. The potential use of PEFA as functional micelles was also determined. Most importantly, when sugar-rich CBS hydrolysates derived from corn stover or corncob residues were used to replace grain-derived pure sugars for P4R5 fermentation, similar PEFA and SCO productions were obtained, indicating the robust conversion of non-food corn plant wastes to high-value-added glycolipids and lipids. Since the produced PEFA could be easily collected from the culture via short-time standing, we further developed a semi-continuous process for PEFA production from corncob residue-derived CBS hydrolysate, and the PEFA titer and productivity were enhanced up to 41.1 g/L and 8.22 g/L/day, respectively.

CONCLUSIONS

Here, we integrated the CBS process and the P4R5 fermentation for the robust production of high-value-added PEFA and SCO from non-food corn plant wastes. Therefore, this study suggests a feasible way for lignocellulosic agro-waste utilization and the potential application of P4R5 in industrial PEFA production.

Efficient Co-Production of Xylooligosaccharides and Glucose from Vinegar Residue by Biphasic Phenoxyethanol-Maleic Acid Pretreatment

A new biphasic organic solvent, phenoxyethanol-maleic acid, was carried out to pretreat and fractionate vinegar residue into glucan, xylan and lignin under mild conditions. Additional effects of key factors, temperature and phenoxyethanol concentration, on vinegar residue, were evaluated. Under the biphasic system (0.5% maleic acid, 60% phenoxyethanol), 140 °C cooking vinegar residue for 1 h, 80.91% of cellulose retention in solid residue, 75.44% of hemicellulose removal and 69.28% of lignin removal were obtained. Optimal identified conditions resulted in maximum XOS of 47.3%. Then, the solid residue was enzymatically digested with a glucose yield of 82.67% at 72 h with the addition of 2.5 g/L bovine serum albumin. Finally, the residue was characterized by SEM, FTIR, XRD and BET analysis. This work demonstrated the phenoxyethanol-maleic acid pretreatment yielded XOS, fermentable sugar, and lignin with high processibility.

Advances and perspectives on mass transfer and enzymatic hydrolysis in the enzyme-mediated lignocellulosic biorefinery: A review

Enzymatic hydrolysis is a critical process for the cellulase-mediated lignocellulosic biorefinery to produce sugar syrups that can be converted into a whole range of biofuels and biochemicals. Such a process operating at high-solid loadings (i.e., scarcely any free water or roughly ≥ 15% solids, w/w) is considered more economically feasible, as it can generate a high sugar concentration at low operation and capital costs. However, this approach remains restricted and incurs "high-solid effects", ultimately causing the lower hydrolysis yields with increasing solid loadings. The lack of available water leads to a highly viscous system with impaired mixing that exhibits strong transfer resistance and reaction limitation imposed on enzyme action. Evidently, high-solid enzymatic hydrolysis involves multi-scale mass transfer and multi-phase enzyme reaction, and thus requires a synergistic perspective of transfer and biotransformation to assess the interactions among water, biomass components, and cellulase enzymes. Porous particle characteristics of biomass and its interface properties determine the water form and distribution state surrounding the particles, which are summarized in this review aiming to identify the water-driven multi-scale/multi-phase bioprocesses. Further aided by the cognition of rheological behavior of biomass slurry, solute transfer theories, and enzyme kinetics, the coupling effects of flow-transfer-reaction are revealed under high-solid conditions. Based on the above basic features, this review lucidly explains the causes of high-solid hydrolysis hindrances, highlights the mismatched issues between transfer and reaction, and more importantly, presents the advanced strategies for transfer and reaction enhancements from the viewpoint of process optimization, reactor design, as well as enzyme/auxiliary additive customization.

Engineering Trichoderma reesei for the hyperproduction of cellulose induced protein 1 (Cip1) on a sophorose-containing inducer to efficiently saccharify alkali-pretreated corn stover

