Biological pretreatment of lignocellulosic biomass--An overview

Genomic analysis of a halophilic bacterium Nesterenkonia sp. CL21 with ability to produce a diverse group of lignocellulolytic enzymes

Halophilic bacteria are extremophiles that thrive in saline environment. Their ability to withstand such harsh conditions makes them an ideal choice for industrial applications such as lignocellulosic biomass degradation. In this study, a halophilic bacterium with the ability to produce extracellular cellulases and hemicellulases, designated as Nesterenkonia sp. CL21, was isolated from mangrove sediment in Tanjung Piai National Park, Malaysia. Thus far, studies on lignocellulolytic enzymes concerning bacterial species under this genus are limited. To gain a comprehensive understanding of its lignocellulose-degrading potential, the whole genome was sequenced using the Illumina NovaSeq 6000 platform. The genome of strain CL21 was assembled into 25 contigs with 3,744,449 bp and a 69.74% GC content and was predicted to contain 3,348 coding genes. Based on taxonomy analysis, strain CL21 shares 73.8 to 82.0% average nucleotide identity with its neighbouring species, below the 95% threshold, indicating its possible status as a distinct species in Nesterenkonia genus. Through in-depth genomic mining, a total of 81 carbohydrate-active enzymes were encoded. Among these, 24 encoded genes were identified to encompass diverse cellulases (GH3), xylanases (GH10, GH11, GH43, GH51, GH127 and CE4), mannanases (GH38 and GH106) and pectinases (PL1, PL9, and PL11). The production of lignocellulolytic enzymes was tested in the presence of several substrates. This study revealed that strain CL21 can produce a diverse array of enzymes which are active at different time points. By combining experimental data with genomic information, the ability of strain CL21 to produce lignocellulolytic enzymes has been elucidated, with potential applications in biorefinery industry.

A review of nanotechnology in enzyme cascade to address challenges in pre-treating biomass

Nanotechnology has become a revolutionary technique for improving the preliminary treatment of lignocellulosic biomass in the production of biofuels. Traditional methods of pre-treatment have encountered difficulties in effectively degrading the intricate lignocellulosic composition, thereby impeding the conversion of biomass into fermentable sugars. Nanotechnology has enabled the development of enzyme cascade processes that present a potential solution for addressing the limitations. The focus of this review article is to delve into the utilization of nanotechnology in the pretreatment of lignocellulosic biomass through enzyme cascade processes. The review commences with an analysis of the composition and structure of lignocellulosic biomass, followed by a discussion on the drawbacks associated with conventional pre-treatment techniques. The subsequent analysis explores the importance of efficient pre-treatment methods in the context of biofuel production. We thoroughly investigate the utilization of nanotechnology in the pre-treatment of enzyme cascades across three distinct sections. Nanomaterials for enzyme immobilization, enhanced enzyme stability and activity through nanotechnology, and nanocarriers for controlled enzyme delivery. Moreover, the techniques used to analyse nanomaterials and the interactions between enzymes and nanomaterials are introduced. This review emphasizes the significance of comprehending the mechanisms underlying the synergy between nanotechnology and enzymes establishing sustainable and environmentally friendly nanotechnology applications.

Fungal behavior and recent developments in biopulping technology

Biological pretreatment of wood chips by fungi is a well-known approach prior to mechanical- or chemical pulp production. For this biological approach, a limited number of white-rot fungi with an ability to colonize and selectively degrade lignin are used to pretreat wood chips allowing the remaining cellulose to be processed for further applications. Biopulping is an environmentally friendly technology that can reduce the energy consumption of traditional pulping processes. Fungal pretreatment also reduces the pitch content in the wood chips and improves the pulp quality in terms of brightness, strength, and bleachability. The bleached biopulps are easier to refine compared to pulps produced by conventional methodology. In the last decades, biopulping has been scaled up with pilot trials towards industrial level, with optimization of several intermediate steps and improvement of economic feasibility. Nevertheless, fundamental knowledge on the biochemical mechanisms involved in biopulping is still lacking. Overall, biopulping technology has advanced rapidly during recent decades and pilot mill trials have been implemented. The use of fungi as pretreatment for pulp production is in line with modern circular economy strategies and can be implemented in existing production plants. In this review, we discuss some recent advances in biopulping technology, which can improve mechanical-, chemical-, and organosolv pulping processes along with their mechanisms.

Sustainable biorefinery approach by utilizing xylose fraction of lignocellulosic biomass

Lignocellulosic biomass (LCB) has been a lucrative feedstock for developing biochemical products due to its rich organic content, low carbon footprint and abundant accessibility. The recalcitrant nature of this feedstock is a foremost bottleneck. It needs suitable pretreatment techniques to achieve a high yield of sugar fractions such as glucose and xylose with low inhibitory components. Cellulosic sugars are commonly used for the bio-manufacturing process, and the xylose sugar, which is predominant in the hemicellulosic fraction, is rejected as most cell factories lack the five‑carbon metabolic pathways. In the present review, more emphasis was placed on the efficient pretreatment techniques developed for disintegrating LCB and enhancing xylose sugars. Further, the transformation of the xylose to value-added products through chemo-catalytic routes was highlighted. In addition, the review also recapitulates the sustainable production of biochemicals by native xylose assimilating microbes and engineering the metabolic pathway to ameliorate biomanufacturing using xylose as the sole carbon source. Overall, this review will give an edge on the bioprocessing of microbial metabolism for the efficient utilization of xylose in the LCB.

Optimizing cellulose fraction for enhanced utility: Comparative pre-treatment of Agave tequilana Weber var. blue bagasse fiber for sustainable applications

In recent decades, natural fibers have emerged as an alternative to synthetic fibers due to their renewable nature, lower environmental impact, and comparable strength properties. Agave bagasse, a byproduct of agave juice extraction in Mexico, stands out for its potential in various industrial applications, notably biocomposite production. Bagasse is rich in cellulose, along with hemicellulose and lignin. Cellulose is the most suitable to be converted into valuable products, and it is versatile, renewable, and biodegradable. An effective pre-treatment is crucial to enrich its fraction. This study aims to determine the optimal pre-treatment conditions for the agave bagasse. Three different pre-treatments were tested, acid (H2SO4), enzymatic (Cellic® HTec2 enzymatic preparation), and sequence of acid-enzymatic (sulfuric acid and Cellic® HTec2), to determine which pre-treatment got the optimal cellulose fraction increase. The acid pre-treatment was conducted over three time ranges (5, 10, and 15 min) at different acid concentrations (1%, 1.5%, and 2%). Enzymatic reactions were conducted over 24 h, testing three different enzyme concentrations (1.5%, 3%, 4.5%). The sequential pre-treatment utilized the optimal conditions derived from the acid experiments (1.5% H2SO4 for 10 min), followed by enzymatic reactions carried out over three different durations (6, 12, and 24 h). The findings revealed that a 1.5% acid concentration applied for 10 min was the most efficient pre-treatment method. This pre-treatment resulted in a 1.9-fold increase in the cellulose fraction while reducing hemicellulose content by 30%. The hemicellulose reduction was confirmed through Fourier Transform IR spectroscopy (FTIR) analysis, complemented by scanning electron microscopy (SEM) observations highlighting physical alterations in the fiber structure. Furthermore, thermogravimetric analysis (TGA) demonstrated improved thermal stability, suggesting potential use in biocomposites. Future research should evaluate the environmental impact of optimized pre-treatment methods for agave bagasse.

