Biological pretreatment of lignocellulosic biomass--An overview

Improvement of empty palm fruit bunches biodegradability and biogas production by integrating the straw mushroom cultivation as a pretreatment in the solid-state anaerobic digestion

Empty fruit bunches (EFB) have low biodegradability and restrict their commercial utilization in biogas plants. Integration of straw mushroom (Volvariella volvacea) cultivation as a function of bio-pretreatment on EFB to improve biodegradability and methane production by solid-state anaerobic digestion (SS-AD) was investigated. The mushroom yield was 47.3 kg·tonne^-1 EFB with remaining weight in spent mushroom-EFB (S-mEFB) of 82%. The cellulose, hemicellulose, and lignin of EFB were degraded by 3.3%, 21.3%, and 17.6%, respectively, with an increased surface area of S-mEFB. The biodegradability of S-mEFB (62.7%) was 2 times higher than raw EFB (33.5%) with the highest methane yield and production of 281 mL CH₄·g^-1 VS and 50.6 m³·tonne^-1 S-mEFB, respectively. The co-digestion of S-mEFB with 5% v/w POME had highest methane yield of 405 mL CH₄·g^-1 VS with biodegradability of 90.8%. Integrating straw mushroom cultivation with SS-AD is a promising strategy for achieving an environmentally friendly and economically feasible process.

Catalytic conversion of corncob to furfuryl alcohol in tandem reaction with tin-loaded sulfonated zeolite and NADPH-dependent reductase biocatalyst

In this study, tin-loaded sulfonated zeolite (Sn-zeolite) catalyst was synthesized for catalysis of raw corncob (75.0 g/L) to 103.0 mM furfural at 52.3% yield in water (pH 1.0) at 170 °C. This corncob-derived furfural was subsequently biotransformed with recombinant E. coli CG-19 cells coexpressing NADPH-dependent reductase and glucose dehydrogenase at 35 °C by supplementary of glucose (1.5 mol glucose/mol furfural), sodium dodecyl sulfate (0.50 mM) and NADP⁺ (1.0 μmol NADP⁺/mmol furfural) in the aqueous catalytic media (pH 7.5). Both sodium dodecyl sulfate (0.50 mM) and Sn⁴⁺ (1.0 mM) could promote reductase activity by 1.4-folds. Within 3 h, furfural was wholly catalyzed into furfuryl alcohol. By combining chemical catalysis with Sn-zeolite and biocatalysis with CG-19 cells in one-pot, an effective and sustainable process was established for tandemly catalyzing renewable biomass into furfuryl alcohol under environmentally-friendly way.

Biological Characterization and Instrumental Analytical Comparison of Two Biorefining Pretreatments for Water Hyacinth (Eichhornia crassipes) Biomass Hydrolysis

Water hyacinth is a rapidly growing troublesome aquatic weed plant, which causes eutrophication in water bodies and irreversible damage to the ecological system. In this work, we have investigated the water hyacinth biomass (WHB) hydrolysis efficacy of dilute alkaline (DA) pretreatment followed by biological pretreatment with white-rot fungus Alternaria alternata strain AKJK-2. The effectiveness of the dilute alkaline (DA) and biological pretreatment process on WHB was confirmed by using X-ray Diffraction (XRD) and Fourier Transform Infrared Spectrophotometer (FTIR), and was further visualized by Scanning Electron Microscope (SEM) and Confocal Laser Scanning Microscopy (CLSM). XRD spectra showed the increase in the crystallinity of pretreated samples, attributed to the elimination of amorphous components as lignin and hemicellulose. FTIR peak analysis of pre-treated WHB showed substantial changes in the absorption of cellulose functional groups and the elimination of lignin signals. Scanning electron microscopy (SEM) images showed firm, compact, highly ordered, and rigid fibril structures without degradation in the untreated WHB sample, while the pretreated samples exhibited loose, dispersed, and distorted structures. XRD indices (Segal, Landis, and Faneite), and FTIR indices [Hydrogen bond intensity (HBI); Total crystallinity index (TCI); and Lateral order crystallinity (LOI)] results were similar to the aforementioned results, and also showed an increase in the crystallinity both in alkaline and biological pretreatments. Alkaline pretreated WHB, with these indices, also showed the highest crystallinity and a crystalline allomorphs mixture of cellulose I (native) and cellulose II. These results were further validated by the CLSM, wherein fluorescent signals were lost after the pretreatment of WHB over control. Overall, these findings showed the significant potential of integrated assessment tools with chemical and biological pretreatment for large-scale utilization and bioconversion of this potential aquatic weed for bioenergy production.