Trichoderma reesei was induced to produce cellulase by a combination of glucose and β-disaccharide; however, lower levels of auxiliary proteins for degrading lignocellulosic biomass were detected by iTRAQ analysis compared with cellulose as an inducer, especially cellulose induced protein 1 (CIP1). In this study, A pdc1 promoter-driven overexpression of the endogenous Trcip1 gene was observed in T. reesei Rut C30, and the Trcip1 transcription levels of the two transformants, T. reesei OE-cip1-1 and OE-cip1-2, demonstrated 31.2- and 164.6-fold increases, respectively, but there was no significant change in cellobiohydrolase, endoglucanase and filter paper activity at 48 h. The crude enzyme was then used to hydrolyze corn stover. For T. reesei OE-cip1-1 and OE-cip1-2, the hydrolysis efficiency increased by 25.0 and 28.6% with a solid loading of 5% at 2 h, respectively. Simultaneously, 85.5 and 85.2 g/L glucose were released using a cellulase cocktail at high solid loading (20%), and these glucose release rates were significantly greater than that of T. reesei Rut C30 cellulase (77.4 g/L) at 120 h. Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that the enhanced hydrolysis efficiency was primarily triggered by the decrease in the crystallinity of lignocellulose, and the fiber structure had varying degrees of loosening and disintegration.

Efficient co-production of xylooligosaccharides and glucose from lignocelluloses by acid/pentanol pretreatment: Synergetic role of lignin removal and inhibitors

A novel technology for co-production of xylooligosaccharides (XOS) and glucose from Monterey pine sawdust and wheat straw was introduced using dilute acid (DA)/pentanol pretreatment. Effects of pretreatment severity (PS), lignin removal, and inhibitors with byproduct concentrations on XOS production were investigated. Optimal identified conditions (PS: 3.71; 170 °C, 45 min) resulted in maximum XOS of 48.65 % (pine sawdust) and 46.85 % (wheat straw), due to appropriate lignin removal (pine sawdust, 88.5 %; wheat straw, 89.7 %) and formation of small amounts of inhibitors and byproducts. Enzymatic hydrolysis of optimal pretreated solid residues yielded 88.65 % and 93.34 % glucose in pine sawdust and wheat straw, respectively. Biomass characterization revealed that DA/pentanol pretreatment enhanced porosity and pore size along with removal of amorphous fractions in both samples, thereby increasing cellulose accessibility and glucose yield. This study demonstrated lignin removal and low formation of inhibitors and byproducts, effectively enhancing XOS and glucose production from lignocellulosic biomass.

Lignocellulose dissociation with biological pretreatment towards the biochemical platform: A review

Lignocellulose utilization has been gaining great attention worldwide due to its abundance, accessibility, renewability and recyclability. Destruction and dissociation of the cross-linked, hierarchical structure within cellulose hemicellulose and lignin is the key procedure during chemical utilization of lignocellulose. Of the pretreatments, biological treatment, which can effectively target the complex structures, is attractive due to its mild reaction conditions and environmentally friendly characteristics. Herein, we report a comprehensive review of the current biological pretreatments for lignocellulose dissociation and their corresponding degradation mechanisms. Firstly, we analyze the layered, hierarchical structure of cell wall, and the cross-linked network between cellulose, hemicellulose and lignin, then highlight that the cracking of β-aryl ether is considered the key to lignin degradation because of its dominant position. Secondly, we explore the effect of biological pretreatments, such as fungi, bacteria, microbial consortium, and enzymes, on substrate structure and degradation efficiency. Additionally, combining biological pretreatment with other methods (chemical methods and catalytic materials) may reduce the time necessary for the whole process, which also help to strengthen the lignocellulose dissociation efficiency. Thirdly, we summarize the related applications of lignocellulose, such as fuel production, chemicals platform, and bio-pulping, which could effectively alleviate the energy pressure through bioconversion into high value-added products. Based on reviewing of current progress of lignocellulose pretreatment, the challenges and future prospects are emphasized. Genetic engineering and other technologies to modify strains or enzymes for improved biotransformation efficiency will be the focus of future research.

Impacts of composting duration on physicochemical properties and microbial communities during short-term composting for the substrate for oyster mushrooms

A short-term composting process to prepare substrate is an effective way to cultivate oyster mushrooms (Pleurotus spp.), which can increase the yield of mushrooms and lower the rate of contamination in non-industrialized cultivation. Moreover, it is different from the traditional composting processes for fertilizers and lacks systematic study, such as microbial succession and compost quality. In this study, a series of different tests of composting duration (0, 2, 4 and 5 d) were performed. A composting duration of 4-5 d over 58 °C was suitable for mushroom cultivation based on the biological efficiency (BE) range of 69.76-73.41 % and the contamination rate of 0 %. The content of total carbon (TC) continuously decreased during composting, while the content of total nitrogen (TN) reacted in an opposite matter. The final TN and C/N ratios were 1.89 % and 28/1, respectively, which fell well within the optimal range of nutritional requirements for oyster mushroom cultivation. The composting bacteria were more diverse than the fungal species. Caldibacillus, Thermobispora, Thermopolyspora, Thermobacillus and Ureibacillus were the predominant bacterial genera during the thermophilic stage. Co-occurrence patterns of microbial communities and physicochemical properties were performed using a network analysis, which indicated that bacteria can play more efficient roles than fungi in the degradation of organic matter. The structural equation model showed that composting duration significantly affected bacterial diversity, lignocellulose degradation rates, and BE. The correlations between bioinformatics parameters with composting characters and agronomic traits were determined by the Mantel test and showed that the induction of bacterial diversity over time rapidly activated carbon metabolism during short-term composting. This study provides a new idea of agro-waste composting for mushroom cultivation.