Valorization of crop residues and animal wastes: Anaerobic co-digestion technology

To switch the over-reliance on fossil-based resources, curb environmental quality deterioration, and promote the use of renewable fuels, much attention has recently been directed toward the implementation of sustainable and environmentally benign 'waste-to-energy' technology exploiting a clean, inexhaustible, carbon-neutral, and renewable energy source, namely agricultural biomass. From this perspective, anaerobic co-digestion (AcoD) technology emerges as a potent and plausible approach to attain sustainable energy development, foster environmental sustainability, and, most importantly, circumvent the key challenges associated with mono-digestion. This review article provides a comprehensive overview of AcoD as a biochemical valorization pathway of crop residues and livestock manure for biogas production. Furthermore, this manuscript aims to assess the different biotic and abiotic parameters affecting co-digestion efficiency and present recent advancements in pretreatment technologies designed to enhance feedstock biodegradability and conversion rate. It can be concluded that the substantial quantities of crop residues and animal waste generated annually from agricultural practices represent valuable bioenergy resources that can contribute to meeting global targets for affordable renewable energy. Nevertheless, extensive and multidisciplinary research is needed to evolve the industrial-scale implementation of AcoD technology of livestock waste and crop residues, particularly when a pretreatment phase is included, and bridge the gap between small-scale studies and real-world applications.

Sustainable utilization of fruit and vegetable waste bioresources for bioplastics production

Nowadays, rapidly increasing production, use and disposable of plastic products has become one of the utmost environmental issues. Our current circumstances in which the food supply chain is demonstrated as containing plastic particles and other plastic-based impurities, represents a significant health risk to humans, animals, and environmental alike. According to this point of view, biodegradable plastic material aims to produce a more sustainable and greener world with a lower ecological impact. Bioplastics are being investigated as an environmentally friendly candidate to address this problem and hence global bioplastic production has seen significant growth and expansion in recent years. This article focuses on a few critical issues that must be addressed for bioplastic production to become commercially viable. Although the reduction of fruit and vegetable waste biomass has an apparent value in terms of environmental benefits and sustainability, commercial success at industrial scale has remained flat. This is due to various factors, including biomass feedstocks, pretreatment technologies, enzymatic hydrolysis, and scale-up issues in the industry, all of which contribute to high capital and operating costs. This review paper summarizes the global overview of bioplastics derived from fruit and vegetable waste biomass. Furthermore, economic and technical challenges associated with industrialization and diverse applications of bioplastics in biomedical, agricultural, and food-packaging fields due to their excellent biocompatibility properties are reviewed.HighlightsReview of the diverse types and characteristics of sustainability of biobased plasticsImproved pretreatment technologies can develop to enhance greater yieldEnzyme hydrolysis process used for bioplastic extraction & hasten industrial scale-upFocus on technical challenges facing commercialized the bioplasticsDetailed discussion on the application for sustainability of biodegradable plastics.

Combination of alkaline biodiesel-derived crude glycerol pretreated corn stover with dilute acid pretreated water hyacinth for highly-efficient single cell oil production by oleaginous yeast Cutaneotrichosporon oleaginosum

Single cell oil (SCO) prepared from biodiesel-derived crude glycerol (BCG) and lignocellulosic biomass (LCB) via oleaginous yeasts is an intriguing alternative precursor of biodiesel. Here, a novel strategy combining alkaline BCG pretreated corn stover and dilute acid pretreated water hyacinth for SCO overproduction was developed. The mixed pretreatment liquors (MPLs) were naturally neutralized and adjusted to a proper carbon-to-nitrogen ratio beneficial for SCO overproduction by Cutaneotrichosporon oleaginosum. The toxicity of inhibitors was relieved by dilution detoxification. The enzymatic hydrolysate of solid fractions was suitable for SCO production either separately or simultaneously with MPLs. Fed-batch fermentation of the MPLs resulted in high cell mass, SCO content, and SCO titer of 80.7 g/L, 75.7 %, and 61.1 g/L, respectively. The fatty acid profiles of SCOs implied high-quality biodiesel characteristics. This study offers a novel BCG&LCB-to-SCO route integrating BCG-based pretreatment and BCG/LCB hydrolysates co-utilization, which provides a cost-effective technical route for micro-biodiesel production.

Utilization of coffee waste as a sustainable feedstock for high-yield lactic acid production through microbial fermentation

Lactic acid is an important industrial precursor; however, high substrate costs are a major challenge in microbial fermentation-based lactic acid production. Coffee waste is a sustainable feedstock alternative for lactic acid production via microbial fermentation. Herein, the feasibility of coffee waste as a feedstock was explored by employing appropriate pretreatment methods and optimizing enzyme combinations. Coffee waste pretreatment with hydrogen peroxide and acetic acid along with a combination of Viscozyme L, Celluclast 1.5 L, and Pectinex Ultra SP-L achieved the 78.9 % sugar conversion rate at a substrate concentration of 4 % (w/v). Lactiplantibacillus plantarum WiKim0126-induced fermentation with a 4 % solid loading yielded a lactic acid concentration of 22.8 g/L (99.6 % of the theoretical maximum yield) and productivity of 0.95 g/L/h within 24 h. These findings highlight the viability of coffee waste as an eco-friendly resource for sustainable lactic acid production.

Independent metabolism of oligosaccharides is the keystone of synchronous utilization of cellulose and hemicellulose in Myceliophthora

The effective utilization of cellulose and hemicellulose, the main components of plant biomass, is a key technical obstacle that needs to be overcome for the economic viability of lignocellulosic biorefineries. Here, we firstly demonstrated that the thermophilic cellulolytic fungus Myceliophthora thermophila can simultaneously utilize cellulose and hemicellulose, as evidenced by the independent uptake and intracellular metabolism of cellodextrin and xylodextrin. When plant biomass serviced as carbon source, we detected the cellodextrin and xylodextrin both in cells and in the culture medium, as well as high enzyme activities related to extracellular oligosaccharide formation and intracellular oligosaccharide hydrolysis. Sugar consumption assay revealed that in contrast to inhibitory effect of glucose on xylose and cellodextrin/xylodextrin consumption in mixed-carbon media, cellodextrin and xylodextrin were synchronously utilized in this fungus. Transcriptomic analysis also indicated simultaneous induction of the genes involved in cellodextrin and xylodextrin metabolic pathway, suggesting carbon catabolite repression (CCR) is triggered by extracellular glucose and can be eliminated by the intracellular hydrolysis and metabolism of oligosaccharides. The xylodextrin transporter MtCDT-2 was observed to preferentially transport xylobiose and tolerate high cellobiose concentrations, which helps to bypass the inhibition of xylobiose uptake. Furthermore, the expression of cellulase and hemicellulase genes was independently induced by their corresponding inducers, which enabled this strain to synchronously utilize cellulose and hemicellulose. Taken together, the data presented herein will further elucidate the degradation of plant biomass by fungi, with implications for the development of consolidated bioprocessing-based lignocellulosic biorefinery.

Enhancing biogas generation from lignocellulosic biomass through biological pretreatment: Exploring the role of ruminant microbes and anaerobic fungi

Biogas production from Lignocellulosic Biomass (LB) via anaerobic digestion (AD) has gained attention for its potential in self-sustainability. However, the recalcitrance of LB cell walls pose a challenge to its degradability and biogas generation. Therefore, pretreatment of LB is necessary to enhance lignin removal and increase degradability. Among the different approaches, environmentally friendly biological pretreatment ispromising as it avoids the production of inhibitors. The ruminal microbial community, including anaerobic fungi, bacteria, and protozoa, has shown an ability to effectively degrade LB through biomechanical and microbial penetration of refractory cell structures. In this review, we provide an overview of ruminant microbes dominating LB's AD, their degradation mechanism, and the bioaugmentation of the rumen. We also explore the potential cultivation of anaerobic fungi from the rumen, their enzyme potential, and their role in AD. The rumen ecosystem, comprising both bacteria and fungi, plays a crucial role in enhancing AD. This comprehensive review delves into the intricacies of ruminant microorganisms' adhesion to plant cells, elucidates degradation mechanisms, and explores integrated pretreatment approaches for the effective utilization of LB, minimizing the impact of inhibitors. The discussion underscores the considerable potential of ruminant microbes in pretreating LB, paving the way for sustainable biogas production. Optimizing fungal colonization and ligninolytic enzyme production, such as manganese peroxidase and laccase, significantly enhances the efficiency of fungal pretreatment. Integrating anaerobic fungi through bioaugmentation during mainstream processing demonstrably increases methane production. This study opens promising avenues for further research and development of these microorganisms for bioenergy production.

