Challenges and perspectives of green-like lignocellulose pretreatments selectable for low-cost biofuels and high-value bioproduction

Hydrothermal formation mechanism of lignocellulose-derived carbon dots: From sawdust to carbon nanomaterials with blue fluorescence

The conversion of lignocellulose into fluorescent lignocellulose-derived carbon dots (LCDs) via hydrothermal carbonization (HTC) has attracted significant attention. However, the degradation pathways of lignocellulose components, their contributions to LCDs formation, and the temporal evolution of LCDs' formation remain unclear. Given that HTC conditions influence LCDs' structure and fluorescence properties, an orthogonal design was applied to investigate these effects. Results show that HTC temperature and feedstock type are two key factors due to the diverse hydrolysis behaviors of components. A temperature of 190 °C effectively balances fluorescence clusters' generation and consumption, and the softwood, Pinus sylvestris var. mongolic, with its high hemicellulose and G-type lignin content, is an ideal feedstock. During HTC, LCDs are formed with a carbon core of conjugated cyclic structures from cross-linked, polymerized, and carbonized carbocyclic compounds, and a shell of polymer clusters from aliphatic hydrolysates. Here, hemicellulose and amorphous cellulose contribute to aliphatic and carbocyclic compounds, imparting hydrophilicity and fluorescence, while lignin supplies carbocyclic compounds essential for fluorescent carbon cores. As conjugation increased, the maximum fluorescence quantum yield (FQY) of LCDs reached 3.4 %. This work offers a theoretical basis for feedstock selection and explains the temporal formation process of LCDs, which is of great significance for the high-value utilization of lignocellulosic biomass and the regulation of LCDs' structures and optical properties.

Lignin-based biochar with improved properties derived from the microbial combined chemical pretreatment of corn straw for efficient antibiotic removal

In this study, straw lignin was separated from corn straw by combining microbial treatment with ρ-TsOH organic acid extraction for the first time, and lignin-derived biochars were prepared by carbonation-activation. The results showed that the extraction rate of lignin and the physicochemical properties of related biochars were improved greatly by microbial treatment. The specific surface areas of lignin biochar obtained after combined pre-treatment with Aspergillus niger, Myrothecium verrucaria, and Trichoderma reesei, (BNL, BML, and BTL) were 2348, 2849 and 3008 m2 g-1, respectively, and the total pore volumes were 0.8989, 0.9411, and 1.2621 cm3 g-1, which were significantly higher than the 2292 m2 g-1 and 0.7786 cm3 g-1 of the control group BCL (biochar prepared from lignin extracted from raw straw). In adsorption experiments by using tetracycline hydrochloride and sodium sulfadiazine as antibiotic models, the maximum adsorption capacities of all lignin-derived biochars (BML, BTL, and BNL) were greater than that of most other adsorbents including BCL. We hope this work could provide a new strategy for efficiently using microbial treatment technology to improve the conversion of lignocellulosic resources.

Exploration of high-value pathways for lignin: From catalyst preparation to product development

Considering the facts of fossil fuel depletion and environmental issues, the conversion of biomass into high value-added chemicals is of great importance. In this work, Ni and Co were encapsulated in lignin-derived phenolic resin spheres to obtain NiCo@LRS, which was then employed as a sacrificial template for the synthesis of the bimetallic catalyst NiCo@LC-RS. The Ni and Co act as the acid and dehydrogenation sites for the catalytic transfer hydrogenolysis of 2-phenoxy-1-phenylethanol (pp-ol) and corncob lignin, respectively, and exhibit a synergistic enhancement effect. Under the optimal conditions of 170 °C, 1 MPa N2 and 4 h, the conversion of pp-ol reached 99.9 %, with the yields of cyclohexanol and ethylbenzene at 99.9 % and 93.8 %, respectively. The lignin was completely converted and the selectivity of monophenols was 55.74 %. The catalyst remained stable and reusable after 5 cycles. Furthermore, lignin oil can be employed in the preparation of NiCo bimetallic catalysts, which have been demonstrated to exhibit excellent catalytic properties. This work provides practical guidance for the high-value utilisation of lignin.

A distinct autofluorescence distribution pattern marks enzymatic deconstruction of plant cell wall

Achieving an economically viable transformation of plant cell walls into bioproducts requires a comprehensive understanding of enzymatic deconstruction. Microscale quantitative analysis offers a relevant approach to enhance our understanding of cell wall hydrolysis, but becomes challenging under high deconstruction conditions. This study comprehensively addresses the challenges of quantifying the impact of extensive enzymatic deconstruction on plant cell wall at microscale. Investigation of highly deconstructed spruce wood provided spatial profiles of cell walls during hydrolysis with remarkable precision. A distinct cell wall autofluorescence distribution pattern marking enzymatic hydrolysis along with an asynchronous impact of hydrolysis on cell wall structure, with cell wall volume reduction preceding cell wall accessible surface area decrease, were revealed. This study provides novel insights into enzymatic deconstruction of cell wall at under-investigated cell scale, and a robust computational pipeline applicable to diverse biomass species and pretreatment types for assessing hydrolysis impact and efficiency.