Effect of Severity Factor on the Subcritical Water and Enzymatic Hydrolysis of Coconut Husk for Reducing Sugar Production

Preventing the further degradation of monomeric or oligomeric sugar into by-product during biomass conversion is one of the challenges for fermentable sugar production. In this study, the performance of subcritical water (SCW) and enzymatic hydrolysis of coconut husk toward reducing sugar production was investigated using a severity factor (SF) approach. Furthermore, the optimal condition of SCW was optimized using response surface methodology (RSM), where the composition changes of lignocellulose and sugar yield as responses. From the results, at low SF of SCW, sugar yield escalated as increasing SF value. In the enzymatic hydrolysis process, the effect of SCW pressure is a significant factor enhancing sugar yield. A maximum total sugar yield was attained on the mild SF condition of 2.86. From this work, it was known that the SF approach is sufficient parameter to evaluate the SCW and enzymatic hydrolysis of coconut husk. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Ideal Feedstock and Fermentation Process Improvements for the Production of Lignocellulolytic Enzymes

The usage of lignocellulosic biomass in energy production for biofuels and other value-added products can extensively decrease the carbon footprint of current and future energy sectors. However, the infrastructure in the processing of lignocellulosic biomass is not well-established as compared to the fossil fuel industry. One of the bottlenecks is the production of the lignocellulolytic enzymes. These enzymes are produced by different fungal and bacterial species for degradation of the lignocellulosic biomass into its reactive fibers, which can then be converted to biofuel. The selection of an ideal feedstock for the lignocellulolytic enzyme production is one of the most studied aspects of lignocellulolytic enzyme production. Similarly, the fermentation enhancement strategies for different fermentation variables and modes are also the focuses of researchers. The implementation of fermentation enhancement strategies such as optimization of culture parameters (pH, temperature, agitation, incubation time, etc.) and the media nutrient amendment can increase the lignocellulolytic enzyme production significantly. Therefore, this review paper summarized these strategies and feedstock characteristics required for hydrolytic enzyme production with a special focus on the characteristics of an ideal feedstock to be utilized for the production of such enzymes on industrial scales.

Saccharogenic refining of Ginkgo biloba leaf residues using a cost-effective enzyme cocktail prepared by the fungal strain A32 isolated from ancient ginkgo biloba tree

To reduce environmental pollution and waste of biomass from Ginkgo biloba leaf residues (GBLRs), we developed a cost-effective enzyme system to hydrolyze GBLRs into available reducing sugars (RS). Biomass characteristics of GBLRs were investigated, which indicated that the acid hydrolyzed fraction was 49.43% of the dry weight of GBLRs. The fraction could be effectively converted into RS by an enzyme cocktail with high polygalacturonase activity without traditionally intricate pretreatment. The strain A32 isolated from the ancient ginkgo soil was used for the production of the enzyme cocktail, and a response surface methodology was used to optimize the enzymatic production. The enzyme cocktail released 87.2% of RS from GBLRs at 35 ℃ for 72 h with 1% (m/v) of loading, and the RS concentration arrived 8.95 ± 0.39 mg/ml with 9% of GBLRs loading. The cost-effective system of self-prepared enzyme cocktail is promising for facilitating GBLRs' bio-based industry.