The production of ultrahigh molecular weight xanthan gum from a Sphingomonas chassis capable of co-utilising glucose and xylose from corn straw

Corn straw is an abundant and renewable alternative for microbial biopolymer production. In this paper, an engineered Sphingomonas sanxanigenens NXG-P916 capable of co-utilising glucose and xylose from corn straw total hydrolysate to produce xanthan gum was constructed. This strain was obtained by introducing the xanthan gum synthetic operon gum as a module into the genome of the constructed chassis strain NXdPE that could mass produce activated precursors of polysaccharide, and in which the transcriptional levels of gum genes were optimised by screening for a more appropriate promoter, P916 . As a result, strain NXG-P916 produced 9.48 ± 0.34 g of xanthan gum per kg of fermentation broth (g/kg) when glucose was used as a carbon source, which was 2.1 times improved over the original engineering strain NXdPE::gum. Furthermore, in batch fermentation, 12.72 ± 0.75 g/kg xanthan gum was produced from the corn straw total hydrolysate containing both glucose and xylose, and the producing xanthan gum showed an ultrahigh molecular weight (UHMW) of 6.04 × 107  Da, which was increased by 15.8 times. Therefore, the great potential of producing UHMW xanthan gum by Sphingomonas sanxanigenens was proved, and the chassis NXdPE has the prospect of becoming an attractive platform organism producing polysaccharides derived from biomass hydrolysates.

Exploring the potential of a new thermotolerant xylanase from Rasamsonia composticola (XylRc): production using agro-residues, biochemical studies, and application to sugarcane bagasse saccharification

Xylanases from thermophilic fungi have a wide range of commercial applications in the bioconversion of lignocellulosic materials and biobleaching in the pulp and paper industry. In this study, an endoxylanase from the thermophilic fungus Rasamsonia composticola (XylRc) was produced using waste wheat bran and pretreated sugarcane bagasse (PSB) in solid-state fermentation. The enzyme was purified, biochemically characterized, and used for the saccharification of sugarcane bagasse. XylRc was purified 30.6-fold with a 22% yield. The analysis using sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed a molecular weight of 53 kDa, with optimal temperature and pH values of 80 °C and 5.5, respectively. Thin-layer chromatography suggests that the enzyme is an endoxylanase and belongs to the glycoside hydrolase 10 family. The enzyme was stimulated by the presence of K+, Ca2+, Mg2+, and Co2+ and remained stable in the presence of the surfactant Triton X-100. XylRc was also stimulated by organic solvents butanol (113%), ethanol (175%), isopropanol (176%), and acetone (185%). The Km and Vmax values for oat spelt and birchwood xylan were 6.7 ± 0.7 mg/mL, 2.3 ± 0.59 mg/mL, 446.7 ± 12.7 µmol/min/mg, and 173.7 ± 6.5 µmol/min/mg, respectively. XylRc was unaffected by different phenolic compounds: ferulic, tannic, cinnamic, benzoic, and coumaric acids at concentrations of 2.5-10 mg/mL. The results of saccharification of PSB showed that supplementation of a commercial enzymatic cocktail (Cellic® CTec2) with XylRc (1:1 w/v) led to an increase in the degree of synergism (DS) in total reducing sugar (1.28) and glucose released (1.05) compared to the control (Cellic® HTec2). In summary, XylRc demonstrated significant potential for applications in lignocellulosic biomass hydrolysis, making it an attractive alternative for producing xylooligosaccharides and xylose, which can serve as precursors for biofuel production.

Lignin Extraction by Using Two-Step Fractionation: A Review

Lignocellulosic biomass represents the most abundant renewable carbon source on earth and is already used for energy and biofuel production. The pivotal step in the conversion process involving lignocellulosic biomass is pretreatment, which aims to disrupt the lignocellulose matrix. For effective pretreatment, a comprehensive understanding of the intricate structure of lignocellulose and its compositional properties during component disintegration and subsequent conversion is essential. The presence of lignin-carbohydrate complexes and covalent interactions between them within the lignocellulosic matrix confers a distinctively labile nature to hemicellulose. Meanwhile, the recalcitrant characteristics of lignin pose challenges in the fractionation process, particularly during delignification. Delignification is a critical step that directly impacts the purity of lignin and facilitates the breakdown of bonds involving lignin and lignin-carbohydrate complexes surrounding cellulose. This article discusses a two-step fractionation approach for efficient lignin extraction, providing viable paths for lignin-based valorization described in the literature. This approach allows for the creation of individual process streams for each component, tailored to extract their corresponding compounds.

Cheminformatics identification of modulators of key carbohydrate-metabolizing enzymes from C. cujete for type-2 diabetes mellitus intervention

Purpose

The therapeutic use of oral hypoglycaemic agents in the management of type-2 diabetes mellitus (T2DM) is without adverse effects; thus, calls for alternative and novel candidates from natural products in medicinal plants.

Method

The study explored molecular docking and molecular dynamics (MD) simulation approaches to identify key antidiabetic metabolites from Crescentia cujete.

Results

Molecular docking results identified four and/or five best compounds against each target enzyme (alpha-glucosidase, dipeptidyl peptidase-IV, aldose reductase, and protein tyrosine phosphatase-1B (PTP-1B)) implicated in diabetes. The resulting complexes (except against PTP-1B) had higher docking scores above respective standards (acarbose, Diprotin A, ranirestat). The MD simulation results revealed compounds such as benzoic acid (-48.414 kcal/mol) and phytol (-45.112 kcal/mol) as well as chlorogenic acid (-42.978 kcal/mol) and naringenin (-31.292 kcal/mol) had higher binding affinities than the standards [acarbose (-28.248 kcal/mol), ranirestat (-21.042 kcal/mol)] against alpha-glucosidase and aldose reductase, respectively while Diprotin A (-45.112 kcal/mol) and ursolic acid (-18.740 kcal/mol) presented superior binding affinities than the compounds [luteolin (-41.957 kcal/mol and naringenin (-16.518 kcal/mol)] against DPP-IV and PTP-1B respectively.

Conclusion

While isoflavone (alpha-glucosidase), xylocaine (DPP-IV), luteolin (aldose reductase,) and chlorogenic acid (PTP-1B) were affirmed as the best inhibitors of respective enzyme targets, luteolin, and chlorogenic acid may be suggested and proposed as probable candidates against T2DM and related retinopathy complication based on their structural stability, compactness and affinity for three (DPP-IV, aldose reductase, and PTP-1B) of the four targets investigated. Further studies are warranted in vitro and in vivo on the antihyperglycaemic effects of these drug candidates.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-023-01249-7.

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.

Sustainable biohydrogen production from lignocellulosic biomass sources - metabolic pathways, production enhancement, and challenges

Hydrogen production from biological processes has been hailed as a promising strategy for generating sustainable energy. Fermentative hydrogen production processes such as dark and photofermentation are considered more sustainable and economical than other biological methods such as biophotolysis. However, these methods have constraints such as low hydrogen yield and conversion efficiency, so practical implementations still need to be made. The present review provides an assessment and feasibility of producing biohydrogen through dark and photofermentation techniques utilizing various lignocellulosic biomass wastes as substrates. Furthermore, this review includes information about the strategies to increase the productivity rate of biohydrogen in an eco-friendly and sustainable manner, like integration of dark and photofermentation techniques, pretreatment of biomass, genetic modification of microorganisms, and application of nanoadditives.

Recent progress of low-temperature plasma technology in biorefining process

In recent years, low-temperature plasma-assisted processes, featuring high reaction efficiency and wide application scope, have emerged as a promising alternative to conventional methods for biomass valorization. It is well established that charged species, chemically energetic molecules and radicals, and highly active photons playing key roles during processing. This review presents the major applications of low-temperature plasma for biomass conversion in terms of (i) pretreatment of biomass, (ii) chemo fractionation of biomass into value-added chemicals, and (iii) synthesis of heterogeneous catalyst for further chemo-catalytic conversion. The pretreatment of biomass is the first and foremost step for biomass upgrading to facilitate raw biomass transformation, which reduces the crystallinity, purification, and delignification. The chemo-catalytic conversion of biomass involves primary reactions to various kinds of target products, such as hydrolysis, hydrogenation, retro-aldol condensation and so on. Finally, recent researches on plasma-assisted chemo-catalysis as well as heterogeneous catalysts fabricated via low-temperature plasma at relatively mild condition were introduced. These catalysts were reported with comparable performance for biomass conversion to other state-of-the-art catalysts prepared using conventional methods.