Transcriptome response of the white-rot fungus Trametes versicolor to hybrid poplar exhibiting unique lignin chemistry

BACKGROUND

Production of biofuels and bioproducts from lignocellulosic material is limited due to the complexity of the cell wall structure. This necessitates the use of physical, chemical, and/or physico-chemical pretreatment technologies, which adds significant capital, operational, and environmental costs. Biological pretreatment strategies have the potential to mitigate these expenses by harnessing the innate ability of specialized bacteria and fungi to deconstruct lignocellulose. White-rot fungi (e.g. Trametes versicolor) have been shown to be effective at biological pretreatment of lignocellulose, yet it was uncertain if these fungi are feedstock agnostic or are able to sense subtle changes in cell wall chemistry.

RESULTS

The present study examined the transcriptome response by Trametes versicolor to transgenic hybrid poplar (Populus tremula × alba) lines with altered syringyl (S) and guaiacyl (G) lignin. Specifically, the transcriptional response of the fungus to wild-type wood was compared to that from the wood of six transgenic lines within three lignin phenotypes, LSX (low S with hydroxy-G), LSHG (low S with high G), and HS (high S), with 350 transcripts showing significant differences among the samples. The transcriptome of T. versicolor varied according to the lignin phenotype of the wood, with the LSX wood resulting in the most substantial changes in T. versicolor transcript abundance. Specifically, the LSX wood led to 50 upregulated and 48 downregulated transcripts from WT at the twofold or greater threshold. For example, transcripts for the lignin peroxidases LiP3 and LiP10 were downregulated (approximately 12X and 31X lower, respectively) by the fungus on LSX wood compared to wild-type wood. LSX wood also resulted in approximately 11X lower transcript numbers of endo-β-1,4-glucanase yet led to an increase in expression of certain hemicellulases, further highlighting the altered deconstruction strategy by the fungus on this wood type.

CONCLUSIONS

Overall, the results of this study demonstrated that T. versicolor was able to respond to transgenic poplar wood with the same genetic background, which has important implications for biological pretreatment strategies involving feedstocks that are genetically modified or have considerable natural variations in cell wall chemistry.

Effective pretreatment of tea stem via poly-deep eutectic solvent for promoting platform molecule production and obtaining fluorescent lignin

In this study, polyethylene glycol 200 (PEG200) was employed as hydrogen bond acceptor, while organic acids served as hydrogen bond donors, to formulate poly-deep eutectic solvents (PDESs), which were utilized to pretreat tea stem. Specially, combining PEG200 and oxalic acid (OA) exhibited a notably high cellulose retention (82.03 %) and most efficient hemicellulose (97.02 %) and lignin removal (70.89 %). The removal of amorphous lignin enhanced the crystallinity of the residues and improved the conversion efficiency of cellulose into levulinic acid. Additionally, the structural alterations in lignin samples were analyzed in comparison to milled wood lignin (MWL). The PEG200-OA system facilitated the cleavage of β-O-4 and β-5 linkages and resulted in the degradation of S-type lignin, accompanied by increased condensation of G units. The resulting lignin displayed a reduced molecular weight (Mw of 1283 g/mol, Mn value 531 g/mol) and nanoscale particle size (D50 212 nm). Furthermore, fluorescent lignin was synthesized through simple oxidation and was used to detect metal ions. Density functional theory (DFT) calculations supported that both PEG200 and OA played a significant role in lignin dissolution, with the weak interactions between DES and lignin primarily driven by hydrogen bonding (characterized as weak, closed-shell, and electrostatic) and van der Waals forces.

Construction of UCST-Responsive Claw-Like Polysulfobetaines for Efficient Capture of Cellulase

The high cost of enzymatic glycolysis has seriously restricted the industrialization of lignocellulose-based sugar platform technology. Recovering and recycling cellulase can reduce the cost. Here, a thermo-responsive claw-type polysulfobetaine (PSPA) was constructed for hydrophobic grasping and efficient recycling of cellulase. Compared with the linear sulfobetaine homopolymer (PSPE), PSPA had more sensitive temperature response and strong cellulase recovery ability. PSPE-3 (Mw=355.1 kDa) was added to the hydrolysis system of corncob residue (CCR) (50 °C), at 0.4 mass ratio of PSPE-3 to cellulase, and after enzymatic hydrolysis, 50 % of the cellulase was saved when cooling to 25 °C. But only 0.05 times PSPA-1 (Mw=30.0 kDa) was added to the CCR system, and 70 % of the cellulase was saved when cooling to 25 °C. This work presents a claw shaped protein-capture agent, polysulfobetaine for capturing cellulase, which is of great significance to reduce the lignocellulosic hydrolysis cost, and efficiently separate enzyme proteins.

A functional cascading of lignin modification via repression of caffeic acid O-methyltransferase for bioproduction and anti-oxidation in rice

INTRODUCTION

Crop straws provide substantial biomass resources that are transformable for sustainable biofuels and valuable bioproducts. However, the natural lignocellulose recalcitrance results in an expensive biomass process and secondary waste liberation. As lignin is a major recalcitrant factor, genetic engineering of lignin biosynthesis is increasingly being implemented in bioenergy crops, but much remains unclear about the desired lignocellulose alteration and resulting function.

OBJECTIVES

This study attempted to explore the mechanisms of lignin modification responsible for efficient lignocellulose conversion in vitro and an effective plant anti-oxidation response in vivo.