Swine manure valorization in fabrication of nutrition and energy

Renewable energy can boost the growing population's need and rapid budgetary development. To reduce fossil fuel consumption is the initial purpose of renewable and sustainable energy, producing valuable bio-based products. The fermenters, using for pretreatment of swine manure, and involvement of swine carcasses are reported to enhance organic loading rate followed by improved biogas yield on household digesters. The compositions such as animal residues, pathogenic microbes, pharmaceutical residues and nutrient compositions including undigested feed are still confused. Therefore, it is mandatory to optimize and stabilize anaerobic practice and digestate filtration purification for consequential fertilizer consumption. The effective bio-methane recovery from energy-rich compounds is challenging due to slow degradation procedures. The pretreatment procedure could enhance lipid depolymerization and improve anaerobic fermentation. This article deeply focuses on biodegradation of swine manure. The components of this manure were evaluated and established several approaches to improve biogas production. Furthermore, recycling of co-digestates was discussed in detail as fertilizer consumption including hygienic aspects of manure and pretreatment strategies of biomass residues. KEY POINTS: • Co-digestion of manure and carcasses enhance bio-methane production. • Removel of ammonia from biogas digester may improve bio-methane gas. • A strong antimicrobial influence has been reported on biogas production.

Biotransformation of lignocellulosic biomass into industrially relevant products with the aid of fungi-derived lignocellulolytic enzymes

Lignocellulosic material has drawn significant attention among the scientific community due to its year-round availability as a renewable resource for industrial consumption. Being an economic substrate alternative, various industries are reevaluating processes to incorporate derived compounds from these materials. Varieties of fungi and bacteria have the ability to depolymerize lignocellulosic biomass by synthesizing degrading enzymes. Owing to catalytic activity stability and high yields of conversion, lignocellulolytic enzymes derived from fungi currently have a high spectrum of industrial applications. Moreover, these materials are cost effective, eco-friendly and nontoxic while having a low energy input. Techno-economic analysis for current enzyme production technologies indicates that synthetic production is not commercially viable. Instead, the economic projection of the use of naturally-produced ligninolytic enzymes is promising. This approach may improve the economic feasibility of the process by lowering substrate expenses and increasing lignocellulosic by-product's added value. The present review will discuss the classification and enzymatic degradation pathways of lignocellulolytic biomass as well as the potential and current industrial applications of the involved fungal enzymes.

Dark fermentative hydrogen production from hydrolyzed sugar beet pulp improved by iron addition

This study evaluated the impact of three different iron compounds (Fe₂O₃, FeSO₄, FeCl₃) on hydrogen production via mesophilic dark fermentation (DF) of hydrolyzed sugar beet pulp (SBP). In batch tests, the maximum hydrogen yield of over 200 dm³H₂/kgVS was achieved with the addition of 0.1 gFe₂O₃/dm³, which was twice greater than the control. In semi-continuous experiments, the highest hydrogen production of 52.11 dm³H₂/kgVS combined with 19.4 dm³CH₄/kgVS methane yield was obtained at a dose of 1 gFe₂O₃/dm³. Acetic, lactic and caproic acids were the main metabolic products of DF. Microbiological studies showed some balance between hydrogen producing microorganisms from the order Clostridiales and lactic acid producers (LAB) affiliated with the orders Lactobacillales and Coriobacteriales. Moreover, the presence of methanogens affiliated to the genera Methanobrevibacter and Methanosphaera was also documented. An interesting finding was the appearance of rare bacteria from the genus Caproiciproducens, which was responsible for increased caproic acid production.

State of the art of straw treatment technology: Challenges and solutions forward

Straw as an agricultural byproduct has been recognized as a potential resource. However, open-field straw burning is still the main mean in many regions of the world, which causes the wasting of resource and air pollution. Recently, many technologies have been developed for energy and resource recovery from straw, of which the biological approach has attracted growing interests because of its economically viable and eco-friendly nature. However, pretreatment of straw prior to biological processes is essential, and largely determines the process feasibility, economic viability and environmental sustainability. Thus, this review attempts to offer a critical and holistic analysis of current straw pretreatment technologies and management practices. Specifically, an integrated biological processes coupled with microbial degradation and enzymatic hydrolysis was proposed, and its potential benefits, limitations and challenges associated with future large-scale straw treatment were also elaborated, together with the perspectives and directions forward.