Improving Enzymatic Saccharification of Peach Palm (Bactris gasipaes) Wastes via Biological Pretreatment with Pleurotus ostreatus

The white-rot fungus Pleurotus ostreatus was used for biological pretreatment of peach palm (Bactris gasipaes) lignocellulosic wastes. Non-treated and treated B. gasipaes inner sheaths and peel were submitted to hydrolysis using a commercial cellulase preparation from T. reesei. The amounts of total reducing sugars and glucose obtained from the 30 d-pretreated inner sheaths were seven and five times higher, respectively, than those obtained from the inner sheaths without pretreatment. No such improvement was found, however, in the pretreated B. gasipaes peels. Scanning electronic microscopy of the lignocellulosic fibers was performed to verify the structural changes caused by the biological pretreatments. Upon the biological pretreatment, the lignocellulosic structures of the inner sheaths were substantially modified, making them less ordered. The main features of the modifications were the detachment of the fibers, cell wall collapse and, in several cases, the formation of pores in the cell wall surfaces. The peel lignocellulosic fibers showed more ordered fibrils and no modification was observed after pre-treatment. In conclusion, a seven-fold increase in the enzymatic saccharification of the Bactris gasipaes inner sheath was observed after pre-treatment, while no improvement in enzymatic saccharification was observed in the B. gasipaes peel.

Advances in microbial pretreatment for biorefining of perennial grasses

Perennial grasses are potentially abundant sources of biomass for biorefineries, which can produce high yields with low input requirements, and many added environmental benefits. However, perennial grasses are highly recalcitrant to biodegradation and may require pretreatment before undergoing many biorefining pathways. Microbial pretreatment uses the ability of microorganisms or their enzymes to deconstruct plant biomass and enhance its biodegradability. This process can enhance the enzymatic digestibility of perennial grasses, enabling saccharification with cellulolytic enzymes to produce fermentable sugars and derived fermentation products. Similarly, microbial pretreatment can increase the methanation rate when the grasses are used to produce biogas through anaerobic digestion. Microorganisms can also increase the digestibility of the grasses to improve their quality as animal feed, enhance the properties of grass pellets, and improve biomass thermochemical conversion. Metabolites produced by fungi or bacteria during microbial pretreatment, such as ligninolytic and cellulolytic enzymes, can be further recovered as added-value products. Additionally, the action of the microorganisms can release chemicals with commercialization potential, such as hydroxycinnamic acids and oligosaccharides, from the grasses. This review explores the recent advances and remaining challenges in using microbial pretreatment for perennial grasses with the goal of obtaining added-value products through biorefining. It emphasizes recent trends in microbial pretreatment such as the use of microorganisms as part of microbial consortia or in unsterilized systems, the use and development of microorganisms and consortia capable of performing more than one biorefining step, and the use of cell-free systems based on microbial enzymes. KEY POINTS: • Microorganisms or enzymes can reduce the recalcitrance of grasses for biorefining • Microbial pretreatment effectiveness depends on the grass-microbe interaction • Microbial pretreatment can generate value added co-products to enhance feasibility.

Bioprocess development for the production of xylooligosaccharide prebiotics from agro-industrial lignocellulosic waste

The development of sustainable biorefineries and bioeconomy has been the mandate of most of the governments with major focus on restricting the climate change concerns and finding new strategies to maintain the global food supply chain. Xylooligosaccharides (XOS) are short-chain oligomers which due to their excellent prebiotic potential in the nutraceutical sector has attracted intense research focus in the recent years. The agro-industrial crop and food waste can be utilized for the production of XOS which are derived from hemicellulose fraction (xylan) of the lignocellulosic materials. The extraction of xylan, is traditionally achieved by acidic and alkaline pretreatments which, however, have limited industrial applications. The inclusion of cutting-edge and environmentally beneficial pretreatment methods and technologies such as deep eutectic solvents and green catalysts are preferred. Moreover, the extraction of xylans from biomass using combinatorial pretreatment approaches may help in economizing the whole bioprocess. The current review outlines the factors involved in the xylan extraction and depolymerization processes from different lignocellulosic biomass and the subsequent enzymatic hydrolysis for XOS production. The different types of oligosaccharides and their prebiotic potential for the growth of healthy gut bacteria have also been explained. The introduction of modern molecular technologies has also made it possible to identify enzymes and microorganisms with the desired characteristics for usage in XOS industrial production processes.

Different pre-treatments and kinetic models for bioethanol production from lignocellulosic biomass: A review

Lignocellulosic biomass is the generally explored substrate to produce bioethanol for environmental sustainability due to its availability in abundance. However, the complex network of cellulose-hemicellulose-lignin present in it makes its hydrolysis as a challenging task. To boost the effectiveness of conversion, biomass is pre-treated before enzymatic hydrolysis to alter or destroy its original composition. Enzymes like Cellulases are widely used for breaking down cellulose into fermentable sugars. Enzymatic hydrolysis is a complex process involving many influencing factors such as pH, temperature, substrate concentration. This review presents major four pre-treatment methods used for hydrolysing different substrates under varied reaction conditions along with their mechanism and limitations. A relative comparison of data analysis for most widely studied 10 kinetic models is briefly explained in terms of substrates used to get the brief insight about hydrolysis rates. The summary of pre-treatment methods and hydrolysis rates including cellulase enzyme kinetics will be the value addition for upcoming researchers for optimising the hydrolysis process.

Advances in enzymatic conversion of biomass derived furfural and 5-hydroxymethylfurfural to value-added chemicals and solvents

The progress of versatile chemicals and bio-based fuels using renewable biomass has gained ample importance. Furfural and 5-hydroxymethylfurfural are biomass-derived compounds that serve as the cornerstone for high-value chemicals and have a myriad of industrial applications. Despite the significant research into several chemical processes for furanic platform chemicals conversion, the harsh reaction conditions and toxic by-products render their biological conversion an ideal alternative strategy. Although biological conversion confers an array of advantages, these processes have been reviewed less. This review explicates and evaluates notable improvements in the bioconversion of 5-hydroxymethylfurfural and furfural to comprehend the current developments in the biocatalytic transformation of furan. Enzymatic conversion of HMF and furfural to furanic derivative have been explored, while the latter has substantially overlooked a foretime. This discrepancy was reviewed along with the outlook on the potential usage of 5-hydroxymethylfurfural and furfural for the furan-based value-added products' synthesis.

Pretreatment of Arundo donax L. for photo-fermentative biohydrogen production by ultrasonication and ionic liquid

Combined pretreatment methods were assumed to further enhance photo-fermentative biohydrogen production (PFHP) from lignocellulosic biomass. For this purpose, an ultrasonication assisted ionic liquid pretreatment was applied to Arundo donax L. biomass for PFHP. The optimal condition for the combined pretreatment was 16 g/L of 1-Butyl-3-methylimidazolium Hydrogen Sulfate ([Bmim]HSO₄) combined with ultrasonication at a solid to liquid ratio (SLR) of 1:10 for 1.5 h under 60 °C. Under this condition, the maximum delignification of 22.9 % was obtained, in addition, the hydrogen yield (HY) and energy conversion efficiency (ECE) were enhanced by 1.5-fold and 46.4 % (p < 0.05) compared to untreated biomass, respectively. Moreover, heat map analysis was performed to evaluate the correlation between pretreatment conditions and corresponding results, suggesting pretreatment temperature had the strongest (absolute value of Pearson's r was 0.97) linear correlation with HY. Combined multiple energy production approaches might be useful for further improved ECE.