METHODS

We initially selected specific rice mutants by performing modern CRISPR/cas9 editing with caffeic acid O-methyltransferase involved in the synthetic pathways of monolignols (G, S) and ferulic acid (FA), and then explored lignocellulose conversion and plant cadmium (Cd) accumulation using advanced chemical, biochemical and thermal-chemical analyses.

RESULTS

Notable lignin modification was achieved from the predominately synergistic down-regulation of S-monomer synthesis in three mutants. This consequently upgraded lignocellulose porosity by up to 1.8 folds to account for significantly enhanced biomass saccharification and bioethanol production by 20 %-26 % relative to the wild-type. The modified lignin also favors the dissection of diverse lignin nanoparticles with dimensions reduced by 1.5-1.9 folds, applicable for thermal-chemical conversion into the carbon quantum dots with increased yields by 15 % and 31 %. The proportions of G-monomers and FA were significantly increased in the mutants, and the lignin extractions were further assayed with higher activities for two standard antioxidants (DPPH and ABTS) in vitro compared to the wild-type, revealing a distinctively enhanced plant antioxidative capacity in the mutants. Water culture showed that young mutant seedlings accumulated more Cd than wild-type did (p < 0.01, n = 3), suggesting effective heavy metal phytoremediation in the mutants.

CONCLUSION

A hypothetical model of characteristic lignin modification for specific S-monomer reduction, accountable for improved lignocellulose recalcitrance, was proposed. It provides a powerful strategy for achieving high-yield biofuels and value-added bioproducts or enhancing plant antioxidative capacity for heavy metal phytoremediation.

Simultaneous enhancement of activity and stability of Bacillus safensis-derived laccase and its application in lignocellulose saccharification

Effective hydrolysis of lignocelluloses for producing reducing sugar is impeded by the covalent binding of hemicellulose and cellulose through lignin, which could be eliminated by laccases. This study identified a novel thermostable laccase from Bacillus safensis TCCC 111022 and created an iterative mutant E231D/Y441H, exhibiting 1.59-fold greater specific activity and a 183 % greater half-life at 80°C than the wild-type enzyme. Computational analysis revealed that the stability and activity of the E231D/Y441H could be simultaneously enhanced by increasing the flexibility of the ring around the substrate binding pocket. Additionally, the saccharification efficiency of sugarcane bagasse and corn stalks were both enhanced by 235 % in the system adding E231D/Y441H, mixed-cellulases, and mediator (1-hydroxybenzotriazole) compared to the samples treated with mixed-cellulases. The findings of this research provide a reference for the degradation of lignocellulosic substrates and contribute to the sustainable development of biomass-based industries.

Ultra-high-pressure homogenization combined with ionic liquid-organic acid solvent for effective pretreatment of lignocellulose biomass

The complex structure of lignocellulose necessitates advanced pretreatment techniques to effectively separate its three primary components for further conversion into valuable products. This study introduced an innovative approach to pretreating bagasse by commencing with ultra-high-pressure homogenization (UHPH) applied to raw bagasse, which maintained chemical integrity while reducing intermolecular bonds, crystallinity, and particle size. Subsequently, UHPH-bagasse underwent pretreatment using a synergistic solution of ionic liquid ([Bmim]Cl) and organic acid (oxalic acid: OA). This combination achieved a remarkable 90.26 % lignin removal rate, surpassing many conventional methods. The influence of temperature on pretreatment efficiency was also explored, demonstrating effective lignin removal at temperatures below 130 °C without compromising cellulose integrity. This performance greatly enhanced cellulose conversion into levulinic acid (from 38.8 % to 57.5). However, temperatures exceeding 140 °C led to lignin depolymerization and subsequent re-aggregation on the residue's surface, hindering cellulose conversion. The [Bmim]Cl-OA system not only aided bagasse delignification but also promoted cleavage of β-O-4' linkages, especially at higher temperatures. The resulting lignin exhibited reduced molecular weight and nanoscale particle size, enhancing its antioxidant properties and suggesting potential applications in lignin-based chemicals and materials.

The role of NMR spectroscopy in lignocellulosic biomass characterisation: A mini review

Lignocellulosic biomass (LB) is promising feedstock for the production of various bio-based products. However, due to its heterogenous character, complex chemical structure and recalcitrance, it is necessary to know its structural composition in order to optimize pretreatment process and further (bio)conversion into bio-based products. Nuclear Magnetic Resonance (NMR) spectroscopy is a fast and reliable method that can provide advanced data on the molecular architecture and composition of lignocellulosic biomass. In this brief overview, characteristic examples of the use of high-resolution NMR spectroscopy for the investigation of various types of LB and their structural units are given and the main drawbacks and future perspectives are outlined.