Clostridium as microbial cell factory to enable the sustainable utilization of three generations of feedstocks

The sustainable production of chemicals and biofuels from non-fossil carbon sources is considered key to reducing greenhouse gas (GHG) emissions. Clostridium sp. can convert various substrates, including the 1st-generation (biomass crops), the 2nd-generation (lignocellulosic biomass), and the 3rd-generation (C1 gases) feedstocks, into high-value products, which makes Clostridia attractive for biorefinery applications. However, the complexity of lignocellulosic catabolism and C1 gas utilization make it difficult to construct efficient production routes. Accordingly, this review highlights the advances in the development of three generations of feedstocks with Clostridia as cell factories. At the same time, more attention was given to using agro-industrial wastes (lignocelluloses and C1 gases) as the feedstocks, for which metabolic and process engineering efforts were comprehensively analyzed. In addition, the challenges of using agro-industrial wastes are also discussed. Lastly, several new synthetic biology tools and regulatory strategies are emphasized as promising technologies to be developed to address the aforementioned challenges in Clostridia and realize the efficient utilization of agro-industrial wastes.

Deciphering Cellodextrin and Glucose Uptake in Clostridium thermocellum

Sugar uptake is of great significance in industrially relevant microorganisms. Clostridium thermocellum has extensive potential in lignocellulose biorefineries as an environmentally prominent, thermophilic, cellulolytic bacterium. The bacterium employs five putative ATP-binding cassette transporters which purportedly take up cellulose hydrolysates. Here, we first applied combined genetic manipulations and biophysical titration experiments to decipher the key glucose and cellodextrin transporters. In vivo gene inactivation of each transporter and in vitro calorimetric and nuclear magnetic resonance (NMR) titration of each putative sugar-binding protein with various saccharides supported the conclusion that only transporters A and B play the roles of glucose and cellodextrin transport, respectively. To gain insight into the structural mechanism of the transporter specificities, 11 crystal structures, both alone and in complex with appropriate saccharides, were solved for all 5 putative sugar-binding proteins, thus providing detailed specific interactions between the proteins and the corresponding saccharides. Considering the importance of transporter B as the major cellodextrin transporter, we further identified its cryptic, hitherto unknown ATPase-encoding gene as clo1313_2554, which is located outside the transporter B gene cluster. The crystal structure of the ATPase was solved, showing that it represents a typical nucleotide-binding domain of the ATP-binding cassette (ABC) transporter. Moreover, we determined that the inducing effect of cellobiose (G2) and cellulose on cellulosome production could be eliminated by deletion of transporter B genes, suggesting the coupling of sugar transport and regulation of cellulosome components. This study provides key basic information on the sugar uptake mechanism of C. thermocellum and will promote rational engineering of the bacterium for industrial application.

Study on the Sugar-Producing Effect of High-Temperature Anaerobic Straw Biosaccharification Strain

The utilization of straw waste cellulose will be beneficial by economic, social, and environmental means. The present study sought to screen the high-efficiency cellulose sugar-producing strain from corn straw. The 16S high-throughput sequencing method and the combination of morphological, physiological, and biochemical characteristics of the strain confirmed the strain to be Clostridium thermocellum, which was named Clostridium thermocellum FC811. Moreover, the single factor experiment was conducted to investigate the effect of environmental factors on saccharification efficiency. The optimal saccharification conditions of cellulose saccharification of FC811 strain selected through response surface analysis were as follows: temperature of 58.9 °C, pH of 7.21, culture time of 6.60 d, substrate concentration of 5.01 g/L, and yeast powder concentration of 2.15 g/L. The soluble sugar yield was 3.11 g/L, and the conversion rate of reducing sugar was 62.2%. This study will provide a reference for resource and energy utilization of straw materials, simultaneous fermentation of sugar and hydrogen production, and their large-scale production and application.