Effect of Microbial Consortium Constructed with Lignolytic Ascomycetes Fungi on Degradation of Rice Stubble

Microbial degradation is an effective, eco-friendly and sustainable approach for management of the rice residue. After harvesting a rice crop, removal of stubble from the ground is a challenging task, that forces the farmers to burn the residue in-situ. Therefore, accelerated degradation using an eco-friendly alternative is a necessity. White rot fungi are the most explored group of microbes for accelerated degradation of lignin but they are very slow in growth. The present investigation focuses on degradation of rice stubble using a fungal consortium constructed with highly sporulating ascomycetes fungi, namely, Aspergillus terreus, Aspergillus fumigatus and Alternaria spp. All three species were successful at colonizing the rice stubble. Periodical HPLC analysis of rice stubble alkali extracts revealed that incubation with ligninolytic consortium released various lignin degradation products such as vanillin, vanillic acid, coniferyl alcohol, syringic acid and ferulic acid. The efficiency of the consortium was further studied at different dosages on paddy straw. Maximum lignin degradation was observed when the consortium was applied at 15% volume by weight of rice stubble. Maximum activity of different lignolytic enzymes such as lignin peroxidase, laccase and total phenols was also found with the same treatment. FTIR analysis also supported the observed results. Hence, the presently developed consortium for degrading rice stubble was found to be effective in both laboratory and field conditions. The developed consortium or its oxidative enzymes can be used alone or combined with other commercial cellulolytic consortia to manage the accumulating rice stubble effectively.

Biological valorization of lignin to flavonoids

Lignin is the most affluent natural aromatic biopolymer on the earth, which is the promising renewable source for valuable products to promote the sustainability of biorefinery. Flavonoids are a class of plant polyphenolic secondary metabolites containing the benzene ring structure with various biological activities, which are largely applied in health food, pharmaceutical, and medical fields. Due to the aromatic similarity, microbial conversion of lignin derived aromatics to flavonoids could facilitate flavonoid biosynthesis and promote the lignin valorization. This review thereby prospects a novel valorization route of lignin to high-value natural products and demonstrates the potential advantages of microbial bioconversion of lignin to flavonoids. The biodegradation of lignin polymers is summarized to identify aromatic monomers as momentous precursors for flavonoid synthesis. The biosynthesis pathways of flavonoids in both plants and strains are introduced and compared. After that, the key branch points and important intermediates are clearly discussed in the biosynthesis pathways of flavonoids. Moreover, the most significant enzyme reactions including Claisen condensation, cyclization and hydroxylation are demonstrated in the biosynthesis pathways of flavonoids. Finally, current challenges and potential future strategies are also discussed for transforming lignin into various flavonoids. The holistic microbial conversion routes of lignin to flavonoids could make a sustainable production of flavonoids and improve the feasibility of lignin valorization.

Co-conversion of lignocellulose-derived glucose, xylose, and aromatics to polyhydroxybutyrate by metabolically engineered Cupriavidus necator

Utilization of all major components of lignocellulose is essential for biomass biorefining. Glucose, xylose, and lignin-derived aromatics can be generated from cellulose, hemicellulose, and lignin of lignocellulose degradation through pretreatment and hydrolysis. In present work, Cupriavidus necator H16 was engineered to utilize glucose, xylose, p-coumaric acid, and ferulic acid simultaneously by multi-step genetic engineering. Firstly, genetic modification and adaptive laboratory evolution were performed to promote glucose transmembrane transport and metabolism. Xylose metabolism was then engineered by integrating genes xylAB (xylose isomerase and xylulokinase) and xylE (proton-coupled symporter) in the locus of ldh (lactate dehydrogenase) and ackA (acetate kinase) on the genome, respectively. Thirdly, p-coumaric acid and ferulic acid metabolism was achieved by constructing an exogenous CoA-dependent non-β-oxidation pathway. Using corn stover hydrolysates as carbon sources, the resulting engineered strain Reh06 simultaneously converted all components of glucose, xylose, p-coumaric acid, and ferulic acid to produce 11.51 g/L polyhydroxybutyrate.

Degradation of lignin in different lignocellulosic biomass by steam explosion combined with microbial consortium treatment

The difficulty of degrading lignin is the main factor limiting the high-value conversion process of lignocellulosic biomass. The biodegradation of lignin has attracted much attention because of its strong environmental friendliness, but it still faces some dilemmas such as slow degradation rate and poor adaptability. The microbial consortia with high lignin degradation efficiency and strong environmental adaptability were obtained in our previous research. To further increase the lignin degradation efficiency, this paper proposes a composite treatment technology of steam explosion combined with microbial consortium degradation to treat three kinds of biomass. We measured the lignin degradation efficiency, selectivity value (SV) and enzymatic saccharification efficiency. The structural changes of the biomass materials and microbial consortium structure were also investigated. The experimental results showed that after 1.6 MPa steam explosion treatment, the lignin degradation efficiency of the eucalyptus root reached 35.35% on the 7th days by microbial consortium. At the same time, the lignin degradation efficiency of the bagasse and corn straw treated by steam explosion followed by microbial biotreatment was 37.61-44.24%, respectively, after only 7 days of biotreatment. The microbial consortium also showed strong selectivity degradation to lignin. The composite treatment technology can significantly improve the enzymatic saccharification efficiency. Saccharomycetales, Ralstonia and Pseudomonadaceae were the dominant microorganisms in the biomass degradation systems. It was proved that the combined treatment technology of steam explosion and microbial consortium degradation could overcome the drawbacks of traditional microbial pretreatment technology, and can facilitate the subsequent high-value conversion of lignocellulose.

Evaluating the Impact of Cellulose Extraction via Traditional and Ionosolv Pretreatments from Domestic Matchstick Waste on the Properties of Carboxymethyl Cellulose

Carboxymethyl cellulose (CMC) is a hydrophilic derivative of cellulose whose large volumes have been used in textile processing, protective coatings, detergents, papers, and drilling fluids, while cellulose gum, which is the purified form of CMC, has extensive applications in food, cosmetic, and pharmaceutical industries. Therefore, this work reflects the production of CMC by extracting cellulose with traditional and ionosolv methods from domestic matchstick waste, providing an in-depth view of the overall process where two different kinds of cellulose were obtained from two different pretreatments, and the influence of cellulose on the profile of CMC was checked. All of the procedures have been performed under optimized conditions to reduce the cost and maximize the productiveness. The results depict that cellulose extracted by the ionosolv method using a protic ionic liquid, tetramethylguanidinium hydrogen sulfate (TMG-HSO₄), is more degraded than that extracted by the traditional sulfide method using sodium sulfide (Na₂S) and sodium hydroxide (NaOH). Thus, the produced CMC-2 via ionic liquid-extracted cellulose has more yield, DS (2.3), purity (98.5%), and solubility with less salt and moisture contents than CMC-1 produced by the conventional method due to an effective substitution of the hydroxyl group by the carboxymethyl group. Further, instrumental analyses like FTIR, XRD, ¹H NMR, ¹³C NMR, and SEM emphasize the results that CMC-2 has more reduction of the hydroxyl peak in FTIR, a more amorphous structure in XRD, intense peaks in NMR, and the roughness of the surface in SEM.

Biological pretreatment of sugarcane bagasse for the production of fungal laccase and bacterial cellulase

Sugarcane bagasse (SB) is a promising source of appreciable quantities of fermentable sugars. However, the presence of lignin hinders utilization of these carbohydrates and hence pretreatment to remove lignin is necessarily carried out. Here, a biological pretreatment method was synchronized with the production of a thermostable cellulase using SB as a raw material. Initially, bagasse was fermented by a laccase producing fungus, Trametes pubescens MB 89 under solid state fermentation (SSF) and a titer of 1758 IU mL^-1 of laccase was obtained. Investigations of nine factors affecting laccase production through Plackett Burman design improved the titers to 6539 IU mL^-1 . Five factors (incubation period, concentration of CuSO₄ , temperature, moisture content, and particle size) were found significant which were optimized through Central Composite design leading to an improvement in the titers by ~5 folds (8841 IU mL^-1 ). Biologically pretreated SB was fermented by a thermophilic bacterium, Neobacillus sedimentimangrovi UE25, that yielded 8.64 IU mL^-1 of cellulase. Delignification and cellulose utilization were affirmed by structural analysis through FTIR and SEM. The synchronized process yielded higher titers of laccase and cellulase under SSF of SB with the minimum use of corrosive chemicals.