Plant cell wall enzymatic deconstruction: Bridging the gap between micro and nano scales

Understanding lignocellulosic biomass resistance to enzymatic deconstruction is crucial for its sustainable conversion into bioproducts. Despite scientific advances, quantitative morphological analysis of plant deconstruction at cell and tissue scales remains under-explored. In this study, an original pipeline is devised, involving four-dimensional (space  + time) fluorescence confocal imaging, and a novel computational tool, to track and quantify deconstruction at cell and tissue scales. By applying this pipeline to poplar wood, dynamics of cellular parameters was computed and cellulose conversion during enzymatic deconstruction was measured. Results showed that enzymatic deconstruction predominantly impacts cell wall volume rather than surface area. Additionally, a negative correlation was observed between pre-hydrolysis compactness measures and volumetric cell wall deconstruction rate, whose strength was modulated by enzymatic activity. Results also revealed a strong positive correlation between average volumetric cell wall deconstruction rate and cellulose conversion rate. These findings link key deconstruction parameters across nano and micro scales.

Biotechnological approaches for producing natural pigments in yeasts

Pigments are widely used in the food, cosmetic, textile, pharmaceutical, and materials industries. Demand for natural pigments has been increasing due to concerns regarding potential health problems and environmental pollution from synthetic pigments. Microbial production of natural pigments is a promising alternative to chemical synthesis or extraction from natural sources. Here, we discuss yeasts as promising chassis for producing natural pigments with their advantageous traits such as genetic amenability, safety, rapid growth, metabolic diversity, and tolerance. Metabolic engineering strategies and optimizing strategies in downstream process to enhance production of natural pigments are thoroughly reviewed. We discuss the challenges, including expanding the range of natural pigments and improving their feasibility of industrial scale-up, as well as the potential strategies for future development.

Cell wall remodeling confers plant architecture with distinct wall structure in Nelumbo nucifera

Lotus (Nelumbo nucifera G.) is a perennial aquatic horticultural plant with diverse architectures. Distinct plant architecture (PA) has certain attractive and practical qualities, but its genetic morphogenesis in lotus remains elusive. In this study, we employ genome-wide association analysis (GWAS) for the seven traits of petiole length (PLL), leaf length (LL), leaf width (LW), peduncle length (PLF), flower diameter (FD), petal length (PeL), and petal width (PeW) in 301 lotus accessions. A total of 90 loci are identified to associate with these traits across 4 years of trials. Meanwhile, we perform RNA sequencing (RNA-seq) to analyze the differential expression of the gene (DEG) transcripts between large and small PA (LPA and SPA) of lotus stems (peduncles and petioles). As a result, eight key candidate genes are identified that are all primarily involved in plant cell wall remodeling significantly associated with PA traits by integrating the results of DEGs and GWAS. To verify this result, we compare the cell wall compositions and structures of LPA versus SPA in representative lotus germplasms. Intriguingly, compared with the SPA lotus, the LPA varieties have higher content of cellulose and hemicellulose, but less filling substrates of pectin and lignin. Additionally, we verified longer cellulose chains and higher cellulose crystallinity with less interference in LPA varieties. Taken together, our study illustrates how plant cell wall remodeling affects PA in lotus, shedding light on the genetic architecture of this significant ornamental trait and offering a priceless genetic resource for future genomic-enabled breeding.

Upgraded cellulose and xylan digestions for synergistic enhancements of biomass enzymatic saccharification and bioethanol conversion using engineered Trichoderma reesei strains overproducing mushroom LeGH7 enzyme

Crop straws provide enormous lignocellulose resources transformable for sustainable biofuels and valuable bioproducts. However, lignocellulose recalcitrance basically restricts essential biomass enzymatic saccharification at large scale. In this study, the mushroom-derived cellobiohydrolase (LeGH7) was introduced into Trichoderma reesei (Rut-C30) to generate two desirable strains, namely GH7-5 and GH7-6. Compared to the Rut-C30 strain, both engineered strains exhibited significantly enhanced enzymatic activities, with β-glucosidases, endocellulases, cellobiohydrolases, and xylanase activities increasing by 113 %, 140 %, 241 %, and 196 %, respectively. By performing steam explosion and mild alkali pretreatments with mature straws of five bioenergy crops, diverse lignocellulose substrates were effectively digested by the crude enzymes secreted from the engineered strains, leading to the high-yield hexoses released for bioethanol production. Notably, the LeGH7 enzyme purified from engineered strain enabled to act as multiple cellulases and xylanase at higher activities, interpreting how synergistic enhancement of enzymatic saccharification was achieved for distinct lignocellulose substrates in major bioenergy crops. Therefore, this study has identified a novel enzyme that is active for simultaneous hydrolyses of cellulose and xylan, providing an applicable strategy for high biomass enzymatic saccharification and bioethanol conversion in bioenergy crops.

Tobacco as bioenergy and medical plant for biofuels and bioproduction

Tobacco, a widely cultivated crop, has been extensively utilized by humans for an extended period. However, the tobacco industry generates a significant amount of organic waste, and the effective utilization of this tobacco waste has been limited. Currently, most tobacco waste is either recycled as reconstituted tobacco sheets or disposed of in landfills. However, tobacco possesses far more potential value than just these applications. This article provides an overview of the diverse uses of tobacco waste in agriculture, medicine, chemical engineering, and energy sectors. In the realm of agriculture, tobacco waste finds primary application as fertilizers and pesticides. In medical applications, the bioactive compounds present in tobacco are fully harnessed, resulting in the production of phenols, solanesol, polysaccharides, proteins, and even alkaloids. These bioactive compounds exhibit beneficial effects on human health. Additionally, the applications of tobacco waste in chemical engineering and energy sectors are centered around the utilization of lignocellulosic compounds and certain fuels. Chemical platform compounds derived from tobacco waste, as well as selected fuel sources, play a significant role in these areas. The rational utilization of tobacco waste represents a promising prospect, particularly in the present era when sustainable development is widely advocated. Moreover, this approach holds significant importance for enhancing energy utilization.