Enhancement of anaerobic digestion of phoenix tree leaf by mild alkali pretreatment: Optimization by Taguchi orthogonal design and semi-continuous operation

This study aimed at evaluating the valorization of a typical yard waste, phoenix tree leaf (PTL), through mild alkali pretreatment followed by anaerobic digestion (AD). To this end, L₉ Taguchi orthogonal biochemical methane potential (BMP) tests and semi-continuous AD experiments were conducted to examine the optimum pretreatment condition and the long term effect of alkali pretreatment on AD. The community structure evolutions were analyzed by high throughput 16S rRNA gene pyrosequencing. The results indicated that alkali pretreatment was effective on decrystallization and releasing more surface of PTL for enzyme attacking. The methane yield was positively correlated with lignin removal (R²=0.8242). In semi-continuous mode, 151.5±7.9 mL/g VS of the methane yield was obtained for alkali pretreated PTL, which was 80% higher than that of untreated one. Microbial community analysis indicated that alkali pretreatment led to a higher abundance of dominated bacteria (Bacteroidetes and Clostridia) and archaea of Methanosaeta.

Properties of Polyvinyl Alcohol Films Composited With Hemicellulose and Nanocellulose Extracted From Artemisia selengensis Straw

Artemisia selengensis straw is an agricultural residue with great potential as a renewable resource because it is rich in lignocellulose. In this study, A. selengensis straw was used as a source of hemicelluloses (ASH) and cellulose nanocrystals (ASCNC) to produce biodegradable films. Different content levels of ASCNC were used as additives to improve composite films with ASH and polyvinyl alcohol (PVA). Various mechanical and hydrophobic properties of the films were analyzed. The composite films enhanced by ASCNC exhibited greater strength and were more effective as a barrier to water vapor when compared to that of the control ASH/PVA film. The tensile strength of the composite film was increased 80.1% to 36.21 MPa with ASCNC loading exceeding 9%, and the water vapor transmission rate decreased 15.45% when 12% ASCNC was added. Furthermore, the ASCNC-enhanced ASH/PVA composite film reduced a greater amount of light transmission than the control film.

In Vitro Evaluation of Enriched Brewers' Spent Grains Using Bacillus subtilis WX-17 as Potential Functional Food Ingredients

Brewers' spent grains (BSGs) are nutritious food processing by-products generated in the brewing industry. In this study, in vitro digestion-fermentation was employed to examine fermented BSG using Bacillus subtilis WX-17 as functional food ingredients. Insoluble fibers in BSG were converted into soluble fibers after fermentation, giving an increase from 6.13 ± 0.42 to 9.37 ± 0.53 mg/100 g BSG. After in vitro digestion of unfermented and fermented BSG, various nutritional components were found to be higher in fermented BSG. Components such as amino acids and fatty acids gave a concentration of 1.635 ± 0.236 mg/mL and 6.35 ± 0.65 mg/mL, respectively. Additionally, vitamin K₂ MK7 was detected in fermented BSG with a concentration of 0.00012 ± 0.000005 mg/mL. Probiotics Bacillus subtilis WX-17 was observed to withstand the in vitro digestion. After in vitro fermentation, various short-chain fatty acids namely acetic acid, propanoic acid, and butyric acid were produced at higher amounts for fermented BSG. The concentrations obtained were 124.11 ± 18.72 mM, 13.18 ± 1.38 mM, and 46.25 ± 7.57 mM respectively. As for gut microbiota profile, differential genera such as Bacteroides and Ruminococcus were detected, showing different effects on the intestinal microbiota. This study demonstrates the potential of using microbial fermentation of underutilized BSG to serve as potential functional food ingredients.

Microorganisms and Enzymes Used in the Biological Pretreatment of the Substrate to Enhance Biogas Production: A Review

The pretreatment of lignocellulosic biomass (LC biomass) prior to the anaerobic digestion (AD) process is a mandatory step to improve feedstock biodegradability and biogas production. An important potential is provided by lignocellulosic materials since lignocellulose represents a major source for biogas production, thus contributing to the environmental sustainability. The main limitation of LC biomass for use is its resistant structure. Lately, biological pretreatment (BP) gained popularity because they are eco-friendly methods that do not require chemical or energy input. A large number of bacteria and fungi possess great ability to convert high molecular weight compounds from the substrate into lower mass compounds due to the synthesis of microbial extracellular enzymes. Microbial strains isolated from various sources are used singly or in combination to break down the recalcitrant polymeric structures and thus increase biogasgeneration. Enzymatic treatment of LC biomass depends mainly on enzymes like hemicellulases and cellulases generated by microorganisms. The articles main purpose is to provide an overview regarding the enzymatic/biological pretreatment as one of the most potent techniques for enhancing biogas production.