The potential of imidazole as a new solvent in the pretreatment of agro-industrial lignocellulosic biomass

Lignocellulosic biomass is a renewable material of great abundance. However, its recalcitrant characteristic requires the application of pretreatments. Sugarcane bagasse (SB), soybean hulls (SH), cocoa pod husks (CPH) and oil palm empty fruit bunches (OPEFB) were subjected to imidazole pretreatment in order to evaluate chemical composition variations and influence over enzymatic hydrolysis efficiency. Non-treated SH, SB and OPEFB have higher content of holocellulose, while CPH is rich in lignin polymers (31.2%). After imidazole-pretreatment, all biomasses presented structural disorganization of lignocellulosic fibres and enrichment in the percentage of cellulose. Levels of up to 72% delignification were obtained, which allowed an enzymatic conversion greater than 95% for SB, SH and OPEFB, while only 83% was reached for CPH. Imidazole is then emerging as a potential catalyst for the pretreatment of agro-industrial by-products, allowing the valorisation of these residues and their reinsertion into the production chain under a biorefinery concept.

Lignocellulosic Biorefinery Technologies: A Perception into Recent Advances in Biomass Fractionation, Biorefineries, Economic Hurdles and Market Outlook

Lignocellulosic biomasses (LCB) are sustainable and abundantly available feedstocks for the production of biofuel and biochemicals via suitable bioconversion processing. The main aim of this review is to focus on strategies needed for the progression of viable lignocellulosic biomass-based biorefineries (integrated approaches) to generate biofuels and biochemicals. Processing biomass in a sustainable manner is a major challenge that demands the accomplishment of basic requirements relating to cost effectiveness and environmental sustainability. The challenges associated with biomass availability and the bioconversion process have been explained in detail in this review. Limitations associated with biomass structural composition can obstruct the feasibility of biofuel production, especially in mono-process approaches. In such cases, biorefinery approaches and integrated systems certainly lead to improved biofuel conversion. This review paper provides a summary of mono and integrated approaches, their limitations and advantages in LCB bioconversion to biofuel and biochemicals.

Effective hydrolysis for waste plant biomass impacts sustainable fuel and reduced air pollution generation: A comprehensive review

Among various natural biowastes availability in the environment, agricultural residues showed great impacts. It is due to huge availability and cheap carbon source, creating big challenges for their utility and systematic reduction. Objective of this review is to address the waste biomass availability and huge quantities issues and also put effort to minimize this nutrient load via biotransforming into value-added products. Different wastes (organic/inorganic) generation with their negative issues are due to numbers of developmental and social activities, reported. Currently, various efforts are found for these wastes minimization via generation of different types of value-added products (biogas, bioH₂, alcoholic fuel, organic acids and others products) and these wastes in municipal cities are also reported with production of advanced biofuels as promising outcomes. For hydrolysis of complex organic resources including lignocellulosic biomasses, physicochemical, structural or compositional changes are needed that aid in conversion into sugar and organic compounds such as biofuels. So, efficient and effective pretreatment processes selection (physical, biological, chemical or combined one) is critical to achieve these hydrolysis goals and resultant cellulose or hemicellulose components can be accessible by biological catalysis. These can achieve final hydrolysis and fermentative or monomer sugars. And later, synthesis of fuels or value-added products during microbial fermentation or biotransformation processes can be achieved. This review discusses pretreatment techniques for improved hydrolysis for fermentative sugar with emphasis on reduced quantities of toxic compounds (furfural compound) in hydrolyzed biomasses. Minimum deterioration fuel economy also reported with production of different bioproducts including biofuels. Additionally, impacts of toxic products and gasses emission are also discussed with their minimization.

High solids loading pretreatment: The core of lignocellulose biorefinery as an industrial technology - An overview

Pretreatment is the first and most determinative, yet the least mature step of lignocellulose biorefinery chain. The current stagnation of biorefinery commercialization indicates the barriers of the existing pretreatment technologies are needed to be unlocked. This review focused on one of the core factors, the high lignocellulose solids loading in pretreatment. The high solids loading of pretreatment significantly reduces water input, energy requirement, toxic compound discharge, solid/liquid separation costs, and carbon dioxide emissions, improves the titers of sugars and biproducts to meet the industrial requirements. Meanwhile, lignocellulose feedstock after high solids loading pretreatment is compatible with the existing logistics system for densification, packaging, storage, and transportation. Both the technical-economic analysis and the cellulosic ethanol conversion performance suggest that the solids loading in the pretreatment step need to be further elevated towards an industrial technology and the effective solutions should be proposed to the technical barriers in high solids loading pretreatment operations.

Impact of nanomaterials on sustainable pretreatment of lignocellulosic biomass for biofuels production: An advanced approach

Biomass to biofuels production technology appears to be one of the most sustainable strategies among various renewable energy resources. Herein, pretreatment is an unavoidable and key step to increase free cellulose availability and digestibility to produce green fuels. Various existing pretreatment technologies of lignocellulosics biomasses (LCBs) face distinct challenges e.g., energy consuming, cost intensive, may lead partial removal of lignin, complex inhibitors production as well as may cause environmental pollutions. These, limitations may be overcome with the application of nanomaterials, employed as nanocatalysts during the pretreatment process of LCBs. In this prospect, the present review focuses and summarizes results of numerous studies and exploring the utilizations of magnetic, carbon based nanostructure, and nanophotocatalysts mediated pretreatment processes along with their possible mechanisms to improve the biofuels production compared to conventional chemical based pretreatment approaches. Furthermore, different aspects of nanomaterials based pretreatment methods with their shortcomings and future prospects have been discussed.

Nature-inspired pretreatment of lignocellulose - Perspective and development

As sustainability gains increasing importance in addition to cost-effectiveness as a criterion for evaluating engineering systems and practices, biological processes for lignocellulose pretreatment have attracted growing attention. Biological systems such as white and brown rot fungi and wood-consuming insects offer fascinating examples of processes and systems built by nature to effectively deconstruct plant cell walls under environmentally benign and energy-conservative environments. Research in the last decade has resulted in new knowledge that advanced the understanding of these systems, provided additional insights into these systems' functional mechanisms, and demonstrated various applications of these processes. The new knowledge and insights enable the adoption of a nature-inspired strategy aiming at developing technologies that are informed by the biological systems but superior to them by overcoming the inherent weakness of the natural systems. This review discusses the nature-inspired perspective and summarizes related advancements, including the evolution from biological systems to nature-inspired processes, the features of biological pretreatment mechanisms, the development of nature-inspired pretreatment processes, and future perspective. This work aims to highlight a different strategy in the research and development of novel lignocellulose pretreatment processes and offer some food for thought.

Pretreatments of lignocellulosic and algal biomasses for sustainable biohydrogen production: Recent progress, carbon neutrality, and circular economy

Lignocellulosic and algal biomasses are known to be vital feedstocks to establish a green hydrogen supply chain toward achieving a carbon-neutral society. However, one of the most pressing issues to be addressed is the low digestibility of these biomasses in biorefinery processes, such as dark fermentation, to produce green hydrogen. To date, various pretreatment approaches, such as physical, chemical, and biological methods, have been examined to enhance feedstock digestibility. However, neither systematic reviews of pretreatment to promote biohydrogen production in dark fermentation nor economic feasibility analyses have been conducted. Thus, this study offers a comprehensive review of current biomass pretreatment methods to promote biohydrogen production in dark fermentation. In addition, this review has provided comparative analyses of the technological and economic feasibility of existing pretreatment techniques and discussed the prospects of the pretreatments from the standpoint of carbon neutrality and circular economy.