The outlooks and key challenges in renewable biomass feedstock utilization for value-added platform chemical via bioprocesses

The conversion of renewable biomass feedstock into value-added products via bioprocessing platforms has become attractive because of environmental and health concerns. Process performance and cost competitiveness are major factors in the bioprocess design to produce desirable products from biomass feedstock. Proper pretreatment allows delignification and hemicellulose removal from the liquid fraction, allowing cellulose to be readily hydrolyzed to monomeric sugars. Several industrial products are produced via sugar fermentation using either naturally isolated or genetically modified microbes. Microbial platforms play an important role in the synthesis of several products, including drop-in chemicals, as-in products, and novel compounds. The key elements in developing a fermentation platform are medium formulation, sterilization, and active cells for inoculation. Downstream bioproduct recovery may seem like a straightforward chemical process, but is more complex, wherein cost competitiveness versus recovery performance becomes a challenge. This review summarizes the prospects for utilizing renewable biomass for bioprocessing.

Bioethanol Production from Characterized Pre-treated Sugarcane Trash and Jatropha Agrowastes

Low production costs and a potential feedstock supply make lignocellulosic ethanol (bioethanol) an important source of advanced biofuels. The physical and chemical preparation of this kind of lignocellulosic feedstock led to a high ethanol yield. In order to increase the yield of fermentable sugars, pretreatment is an essential process step that alters the lignocellulosic structure and improves its accessibility for the expensive hydrolytic enzymes. In this context, the chemical composition of sugarcane trash (dry leaves, green leaves, and tops) and jatropha (shell and seed cake) was determined to be mainly cellulose, hemicellulose, and lignin. Hydrogen peroxide and sodium hydroxide were applied in an attempt to facilitate the solubilization of lignin and hemicelluloses in five agrowastes. The extraction of hydrogen peroxide was much better than that of sodium hydroxide. A comparative study was done using SEM, EDXA, and FTIR to evaluate the difference between the two methods. The pretreated wastes were subjected to saccharification by commercial cellulases (30 IU/g substrate). The obtained glucose was fortified with nutrients and fermented statically by Saccharomyces cerevisiae F-307 for bioethanol production. The results revealed the bioethanol yields were 325.4, 310.8, 282.9, 302.4 and 264.0 mg ethanol/g treated agrowastes from green leaves of sugarcane, jatropha deolied seed cake, tops sugarcane, dry leaves of sugarcane, and jatropha shell, respectively. This study emphasizes the value of lignocellulosic agricultural waste as a resource for the production of biofuels as well as the significance of the extraction process.

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Side chain of confined xylan affects cellulose integrity leading to bending stem with reduced mechanical strength in ornamental plants

The stem support for fresh-cut flowers exerts a profound influence on the display of their blossoms. During vase insertion, bending stems significantly affect the ornamental value, but much remains unclear about the underlying reasons. In this study, six pairs of ornamental plants were screened for the contrast of bending and straight stems. The bending stems have weakened mechanical force and biomass recalcitrance compared with the straight ones. Meanwhile, cells in the bending stems became more loosely packed, along with a decrease in cell wall thickness and cellulose levels. Furthermore, wall properties characterizations show bending stems have decreased lignocellulosic CrI and cellulose DP, and enhanced the branching ratio of hemicellulose which is trapped in the cellulose. Given the distinct cell wall factors in different species, all data are grouped in standardized to eliminate the variations among plant species. The principal composition analysis and correlation analysis of the processed dataset strongly suggest that cellulose association factors determine the stem mechanical force and recalcitrance. Based on our results, we propose a model for how branches of confined hemicellulose interacted with cellulose to modulate stem strength support for the straight or bending phenotype in cut flowers.

Exploring the relationships between human consumption and environmental pressure: A case study of the Yangtze river economic zone in China

It is crucial to decouple and coordinate human consumption and its environmental pressure for achieving sustainable development. As an important aspect of United Nations Sustainable Development Goal (SDG12), sustainability on material consuming is still in its early stages of research. To address the research gap in sustainable consumption of vegetation net primary productivity (NPP), this study analyzed the spatio-temporal dynamics of human consumption and environmental pressure in the Yangtze River Economic Zone (YREZ) using consumption-based HANPP (cHANPP) and Human Appropriation of Net Primary Production (HANPP) as indicators. Later, we measured their decoupling relationship using Tapio decoupling approach. We found that distribution of HANPP and cHANPP were regionally separated, with the former mainly concentrated in the middle and upper reaches provinces, while the latter concentrated in the lower reach provinces. From 2004 to 2019, the relationship between HANPP and cHANPP changed from strong negative decoupling to weak decoupling in the YREZ. Furthermore, the relationship was differed among different regions. As a whole, developing regions showed a weak decoupling state, experiencing an increase in environmental pressure (i.e., HANPP) alongside increased human consumption (i.e., cHANPP). In contrast, developed regions showed a strong decoupling state, experiencing a decrease in environmental pressure (i.e., HANPP) alongside increased human consumption (i.e., cHANPP). Our study highlights that different countermeasures should be formulated by regions according to their own situation to realize sustainable regional development.