Lignin removal improves xylooligosaccharides production from poplar by acetic acid hydrolysis

Organic acid hydrolysis is a potential method for xylooligosaccharides (XOS) production from lignocelluloses. However, the effect of lignin content on XOS production using organic acid hydrolysis remains unclear. In this work, the effect of delignification on XOS production from poplar by acetic acid (AC) hydrolysis was investigated. Hydrogen peroxide-acetic acid (HPAC) pretreatment catalyzed by 0-200 mM H₂SO₄ (HPAC0-HPAC200) removed 21.6-86.5% of lignin in poplar. HPAC pretreatment increased the xylan accessibility to AC solution, thus increasing the xylan removal during AC hydrolysis. An appropriate delignification (61.7%) resulted in the highest XOS yield of 37.4% by AC hydrolysis, increased by 29.9% compared to the optimal XOS yield (28.8%) from raw poplar. After alkaline post-incubation, the glucose yield of poplar residue rose from 57.1% to 78.6%. This work developed a delignification process to efficiently improve XOS and monosaccharides production from poplar.

Dissolved xylan inhibits cellulosome-based saccharification by binding to the key cellulosomal component of Clostridium thermocellum

Polysaccharides derived from lignocellulose are promising sustainable carbon sources. Cellulosome is a supramolecular machine integrating multi-function enzymes for effective lignocellulose bio-saccharification. However, how various non-cellulose components of lignocellulose affect the cellulosomal saccharification is hitherto unclear. This study first investigated the stability and oxygen sensitivity of the cellulosome from Clostridium thermocellum during long-term saccharification process. Then, the differential inhibitory effects of non-cellulose components, including lignin, xylan, and arabinoxylan, on the cellulosome-based saccharification were determined. The results showed that lignin played inhibitory roles by non-productively adsorbing extracellular proteins of C. thermocellum. Differently, arabinoxylan preferred to bind with the cellulosomal components. Almost no adsorption of cellulosomal proteins on solid xylan was detected. Instead, xylan in water-dissolved form interacted with the cellulosomal proteins, especially the key exoglucanase Cel48S, leading to the xylan inhibitory effect. Compared to xylan, xylooligosaccharides influenced the cellulosome activity slightly. Hence, this work demonstrates that the timely hydrolysis or removal of dissolved xylan is important for cellulosome-based lignocellulose saccharification.

In vivo Functional Characterization of Hydrophilic X2 Modules in the Cellulosomal Scaffolding Protein

As part of free cellulases or scaffolding proteins in cellulosomes, the hydrophilic non-catalytic X2 module is widely distributed in cellulolytic Clostridia or other Firmicutes bacteria. Previous biochemical studies suggest that X2 modules might increase the solubility and substrate binding affinity of X2-bearing proteins. However, their in vivo biological functions remain elusive. Here we employed CRISPR-Cas9 editing to genetically modify X2 modules by deleting the conserved motif (NGNT) from the CipC scaffoldin. Both single and double X2 mutants (X2-N: near the N terminus of CipC; X2-C: near the C terminus of CipC) presented similar stoichiometric compositions in isolated cellulosomes as the wildtype strain (WT). These X2 mutants had an elongated adaptation stage during growth on cellulose compared to cellobiose. Compared to WT, the double mutant ΔX2-NC reduced cellulose degradation by 15% and the amount of released soluble sugars by 63%. Since single X2 mutants did not present such obvious physiological changes as ΔX2-NC, there seems to be a functional redundancy between X2 modules in CipC. The in vivo adhesion assay revealed that ΔX2-NC decreased cell attachment to cellulose by 70% but a weaker effect was also overserved in single X2 mutants. These results highlight the in vivo biological role of X2 in increasing cellulose degradation efficiency by enhancing the binding affinity between cells and cellulose, which provides new perspectives for microbial engineering.

Novel, recyclable Brønsted acidic deep eutectic solvent for mild fractionation of hemicelluloses

Acidic deep eutectic solvents (DESs) are promising media for lignin valorization and cellulose conversion due to their good ability in efficient deconstruction of plant cell wall. However, hemicellulose extraction from lignocellulose using acidic DESs remains a challenge. Herein, novel and green Brønsted acidic DESs (BDESs) were synthesized from natural organic acids and common polyols and successively adopted to deconstruct corncob for mild fractionation of hemicelluloses. Oxalic acid (OA)-based BDESs were preferred for corncob processing due to the high solubility of xylan. The results revealed that the suitable acidity of DESs and mild temperature effectively avoided the over-degradation of hemicelluloses. The chemical composition and structural features of the recovered hemicelluloses were investigated systematically. Moreover, after ethylene glycol (EG)-OA BDES was recycled and reused three times, the extraction still resulted in a satisfactory hemicellulose yield. The novel and eco-friendly processing offers a practical and sustainable route for hemicellulose extraction in acidic condition.