Xylopentose production from crop residue employing xylanase enzyme

To produce xylo-oligosaccharides (XOS) from the agriculture waste, which included, green coconut and vegetable cocktail. The two pretreatment - hydrogen peroxide-acetic acid (HP-AC) and sodium hypochlorite-sodium hydroxide (SH-SH) - were used for this study. The optimal conditions for the pretreatment were 80 °C, 4.0 % NaClO, and 2 h, followed by 0.08 % NaOH, 55 °C, and 1 h. Further enzymatic hydrolysis of green coconut (GC) and vegetable cocktail (VC) were performed and found in case of GC, the best outcomes were observed. Different types of XOS were obtained from the treated biomass whereas a single type of XOS xylo-pentose was obtained in high quantity (96.44 % and 93.09 % from CG and VC respectively) with the production of other XOS < 2 %. This study presents a reasonably secure and economical method for turning secondary crop residue into XOS and fermentable sugars.

Anaerobic digestion of fruit and vegetable waste: a critical review of associated challenges

The depletion of fossil fuels coupled with stringent environmental laws has encouraged us to develop sustainable renewable energy. Due to its numerous benefits, anaerobic digestion (AD) has emerged as an environment-friendly technology. Biogas generated during AD is primarily a mixture of CH₄ (65-70%) and CO₂ (20-25%) and a potent energy source that can combat the energy crisis in today's world. Here, an attempt has been made to provide a broad understanding of AD and delineate the effect of various operational parameters influencing AD. The characteristics of fruit and vegetable waste (FVW) and its feasibility as a potent substrate for AD have been studied. This review also covers traditional challenges in managing FVW via AD, the implementation of various bioreactor systems to manage large amounts of organic waste and their operational boundaries, microbial consortia involved in each phase of digestion, and various strategies to increase biogas production.

Rapid lignin quantification for fungal wood pretreatment by ATR-FTIR spectroscopy

Lignin determination in lignocellulose with the conventional two-step acid hydrolysis method is highly laborious and time-consuming. However, its quantification is crucial to monitor fungal pretreatment of wood, as the increase of acid-insoluble lignin (AIL) degradation linearly correlates with the achievable enzymatic saccharification yield. Therefore, in this study, a new attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy method was developed to track fungal delignification in an easy and rapid manner. Partial least square regression (PLSR) with cross-validation (CV) was applied to correlate the ATR-FTIR spectra with the AIL content (19.9 %-27.1 %). After variable selection and normalization, a PLSR model with a high coefficient of determination (R_CV² = 0.87) and a low root mean square (RMSECV = 0.60 %) were obtained despite the heterogeneous nature of the fungal solid-state fermentation. These results show that ATR-FTIR can reliably predict the AIL content in fungus-treated wood while being a high-throughput method. This novel method can facilitate the transition to the wood-based economy.

Conversion of lignocellulosic biomass: Production of bioethanol and bioelectricity using wheat straw hydrolysate in electrochemical bioreactor

The present study evaluated efficiency of wheat straw (WS) hydrolysate obtained through fungal pre-treatment to produce ethanol and electricity in an electrochemical bioreactor. Three white rot fungi Phanerochaete chrysosporium, Phlebia floridensis and Phlebia brevispora were used to degrade WS for hydrolysate preparation, Lignocellulolytic enzyme production was also monitored during the pretreatment. Yeast Pichia fermentans was allowed to ferment all three hydrolysates up to 12 days. The yeast showed maximum electrochemical response as open circuit voltage (0.672 V), current density 542.42 mA m^-2, and power density of 65.09 mW m^-2 on 12th day in the hydrolysate prepared using Phlebia floridensis. Maximum ethanol production of 9.2% (w/v) was achieved on 7th day with a fermentation efficiency of about 62.1%. Further, the coulombic efficiency improved from 0.06 to 1.46% during 12 days of the experiment. Thus, the results indicated towards the possible conversion of lignocellulosic biomass into bioethanol along with bioelectricity generation.

Insight into pathway of monosaccharide production from integrated enzymatic hydrolysis of rice straw waste as feed stock for anaerobic digestion

This research examined the possible pathway of monosaccharide production from the rice straw waste using three integrated enzymatic hydrolysis approaches: boiled hot water pre-treatment with enzyme, alkaline pre-treatment with enzyme, and acid pre-treatment with enzyme, that can be further used as the feedstock for anaerobic digestion. Two cellulase enzymes: SIGMA-ALDRICH laboratory grade cellulase from Aspergillus niger and atres Zymix plus as a commercial cellulase enzyme were applied. It was found that the boiled hot water pre-treatment with the commercial cellulase gave the highest total monosaccharides yields. Glucose was the most significant part (78-86%) of the monosaccharides. For the pre-treatment with dilute acid, glucose was also the main component of monosaccharides; however, for the alkali pre-treatment, xylose was the main monosaccharide. It made up 48-85% of the total monosaccharide compared to glucose that made up 5-49% of total monosaccharide. Boiled rice straw with commercial cellulase enzyme provided the highest glucose yield compared to other experiments. Moreover, the obtained results from GC-MS/MS analysis show that up to 62 species of phenolic compound could be found in enzymatic hydrolysis of the rice straw waste. Aromatic and aliphatic hydrocarbon substances were also detected in the FEEM analysis. From the overall results, the integrated enzymatic hydrolysis with boil hot water pre-treatment was the most efficient method for monosaccharide production from the rice straw waste.

Review of chemical pretreatment of lignocellulosic biomass using low-liquid and low-chemical catalysts for effective bioconversion

Chemical pretreatment of lignocellulosic biomass (LCB) is essential for effective biological conversion in subsequent steps to produce biofuels or biochemicals. For effective pretreatment, high lignin content and its recalcitrant nature of LCB are major factors influencing bioconversion, especially lignin is known to be effectively solubilized by alkaline, organic, and deep eutectic solvents, ionic liquids, while hemicellulose is effectively dissolved by various acid catalysts and organic solvents. Depending on the pretreatment method/catalyst used, different pretreatment process scheme should be applied with different amounts of catalyst and water inputs to achieve a satisfactory effect. In addition, the amount of processing water required in the following processes such as washing, catalyst recovery, and conditioning after pretreatment is critical factor for scale-up (commercialization). In this review, the amount of catalyst and/or water used, and the effect of pretreatment, properties of the products, and recovery of liquid are also discussed.

Multi-omics network model reveals key genes associated with p-coumaric acid stress response in an industrial yeast strain

The production of ethanol from lignocellulosic sources presents increasingly difficult issues for the global biofuel scenario, leading to increased production costs of current second-generation (2G) ethanol when compared to first-generation (1G) plants. Among the setbacks encountered in industrial processes, the presence of chemical inhibitors from pre-treatment processes severely hinders the potential of yeasts in producing ethanol at peak efficiency. However, some industrial yeast strains have, either naturally or artificially, higher tolerance levels to these compounds. Such is the case of S. cerevisiae SA-1, a Brazilian fuel ethanol industrial strain that has shown high resistance to inhibitors produced by the pre-treatment of cellulosic complexes. Our study focuses on the characterization of the transcriptomic and physiological impact of an inhibitor of this type, p-coumaric acid (pCA), on this strain under chemostat cultivation via RNAseq and quantitative physiological data. It was found that strain SA-1 tend to increase ethanol yield and production rate while decreasing biomass yield when exposed to pCA, in contrast to pCA-susceptible strains, which tend to decrease their ethanol yield and fermentation efficiency when exposed to this substance. This suggests increased metabolic activity linked to mitochondrial and peroxisomal processes. The transcriptomic analysis also revealed a plethora of differentially expressed genes located in co-expressed clusters that are associated with changes in biological pathways linked to biosynthetic and energetical processes. Furthermore, it was also identified 20 genes that act as interaction hubs for these clusters, while also having association with altered pathways and changes in metabolic outputs, potentially leading to the discovery of novel targets for metabolic engineering toward a more robust industrial yeast strain.