Transgenic Poplar Designed for Biofuels

Members of the genus Populus (i.e., cottonwood, hybrid poplar) represent a promising source of lignocellulosic biomass for biofuels. However, one of the major factors negatively affecting poplar's efficient conversion to biofuel is the inherent recalcitrance to enzymatic saccharification due to cell wall components such as lignin. To this effect, there have been efforts to modify gene expression to reduce biomass recalcitrance by changing cell wall properties. Here, we review recent genetic modifications of poplar that led to change cell wall properties and the resulting effects on subsequent pretreatment efficacy and saccharification. Although genetic engineering's impacts on cell wall properties are not fully predictable, recent studies have shown promising improvement in the biological conversion of transgenic poplar to biofuels.

Chemoenzymatic conversion of Sorghum durra stalk into furoic acid by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis

In this study, chemoenzymatic conversion of Sorghum durra stalk (SDS) into furoic acid was developed by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis method. Dry dewaxed SDS (75 g/L) was catalyzed into furfural at 57.8% yield with heterogeneous Sn-argil (2.0 wt% dosage) in n-ethyl butyrate-H₂O (1:1, v:v) biphasic system using a microwave (600 W) for 10 min at 180 °C. In this biphasic media (pH 6.5), SDS-derived furfural (125.0 mM) was biologically oxidized to furoic acid by immobilized Brevibacterium lutescens cells harboring furfural-oxidizing activity at 30 °C, and furfural was wholly transformed to furoic acid within 24 h. Finally, the recovery and reuse of the Sn-argil catalyst and immobilized biocatalysts were conducted for synthesizing furoic acid from SDS in the biphasic system. This chemoenzymatic route can be attractive for furoic acid production.

Pretreatment of Grape Stalks by Fungi: Effect on Bioactive Compounds, Fiber Composition, Saccharification Kinetics and Monosaccharides Ratio

Grape stalks, an inedible lignocellulosic residue from winemaking and agro-industrial grape juice production, can be valorized as a source of bioactive compounds and as feedstock for the saccharification and bioconversion of soluble sugars. Solid-state fermentation (SSF) by six white-rot fungi was applied as pretreatment. Fiber composition, free radical scavenging activity, four ligninolytic, and three hydrolytic enzyme activities were determined. Saccharification kinetics, yield, and productivity were evaluated and complemented with scanning electron microscopy (SEM), high performance liquid chromatography (HPLC) quantification of monosaccharides, and principal component analysis (PCA). After SSF, the biomass exhibited a drastic free radical scavenging activity decrease and the main enzymes produced were manganese-dependent peroxidase and xylanase. Scanning electron microscopy revealed the erosion of cell walls, and PCA exhibited a negative correlation between saccharification, and neutral detergent fiber and acid detergent lignin. Phlebia rufa pretreated biomass gave the highest sugars yield and productivity, representing a nearly three-fold increase compared to untreated samples. Also, monosaccharides quantification revealed that the 1:1 ratio of glucose to the sum of xylose plus galactose changes to the value of 2:1 after pretreatment. In this work, and for the first time, P. rufa proved to be an effective pretreatment of grape stalks for the saccharification and further bioconversion into value-added chemicals. In addition, lignocellulolytic enzymes were also produced through SSF.