Recent advances and sustainable development of biofuels production from lignocellulosic biomass

Many countries in the world are facing the demand for non-renewable fossil fuels because of overpopulation and economic boom. To reduce environmental pollution and zero carbon emission, the conversion of biomass into biofuels has paid better attention and is considered to be an innovative approach. A diverse raw material has been utilized as feedstock for the production of biofuel, depending on the availability of biomass, cost-effectiveness, and their geographic location. Among the different raw materials, lignocellulosic biomass has fascinated many researchers around the world. The current review discovers the potential application of lignocellulosic biomass for the production of biofuels. Various pretreatment methods have been widely used to increase the hydrolysis rate and accessibility of biomass. This review highlights recent advances in pretreatment methodologies for the enhanced production of biofuels. Detailed descriptions of the mechanism of biomass processing pathway, optimization, and modeling study have been discussed.

Global status of lignocellulosic biorefinery: Challenges and perspectives

The bioprocessing of lignocellulosic biomass to produce bio-based products under biorefinery setup is gaining global attention. The economic viability of this biorefinery would be inclined by the efficient bioconversion of all three major constituents of lignocellulosic biomass i.e. cellulose, hemicellulose, and lignin for value-added biochemicals and biofuels production. Although the lignocellulosic biorefinery setup has a clear value proposition, the commercial success at the industrial scale is still inadequate. This can be attributed mainly to irregular biomass supply chain, market uncertainties, and scale-up challenges. Global research efforts are underway by public and private sectors to get deeper market penetration. A comprehensive account of important factors, limitations, and propositions are worth consideration for the commercial success of lignocellulosic biorefineries. In this article, the importance of integration of lignocellulosic biorefineries with existing petrochemical refineries, the technical challenges of industrialization, SWOT analysis, and future directions have been reviewed.

Smart sustainable biorefineries for lignocellulosic biomass

Lignocellulosic biomass (LCB) is considered as a sustainable feedstock for a biorefinery to generate biofuels and other bio-chemicals. However, commercialization is one of the challenges that limits cost-effective operation of conventional LCB biorefinery. This article highlights some studies on the sustainability of LCB in terms of cost-competitiveness and environmental impact reduction. In addition, the development of computational intelligence methods such as Artificial Intelligence (AI) as a tool to aid the improvement of LCB biorefinery in terms of optimization, prediction, classification, and decision support systems. Lastly, this review examines the possible research gaps on the production and valorization in a smart sustainable biorefinery towards circular economy.

Fungal lignocellulolytic enzymes and lignocellulose: A critical review on their contribution to multiproduct biorefinery and global biofuel research

The continuous increase in the global energy demand has diminished fossil fuel reserves and elevated the risk of environmental deterioration and human health. Biorefinery processes involved in producing bio-based energy-enriched chemicals have paved way to meet the energy demands. Compared to the thermochemical processes, fungal system biorefinery processes seems to be a promising approach for lignocellulose conversion. It also offers an eco-friendly and energy-efficient route for biofuel generation. Essentially, ligninolytic white-rot fungi and their enzyme arsenals degrade the plant biomass into structural constituents with minimal by-products generation. Hemi- or cellulolytic enzymes from certain soft and brown-rot fungi are always favoured to hydrolyze complex polysaccharides into fermentable sugars and other value-added products. However, the cost of saccharifying enzymes remains the major limitation, which hinders their application in lignocellulosic biorefinery. In the past, research has been focused on the role of lignocellulolytic fungi in biofuel production; however, a cumulative study comprising the contribution of the lignocellulolytic enzymes in biorefinery technologies is still lagging. Therefore, the overarching goal of this review article is to discuss the major contribution of lignocellulolytic fungi and their enzyme arsenal in global biofuel research and multiproduct biorefinery.

Improvement of endoglucanase production by Aspergillus brasiliensis in solid-state fermentation using cupuaçu (Theobroma grandiflorum) residue as substrate

AIMS

Optimize the production of Aspergillus brasiliensis endoglucanase in a solid-phase bioprocess using cupuaçu shell as substrate.