Efficient hemicellulose removal from lignocellulose by induced electric field-aided dilute acid pretreatment

This study evaluated the effectiveness of induced electric field (IEF) as a novel electrotechnology to assist dilute acid pretreatment of wheat straw (WS) at atmospheric pressure and low temperature (90 °C). The effects of acid concentration and duration on cellulose recovery, hemicellulose and lignin removal were investigated. Meanwhile, the differences between IEF pretreatment and hydrothermal pretreatment were compared by quantitative and qualitative analysis. The optimal pretreatment condition was acid concentration 1 % with the period of 5 h. Under the parameters, the hemicellulose removal of WS after IEF pretreatment was up to 73.6 %, and the enzymatic efficiency was 55.8 %. In addition, the irregular surface morphology, diminished functional groups associated with hemicellulose, increased specific surface area and pore volume, as well as improved thermal stability of the residual WS support the remarkable effect of IEF pretreatment. The feasibility of IEF pretreatment is might be due to the fact that the magneto-induced electric field promotes ionization of H+ and formation of hydrated hydrogen ions, increasing the acidity of the medium. Secondly, electroporation disrupts the anti-degradation structure of WS and increases the accessibility of cellulose to cellulases. It indicated that IEF is a green and efficient strategy for assisting the separation of hemicellulose from lignocellulose.

Lignin reduction in sugarcane by performing CRISPR/Cas9 site-direct mutation of SoLIM transcription factor

Genetic engineering of plant cell walls is limited for reducing lignocellulose recalcitrance, so mild and/or green-like pretreatment is still required for sequential enzymatic saccharification. Here, we report a method to reduce lignin content in sugarcane stalks using the CRISPR/Cas 9 technique. Three target sequences of SoLIM were designed and fused to pRGEB32. The cassette constructs were introduced into sugarcane calli cv. KK3 through Agrobacterium-mediated transformation. We produced one base substitution and one insertion line for the 1st target site; two insertions, one deletion, and one base substitution for the 2nd target site; and one base substitution and insertion for the 3rd target site. qRT-PCR analysis of SoLIM, SoPAL, SoC4H, and SoCAD showeded that downregulation of SoLIM by single nucleotide insertions or deletions reduced the expression of SoPAL, SoC4H, and SoCAD. Consequently, the edited lines contained 9.74 to 51.46% less lignin content compared to that in the wild-type plants. The syringyl/guaiacyl (S/G) ratio of the edited lines ranged between 0.23 and 0.49, while the wild-type was 0.22. The histochemical evaluation and scanning electron microscopy of the cell walls supported this observation. A low lignin content sugarcane will provide a better feedstock for second-generation bioethanol production.

Bioconversion of volatile fatty acids from organic wastes to produce high-value products by photosynthetic bacteria: A review

Anaerobic fermentation of organic waste to produce volatile fatty acids (VFAs) production is a relatively mature technology. VFAs can be used as a cheap and readily available carbon source by photosynthetic bacteria (PSB) to produce high value-added products, which are widely used in various applications. To better enhance the VFAs obtained from organic wastes for PSB to produce high value-added products, a comprehensive review is needed, which is currently not available. This review systematically summarizes the current status of microbial proteins, H2, poly-β-hydroxybutyrate (PHB), coenzyme Q10 (CoQ10), and 5-aminolevulinic acid (ALA) production by PSB utilizing VFAs as a carbon resource. Meanwhile, the metabolic pathways involved in the H2, PHB, CoQ10, and 5-ALA production by PSB were deeply explored. In addition, a systematic resource utilization pathway for PSB utilizing VFAs from anaerobic fermentation of organic wastes to produce high value-added products was proposed. Finally, the current challenges and priorities for future research were presented, such as the screening of efficient PSB strains, conducting large-scale experiments, high-value product separation, recovery, and purification, and the mining of metabolic pathways for the VFA utilization to generate high value-added products by PSB.

Metabolic engineering of Paenibacillus polymyxa for effective production of 2,3-butanediol from poplar hydrolysate

2,3-Butanediol is an essential renewable fuel. The synthesis of 2,3-butanediol using Paenibacillus polymyxa has attracted increasing attention. In this study, the glucose-derived 2,3-butanediol pathway and its related genes were identified in P. polymyxa using combined transcriptome and metabolome analyses. The functions of two distinct genes ldh1 and ldh3 encoding lactate dehydrogenase, the gene bdh encoding butanediol dehydrogenase, and the spore-forming genes spo0A and spoIIE were studied and directly knocked out or overexpressed in the genome sequence to improve the production of 2,3-butanediol. A raw hydrolysate of poplar wood containing 27 g/L glucose and 15 g/L xylose was used to produce 2,3-butanediol with a maximum yield of 0.465 g/g and 93 % of the maximum theoretical value, and the total production of 2,3-butanediol and ethanol reached 21.7 g/L. This study provides a new scheme for engineered P. polymyxa to produce renewable fuels using raw poplar wood hydrolysates.