Bioactive compounds of Curvularia species as a source of various biological activities and biotechnological applications

Many filamentous fungi are known to produce several secondary metabolites or bioactive compounds during their growth and reproduction with sort of various biological activities. Genus Curvularia (Pleosporaceae) is a dematiaceous filamentous fungus that exhibits a facultative pathogenic and endophytic lifestyle. It contains ~213 species among which Curvularia lunata, C. geniculata, C. clavata, C. pallescens, and C. andropogonis are well-known. Among them, C. lunata is a major pathogenic species of various economical important crops especially cereals of tropical regions while other species like C. geniculata is of endophytic nature with numerous bioactive compounds. Curvularia species contain several diverse groups of secondary metabolites including alkaloids, terpenes, polyketides, and quinones. Which possess various biological activities including anti-cancer, anti-inflammatory, anti-microbial, anti-oxidant, and phytotoxicity. Several genes and gene factors are involved to carry and regulate the expression of these activities which are influenced by environmental signals. Some species of Curvularia also show negative impacts on humans and animals. Apart from their negative effects, there are some beneficial implications like production of enzymes of industrial value, bioherbicides, and source of nanoparticles is reported. Many researchers are working on these aspects all over the world but there is no review in literature which provides significant understanding about these all aspects. Thus, this review will provide significant information about secondary metabolic diversity, their biological activities and biotechnological implications of Curvularia species.

Integrating 1G with 2G Bioethanol Production by Using Distillers’ Dried Grains with Solubles (DDGS) as the Feedstock for Lignocellulolytic Enzyme Production

First-generation (1G) bioethanol is one of the most used liquid biofuels in the transport industry. It is generated by using sugar- or starch-based feedstocks, while second-generation (2G) bioethanol is generated by using lignocellulosic feedstocks. Distillers’ dried grains with solubles (DDGS) is a byproduct of first-generation bioethanol production with a current annual production of 22.6 million tons in the USA. DDGS is rich in fiber and valuable nutrients contents, which can be used to produce lignocellulolytic enzymes such as cellulases and hemicellulases for 2G bioethanol production. However, DDGS needs a pretreatment method such as dilute acid, ammonia soaking, or steam hydrolysis to release monosaccharides and short-length oligosaccharides as fermentable sugars for use in microbial media. These fermentable sugars can then induce microbial growth and enzyme production compared to only glucose or xylose in the media. In addition, selection of one or more suitable microbial strains, which work best with the DDGS for enzyme production, is also needed. Media optimization and fermentation process optimization strategies can then be applied to find the optimum conditions for the production of cellulases and hemicellulases needed for 2G bioethanol production. Therefore, in this review, a summary of all such techniques is compiled with a special focus on recent findings obtained in previous pieces of research conducted by the authors and by others in the literature. Furthermore, a comparison of such techniques applied to other feedstocks and process improvement strategies is also provided. Overall, dilute acid pretreatment is proven to be better than other pretreatment methods, and fermentation optimization strategies can enhance enzyme production by considerable folds with a suitable feedstock such as DDGS. Future studies can be further enhanced by the technoeconomic viability of DDGS as the on-site enzyme feedstock for the manufacture of second-generation bioethanol (2G) in first-generation (1G) ethanol plants, thus bridging the two processes for the efficient production of bioethanol using corn or other starch-based lignocellulosic plants.

Evaluating the potential of engineered Trichoderma atroviride and its laccase-mediated system for the efficient bioconversion of 5-hydroxymethylfufural

5-Hydroxymethylfurfural (HMF) is a fermentation inhibitor which is formed during acid-based thermochemical pre-treatment of biomass. The present study involves two approaches for HMF conversion; the first includes screening and identification of fungal strains which produce oxidoreductases for HMF bioconversion, and thereafter evaluating their roles in HMF conversion. Out of the ten fungal strains screened, genetically engineered Trichoderma atroviride (Lac⁺) showed maximum HMF bioconversion and the activities of ligninolytic enzymes produced were noted. Maximum HMF conversion of 99% was achieved at pH 5.0 and 30 °C when 72 h old 10% inoculum of T. atroviride (Lac⁺) was utilized for 6 days. Based on the fungal bioconversion of HMF to 2, 5 diformylfuran with 58% yield, laccase was observed to influence the conversion process. Thus, a comparative study was established on HMF conversion by 100 U/mL of commercial laccases and partially purified laccase from T. atroviride (Lac+). In the presence of TEMPO, T. atroviride laccase showed comparable HMF conversion to commercial laccases, which establishes the efficiency of fungi and ligninolytic enzymes in bioconversion of HMF to value-added products.

Integrative biohydrogen- and biomethane-producing bioprocesses for comprehensive production of biohythane

The production of biohythane, a combination of energy-dense hydrogen and methane, from the anaerobic digestion of low-cost organic wastes has attracted attention as a potential candidate for the transition to a sustainable circular economy. Substantial research has been initiated to upscale the process engineering to establish a hythane-based economy by addressing major challenges associated with the process and product upgrading. This review provides an overview of the feasibility of biohythane production in various anaerobic digestion systems (single-stage, dual-stage) and possible technologies to upgrade biohythane to hydrogen-enriched renewable natural gas. The main goal of this review is to promote research in biohythane production technology by outlining critical needs, including meta-omics and metabolic engineering approaches for the advancements in biohythane production technology.

Valorization of jackfruit waste into value added products and their potential applications

Jackfruit is a potential natural resource for many valuable biomaterials. The wastes from jackfruit are rich in carbohydrate, proteins, fats and phytochemicals. These wastes can be used as feedstock for the development of various bioproducts. The pretreatment strategies like biological, physical and chemical methods are being used for effective valorization of fruit wastes into value added products, like bioethanol, biogas, bioplastics, feeds, functional food additives, and other useful compounds. Bioenergy production from such renewable resources is an eco-friendly and cost-effective alternative option of fuels, unlike fossil fuels. The efficient bioconversion of fruit waste into useful biomaterials is facilitated by microbial fermentation process. Also, jackfruit peel is applied in the pollution abatement by remediation of dyes color from contaminated aquatic environment. Such technology can be used to develop a green economic model for waste utilization. This review addressed the utilization feasibility of jackfruit waste to produce value added products in order to reduce wastes and protect environment in a sustainable way.

Capture Hi-C reveals the influence on dynamic three-dimensional chromosome organization perturbed by genetic variation or vanillin stress in Saccharomyces cerevisiae

Studying the mechanisms of resistance to vanillin in microorganisms, which is derived from lignin and blocks a major pathway of DNA double-strand break repair in yeast, will benefit the design of robust cell factories that produce biofuels and chemicals using lignocellulosic materials. A high vanillin-tolerant Saccharomyces cerevisiae strain EMV-8 carrying site mutations compared to its parent strain NAN-27 was selected for the analyses. The dynamics of the chromatin structure of eukaryotic cells play a critical role in transcription and the regulation of gene expression and thus the phenotype. Consequently, Hi-C and transcriptome analyses were conducted in EMV-8 and NAN-27 in the log phase with or without vanillin stress to determine the effects of mutations and vanillin disturbance on the dynamics of three-dimensional chromosome organization and the influence of the organization on the transcriptome. The outcomes indicated that the chromosome interaction pattern disturbed by vanillin stress or genetic mutations in the log phase was similar to that in mouse cells. The short chromosomes contact the short chromosomes, and the long chromosomes contact the long chromosomes. In response to vanillin stress, the boundaries of the topologically associating domain (TAD) in the vanillin-tolerant strain EMV-8 were more stable than those in its parent strain NAN-27. The motifs of SFL1, STB3, and NHP6A/B were enriched at TAD boundaries in both EMV-8 and NAN-27 with or without vanillin, indicating that these four genes were probably related to TAD formation. The Indel mutation of YRR1, whose absence was confirmed to benefit vanillin tolerance in EMV-8, caused two new interaction sites that contained three genes, WTM2, PUP1, and ALE1, whose overexpression did not affect vanillin resistance in yeast. Overall, our results revealed that in the log phase, genetic mutations and vanillin disturbance have a negligible effect on three-dimensional chromosome organization, and the reformation or disappearance of TAD boundaries did not show an association with gene expression, which provides an example for studying yeast chromatin structure during stress tolerance using Hi-C technology.