METHODS AND RESULTS

The shells were supplemented with nitrogen and phosphorous and used as a substrate. The centesimal and inorganic composition of the residue was determined, and found to be rich in fibres, and possessed essential elements for fungal growth. In the initial cultivation of A. brasiliensis, endoglucanase activity of 7.35 U g^-1 was obtained. A factorial experimental design was used to determine the most significant variables for the bioprocess. The interactions between moisture, temperature and nitrogen source were noteworthy (p < 0.05). From the rotational central composite design, the optimization of temperature and nitrogen supplementation was obtained, and this reached 40.50 U g^-1 , which is an increase of more than five times the value obtained initially. The enzymatic extract was applied as the biocatalyst in the hydrolysis of cupuaçu shells and, after 48 h, it was possible to observe the production of reducing sugars.

CONCLUSIONS

Cupuaçu shell can be used as a substrate for endoglucanase production by A. brasiliensis. The process was optimized for the cultivation temperature and the nitrogen source. The enzymatic extract can be applied in the hydrolysis of lignocellulosic biomass.

SIGNIFICANCE AND IMPACT OF THE STUDY

Cupuaçu shells can be used to produce cellulases, a product of high added value that can generate economic and environmental benefits for communities and companies producing derivatives of the cupuaçu fruit.

Two-step acetic acid/sodium acetate and xylanase hydrolysis for xylooligosaccharides production from corncob

At present, xylooligosaccharides (XOS) from corncob using acid-base conjugate system has not been reported. In this study, XOS production from corncob by two-step acetic acid/sodium acetate (AC/SA) conjugate system hydrolysis and xylanase hydrolysis was optimized, and monosaccharides were subsequently produced from corncob residues by cellulase hydrolysis. The XOS of 19.9 g/L was obtained from corncob (10%, w/v) using 0.15 M AC/SA hydrolysis at a molar ratio of 3.0 at 170 °C for 60 min, followed by xylanase hydrolysis. The second-step AC/SA hydrolysis of hydrolyzed corncob (10%, w/v) produced 3.1 g/L of XOS. Finally, the maximum XOS yield of 74.8% (based on xylan in corncob) was achieved, which is the highest yield among yields reported previously. The purity of XOS was high, whereas the contents of by-products were very low. This work presents a novel and promising strategy for co-production of XOS and monosaccharides from corncob without xylan isolation and purification.

Selection of Superior Yeast Strains for the Fermentation of Lignocellulosic Steam-Exploded Residues

The production of lignocellulosic ethanol calls for a robust fermentative yeast able to tolerate a wide range of toxic molecules that occur in the pre-treated lignocellulose. The concentration of inhibitors varies according to the composition of the lignocellulosic material and the harshness of the pre-treatment used. It follows that the versatility of the yeast should be considered when selecting a robust strain. This work aimed at the validation of seven natural Saccharomyces cerevisiae strains, previously selected for their industrial fitness, for their application in the production of lignocellulosic bioethanol. Their inhibitor resistance and fermentative performances were compared to those of the benchmark industrial yeast S. cerevisiae Ethanol Red, currently utilized in the second-generation ethanol plants. The yeast strains were characterized for their tolerance using a synthetic inhibitor mixture formulated with increasing concentrations of weak acids and furans, as well as steam-exploded lignocellulosic pre-hydrolysates, generally containing the same inhibitors. The eight non-diluted liquors have been adopted to assess yeast ability to withstand bioethanol industrial conditions. The most tolerant S. cerevisiae Fm17 strain, together with the reference Ethanol Red, was evaluated for fermentative performances in two pre-hydrolysates obtained from cardoon and common reed, chosen for their large inhibitor concentrations. S. cerevisiae Fm17 outperformed the industrial strain Ethanol Red, producing up to 18 and 39 g/L ethanol from cardoon and common reed, respectively, with ethanol yields always higher than those of the benchmark strain. This natural strain exhibits great potential to be used as superior yeast in the lignocellulosic ethanol plants.