Biochemical characterisation of cellulose and cell-wall-matrix polysaccharides in variously oxidised sugar-beet pulp preparations differing in viscosity

Sugar-beet pulp (SBP) is an abundant, cellulose-rich, non-food by-product of agriculture. Oxidised SBP (oP) has valuable viscosity attributes, and different oxidation protocols yield higher- or lower-viscosity oP. We investigated how SBP polysaccharides change during oxidation, since these changes must define oP quality. Oxidation solubilised much pectin and hemicellulose; however, most cellulose stayed insoluble. Fresh SBP contains negligible 'hemicellulose a' (=alkali-extractable polysaccharides that precipitate upon acidification), but oxidation created abundant glucose-rich 'hemicellulose a' from SBP cellulose. We propose that the cellulose acquired COOH groups, conferring alkali-extractability and admitting more water, thereby augmenting viscosity. The pectin and hemicellulose molecules that were retained during oxidation had been partially depolymerised, and their median Mr correlated negatively with oP viscosity. We developed a novel procedure to explore cellulose's permeability by measuring the ingress of tritium from [3H]water into microfibrils and its retention during desiccation. In high-crystallinity Avicel, 75 % of the cellulose's OH groups were inaccessible to [3H]water, whereas filter-paper cellulose acquired the theoretical maximum 3H, indicating an open structure. Retention of 3H by oP preparations correlated positively with viscosity, indicating that increased cellulose accessibility generates a viscous oP. In conclusion, depolymerisation and solubilisation of matrix polysaccharides, accompanied by increasing water-accessibility of cellulose, enhanced SBP's viscosity.

H2SO4 assisted hydrothermal conversion of biomass with solid acid catalysis to produce aviation fuel precursors

With hydrothermal reaction, lignocellulosic biomass can be efficiently converted into furfural (FF) and levulinic acid (LA), both of which are key platform compounds that can be used for the subsequent preparation of aviation fuels. In order to reduce the acid concentration in traditional hydrolysis and provide a reaction system with good catalytic activity, we propose a biomass conversion route as dilute acid hydrolysis coupled with solid acid catalysis. Firstly, at different temperatures, the hemicellulose and cellulose in corn stover were step-hydrolyzed by sulfuric acid solution with a concentration of 0.9 wt. % to produce xylose and glucose, with conversion reaching 100% and 97.3%, respectively. Subsequently, a new resin-derived carbon-based solid acid catalyst was used to catalyze the aforementioned saccharide solutions to obtain FF with yield of 68.7 mol % and LA of 70.3 mol %, respectively. This work provides a promising approach for the efficient production of bio-aviation fuel precursors.

Employing deep eutectic solvent synthesized by cetyltrimethylammonium bromide and ethylene glycol to advance enzymatic hydrolysis efficiency of rape straw

An efficient deep eutectic solvent (DES) was synthesized by cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG) and employed to treat rape straw (RS) for advancing enzymatic saccharification in this work. By optimizing the pretreatment parameters, the results displayed that the novel DES was strongly selective towards removing lignin and xylan while preserving cellulose. Under optimum conditions with 1:6 of CTAB: EG in DES, 180 °C and 80 min, the enzymatic hydrolysis efficiency of RS was enhanced by 46.0% due to the 62.2% of delignification and 53.2% of xylan removal during CTAB: EG pretreatment. In terms of the recalcitrant structure of RS, DES pretreatment caused the increment of cellulosic accessibility, reduction of hydrophobicity and surface area of lignin, and migration of cellulosic crystalline structure, which was associated with its enzymatic hydrolysis efficiency. Overall, this study presented an emerging method for the effective fractionation and valorization of lignocellulosic biomass within biorefinery technology.

Efficient production of hydroxymethyl-2-furfurylamine by chemoenzymatic cascade catalysis of bread waste in a sustainable approach

In this study, efficient and sustainable conversion of waste bread (WB) to 5-hydroxymethyl-2-furoamine (HMFA) was achieved in a cascade reaction in betaine:malonic acid (B:MA) - water. 5-HMF (30.3 wt% yield) was synthesized from WB (40.0 g/L) in B:MA - water (B:MA, 18 wt%) in 45 min at 190 °C. By using the newly created recombinant E. coli HNILGD-AlaDH cells expressing L-alanine dehydrogenase (AlaDH) and ω-transaminase mutant HNILGD as biocatalyst, the WB-valorized 5-HMF was biologically aminated into HMFA in a high yield (92.1%) at 35 °C for 12 h through in situ removal of the amino transfer by-products of the amine donor, greatly reducing amine donor dosage (from D-Ala/5-HMF = 16/1 to D-Ala/5-HMF = 2/1, mol/mol) and improving the productivity of HMFA (0.282 g HMFA per g WB). This two-step chemical-enzymatic cascade reaction strategy with B:MA and HNILGD-AlaDH whole-cell provides a new idea for the chemoenzymatic synthesis of valuable furan chemicals from waste biomass.