Bioconversion of Lignocellulosic Biomass into Value Added Products under Anaerobic Conditions: Insight into Proteomic Studies

Production of biofuels and other value-added products from lignocellulose breakdown requires the coordinated metabolic activity of varied microorganisms. The increasing global demand for biofuels encourages the development and optimization of production strategies. Optimization in turn requires a thorough understanding of the microbial mechanisms and metabolic pathways behind the formation of each product of interest. Hydrolysis of lignocellulosic biomass is a bottleneck in its industrial use and often affects yield efficiency. The accessibility of the biomass to the microorganisms is the key to the release of sugars that are then taken up as substrates and subsequently transformed into the desired products. While the effects of different metabolic intermediates in the overall production of biofuel and other relevant products have been studied, the role of proteins and their activity under anaerobic conditions has not been widely explored. Shifts in enzyme production may inform the state of the microorganisms involved; thus, acquiring insights into the protein production and enzyme activity could be an effective resource to optimize production strategies. The application of proteomic analysis is currently a promising strategy in this area. This review deals on the aspects of enzymes and proteomics of bioprocesses of biofuels production using lignocellulosic biomass as substrate.

Soybean hulls as carbohydrate feedstock for medium to high-value biomolecule production in biorefineries: A review

Soybean is one of the major world crops, with an annual production of 359 million tons. Each ton of processed soybean generates 50-80 kg of soybean hulls (SHs), representing 5-8% of the whole seed. Due to environmental concerns and great economic potential, the search of SHs re-use solutions are deeply discussed. The lignocellulosic composition of SHs has attracted the attention of the scientific and productive sector. Recently, some studies have reported the use of SHs in the production of medium to high value-added molecules, with potential applications in food and feed, agriculture, bioenergy, and other segments. This review presents biotechnological approaches and processes for the management and exploitation of SHs, including pre-treatment methods and fermentation techniques, for the production of different biomolecules. Great potentialities and innovations were found concerning SH exploration and valorisation of the soybean chain under a biorefinery and circular bioeconomy optic.

Coordinated β-glucosidase activity with the cellulosome is effective for enhanced lignocellulose saccharification

Consolidated bio-saccharification (CBS) technology employs cellulosome-producing bacterial cells, rather than fungal cellulases, as biocatalysts for cost-effective production of lignocellulosic sugars. Extracellular β-glucosidase (BGL) expression in the whole-cell arsenal is indispensable, due to severe cellobiose inhibition of the cellulosome. However, high-level BGL expression in Clostridium thermocellum is challenging, and the optimal BGL production level for efficient cellulose saccharification is currently unknown. Herein, we obtained new CBS biocatalysts by transforming BGL-expressing plasmids into C. thermocellum, which produced abundant BGL proteins and hydrolyzed cellulose effectively. The optimal ratio of extracellular BGL-to-cellulosome activity was determined to be in a range of 5.5 to 21.6. Despite the critical impact of BGL, both excessive BGL expression and its assembly on the cellulosome via type I cohesin-dockerin interaction led to reduced cellulosomal activity, which further confirmed the importance of coordinated BGL expression with the cellulosome. This study will further promote industrial CBS application in lignocellulose conversion.

NMR chemical shift assignments of a module of unknown function in the cellulosomal secondary scaffoldin ScaF from Clostridium thermocellum

The cellulosome is a highly efficient cellulolytic complex containing cellulolytic enzymes and non-catalytic subunits, i.e. scaffoldins, which are assembled by the interactions between the dockerin modules of the enzymes and the cohesin modules of the primary scaffoldins. The cellulosome attaches to the cell surface via the S-layer homology (SLH) modules of the anchoring scaffoldins. Clostridium thermocellum DSM1313 is a thermophilic cellulosome-producing bacterium with great potential in lignocellulose bioconversion and biofuel production. The bacterium contains four anchoring scaffoldins ScaB, ScaC, ScaD and ScaF, among which ScaF is the only one that contains an additional module of unknown function (ScaF-X) between the cohesin and SLH modules. The gene of ScaF is located outside the scaffoldin gene cluster of scaA, scaB, scaC and scaD. Previous studies showed unique regulation properties and function of ScaF compared to other anchoring scaffoldins, which might be related to the additional ScaF-X module. Here we report the NMR chemical shift assignments of ScaF-X from C. thermocellum DSM1313. The well-dispersed NMR spectrum and the secondary structure prediction based on the chemical shifts of ScaF-X indicated that ScaF-X is a well-folded protein module. The chemical shift assignments provide the basis for future studies on the structure of this module and its function in cellulosomes.

Emerging trends in high-solids enzymatic saccharification of lignocellulosic feedstocks for developing an efficient and industrially deployable sugar platform

For the techno-commercial success of any lignocellulosic biorefinery, the cost-effective production of fermentable sugars for the manufacturing of bio-based products is indispensable. High-solids enzymatic saccharification (HSES) is a straightforward approach to develop an industrially deployable sugar platform. Economic incentives such as reduced capital and operational expenditure along with environmental benefits in the form of reduced effluent discharge makes this strategy more lucrative for exploitation. However, HSES suffers from the drawback of non-linear and disproportionate sugar yields with increased substrate loadings. To overcome this bottleneck, researchers tend to perform HSES at high enzyme loadings. Nonetheless, the production costs of cellulases are one of the key contributors that impair the entire process economics. This review highlights the relentless efforts made globally to attain a high-titer of sugars and their fermentation products by performing efficient HSES at low cellulase loadings. In this context, technical innovations such as advancements in new pretreatment strategies, next-generation cellulase cocktails, additives, accessory enzymes, novel reactor concepts and enzyme recycling studies are especially showcased. This review further covers new insights, learnings and prospects in the area of lignocellulosic bioprocessing.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

Succession of the microbial communities and function prediction during short-term peach sawdust-based composting

Short-term composting of raw materials for preparing oyster mushroom cultivation media is widely used in China, and its microbial mechanism needs to be further studied. 11-days' peach sawdust-based composting was performed to evaluate material conversion and microbial succession using physicochemical analysis and 16S rRNA and ITS sequencing. Composting bacteria demonstrated much higher abundance than fungi. Firmicutes, Actinobacteriota, and Proteobacteria were the dominant bacterial phyla, while most of fungal species belonged to Ascomycota. Moisture was the key factor at the beginning, while total nitrogen, temperature, and lignin became main influencing factors for composting maturity. Actinobacteriota, Firmicutes, and Proteobacteria of bacterial phyla, Eurotiomycetes and Sordariomycetes of fungal classes involved in lignocellulosic degradation. Bacterial function prediction analysis showed that carbohydrate metabolism and amino acid metabolism were the main metabolic pathways. These results confer a better understanding of material and microbial succession during short-term composting and also provide valuable utilization in mushroom industry.

Chemo-enzymatic approaches for consolidated bioconversion of Saccharum spontaneum biomass to ethanol-biofuel

A novel strategy involving sodium dodecylsulfate (SDS) (SDS assisted tris (2-hydroxyethyl) methyl- ammonium methyl sulphate ([TMA][MeSO₄], ionic liquid) pretreatment of Saccharum spontaneum biomass (SSB) following its enzymatic saccharification, and conversion into ethanol-biofuel in a consolidated bioprocess (CBP) was developed. Ionic liquid stable enzyme preparation developed from Bacillus subtilis G₂ was used for saccharification. Optimized pretreatment and saccharification variables enhanced the sugar yield (2.35-fold), which was fermented to ethanol content of 104.42 mg/g biomass with an efficiency of 35.73%. The pretreated biomass was examined for textural/ultrastructural alterations by scanning electron microscopy (SEM), ¹H/¹³C nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), surface area measurements, water retention value, and cellulase adsorption isotherms. The combined [TMA][MeSO₄] and SDS pretreatment disrupted the lignocellulosic microfibrils, and increased the porosity and surface area. The study provides new mechanistic insights on combined IL and surfactant pretreatment of biomass for its efficient conversion to biofuel.

Thermophilic microbial deconstruction and conversion of natural and transgenic lignocellulose

The potential to convert renewable plant biomasses into fuels and chemicals by microbial processes presents an attractive, less environmentally intense alternative to conventional routes based on fossil fuels. This would best be done with microbes that natively deconstruct lignocellulose and concomitantly form industrially relevant products, but these two physiological and metabolic features are rarely and simultaneously observed in nature. Genetic modification of both plant feedstocks and microbes can be used to increase lignocellulose deconstruction capability and generate industrially relevant products. Separate efforts on plants and microbes are ongoing, but these studies lack a focus on optimal, complementary combinations of these disparate biological systems to obtain a convergent technology. Improving genetic tools for plants have given rise to the generation of low-lignin lines that are more readily solubilized by microorganisms. Most focus on the microbiological front has involved thermophilic bacteria from the genera Caldicellulosiruptor and Clostridium, given their capacity to degrade lignocellulose and to form bio-products through metabolic engineering strategies enabled by ever-improving molecular genetics tools. Bioengineering plant properties to better fit the deconstruction capabilities of candidate consolidated bioprocessing microorganisms has potential to achieve the efficient lignocellulose deconstruction needed for industrial relevance.