Fungal strain improvement for efficient cellulase production and lignocellulosic biorefinery: Current status and future prospects

Lignocellulosic biomass (LCB) has been recognized as a valuable carbon source for the sustainable production of biofuels and value-added biochemicals. Crude enzymes produced by fungal cell factories benefit economic LCB degradation. However, high enzyme production cost remains a great challenge. Filamentous fungi have been widely used to produce cellulolytic enzymes. Metabolic engineering of fungi contributes to efficient cellulase production for LCB biorefinery. Here the latest progress in utilizing fungal cell factories for cellulase production was summarized, including developing genome engineering tools to improve the efficiency of fungal cell factories, manipulating promoters, and modulating transcription factors. Multi-omics analysis of fungi contributes to identifying novel genetic elements for enhancing cellulase production. Furthermore, the importance of translation regulation of cellulase production are emphasized. Efficient development of fungal cell factories based on integrative strain engineering would benefit the overall bioconversion efficacy of LCB for sustainable bioproduction.

Enhancing enzymatic saccharification of sunflower straw through optimal tartaric acid hydrothermal pretreatment

Sunflower straw, a usually neglected and abundant agricultural waste, has great potential for contributing to environmental protection realizing its high-value of valorization if utilizing properly. Because hemicellulose contains amorphous polysaccharide chains, relatively mild organic acid pretreatment can effectively reduce its resistance. Through hydrothermal pretreatment, sunflower straw was pretreated in tartaric acid (1 wt%) at 180 ^oC for 60 min to enhance its reducing sugar recovery. After tartaric acid-assisted hydrothermal pretreatment, 39.9% of lignin and 90.2% of hemicellulose were eliminated. The reducing sugar recovery increased threefold, while the solution could be effectively reused for four cycles. The properties of more porous surface, improved accessibility, and decreased surface lignin area of sunflower straw were observed through various characterizations, which explained the improved saccharide recovery and provided a basis for the mechanism of tartaric acid-assisted hydrothermal pretreatment. Overall, this tartaric acid hydrothermal pretreatment strategy greatly provided new impetus for the biomass refinery.

Selective saccharification of crude glycerol pretreated sugarcane bagasse via fast pyrolysis: reaction kinetics and life cycle assessment

Saccharification is a pivotal step in the conversion of lignocellulose to biofuels and chemicals. In this study, crude glycerol derived from biodiesel production was used in pretreatment to facilitate efficient and clean pyrolytic saccharification of sugarcane bagasse. Delignification, demineralization, destruction of lignin-carbohydrate complex structure, and cellulose crystallinity improvement in crude glycerol pretreated biomass could enhance levoglucosan producing reactions against competitive reactions, and therefore facilitate a kinetically controlled pyrolysis with apparent activation energy increased by 2-fold. Accordingly, selective levoglucosan production (44.4%) was promoted by 6-fold whilst light oxygenates and lignin monomers were limited to <25% in bio-oil. Owing to the high-efficiency saccharification, life cycle assessment suggested that the environmental impacts of the integrated process were less than those of typical acid pretreatment and petroleum-based processes, especially on the acidification (8-fold less) and global warming potential. This study provides an environmentally benign approach to efficient biorefinery and waste management.

Improved production of adipic acid from a high loading of corn stover via an efficient and mild combination pretreatment

Adipic acid is one kind of important organic dibasic acid, which has crucial role in manufacturing plastics, lubricants, resins, fibers, etc. Using lignocellulose as feedstock for producing adipic acid can reduce production cost and improve bioresource utilization. After pretreated in the mixture of 7 wt% NaOH and 8 wt% ChCl-PEG10000 at 25 ^oC for 10 min, the surface of corn stover became loose and rough. The specific surface area was increased after the removal of lignin. A high loading of pretreated corn stover was enzymatically hydrolyzed by cellulase (20 FPU/g substrate) and xylanase (15 U/g substrate), and the yield of reducing sugars was as high as 75%. Biomass-hydrolysates obtained by enzymatic hydrolysis were efficiently fermented to produce adipic acid, and the yield was 0.45 g adipic acid per g reducing sugar. A sustainable approach for manufacturing adipic acid from lignocellulose via a room temperature pretreatment has great potential in future.

BsEXLX of engineered Trichoderma reesei strain as dual-active expansin to boost cellulases secretion for synergistic enhancement of biomass enzymatic saccharification in corn and Miscanthus straws

In this study, bacterial BsEXLE1 gene was overexpressed into T. reesei (Rut-C30) to generate a desirable engineered TrEXLX10 strain. While incubated with alkali-pretreated Miscanthus straw as carbon source, the TrEXLX10 secreted the β-glucosidases, cellobiohydrolases and xylanses with activities raised by 34%, 82% and 159% compared to the Rut-C30. Supplying EXLX10-secreted crude enzymes and commercial mixed-cellulases for two-step lignocellulose hydrolyses of corn and Miscanthus straws after mild alkali pretreatments, this work measured consistently higher hexoses yields released by the EXLX10-secreted enzymes for synergistic enhancements of biomass saccharification in all parallel experiments examined. Meanwhile, this study detected that the expansin, purified from EXLX10-secreted solution, was of exceptionally high binding activities with wall polymers, and further determined its independent enhancement for cellulose hydrolysis. Therefore, this study raised a mechanism model to highlight EXLX/expansin dual-activation roles for both secretion of stable biomass-degradation enzymes at high activity and biomass enzymatic saccharification in bioenergy crops.