Enzymatic Hydrolysis of Sugarcane Bagasse in Aqueous Two-Phase Systems (ATPS): Exploration and Conceptual Process Design

The enzymatic conversion of lignocellulosic material to sugars can provide a carbon source for the production of energy (fuels) and a wide range of renewable products. However, the efficiency of this conversion is impaired due to product (sugar) inhibition. Even though several studies investigate how to overcome this challenge, concepts on the process to conduct the hydrolysis are still scarce in literature. Aqueous two-phase systems (ATPS) can be applied to design an extractive reaction due to their capacity to partition solutes to different phases in such a system. This work presents strategies on how to conduct extractive enzymatic hydrolysis in ATPS and how to explore the experimental results in order to design a feasible process. While only a limited number of ATPS was explored, the methods and strategies described could easily be applied to any further ATPS to be explored. We studied two promising ATPS as a subset of a previously high throughput screened large set of ATPS, providing two configurations of processes having the reaction in either the top phase or in the bottom phase. Enzymatic hydrolysis in these ATPS was performed to evaluate the partitioning of the substrate and the influence of solute partitioning on conversion. Because ATPS are able to partition inhibitors (sugar) between the phases, the conversion rate can be maintained. However, phase forming components should be selected to preserve the enzymatic activity. The experimental results presented here contribute to a feasible ATPS-based conceptual process design for the enzymatic conversion of lignocellulosic material.

Newly identified genes contribute to vanillin tolerance in Saccharomyces cerevisiae

Exploring the mechanisms of tolerance in microorganisms to vanillin, which is derived from lignin, will benefit the design of robust cell factories that produce biofuels and chemicals using lignocellulosic materials. Our objective was to identify the genes related to vanillin tolerance in Saccharomyces cerevisiae. We investigated the effects on vanillin tolerance of several genes that have site mutations in the highly vanillin‐tolerant strain EMV‐8 compared to its parental line NAN‐27. The results showed that overexpression of GCY1, a gene that encodes an aldo‐keto reductase that also has mRNA‐binding activity, YPR1, a paralog of GCY1 that encodes an aldo‐keto reductase, PEX5, a gene that encodes a peroxisomal membrane signal receptor and MBF1, a gene that encodes a multiprotein bridging factor increase the specific growth rates (μ) by 49%, 41%, 44% and 48 %, respectively, in medium containing 6 mmol l⁻¹ vanillin. Among these gene products, Gcy1p and Ypr1p showed NADPH‐dependent and NAD(P)H‐dependent vanillin reductase activity, respectively. The reductase‐inactive mutant Gcy1p^Y56F also increased vanillin tolerance in S. cerevisiae, suggesting that other mechanisms exist. Although TRS85 and PEX5, genes for which the mRNAs are binding targets of Gcy1p, were shown to be related to vanillin tolerance, both the mRNA and protein levels of these genes were not changed by overexpression of GCY1. The relationship between the mRNA‐binding activity of Gcy1p and its positive effect on vanillin tolerance is still not clear. Finally, we found that the point mutation D112A in Mbf1p, which disrupts the binding of Mbf1p and the TATA element‐binding protein (TBP), did not decrease the positive effect of Mbf1p on vanillin tolerance. This indicates that the binding of Mbf1p and TBP is not necessary for the positive effect on vanillin tolerance mediated by Mbf1p. We have successfully identified new genes related to vanillin tolerance and provided novel targets that can be used to improve the vanillin tolerance of S. cerevisiae. Moreover, we have extended our understanding of the proteins encoded by these genes.

Bioconversion of bamboo shoot shell to methane assisted by microwave irradiation and fungus metabolism

Bamboo shoot shell (BSS), a major byproduct from bamboo shoot industries with a high amount of output annually, needs to be sustainably management due to its impact on environment and human health. Anaerobic digestion is an eco-friendly and sustainable option, but its efficiency is limited by recalcitrance of lignocellulose structure. A cascade pretreatment (CP) using microwave irradiation and fungus metabolism was developed in this work to reduce the recalcitrance of BSS and enhance its methane production. The results showed significant synergistic effects of microwave irradiation and fungus metabolism on anaerobic digestion of BBS. The methane yield by CP increased by 162.9% (reached to 223.4 mL/g VS) when compared to control group. This was higher than both the values of fungal pretreatment (101.0 mL/g VS, 18.9% increase), and microwave pretreatment (110.5 mL/g VS, 30.1% increase) alone. Further mechanisms of the synergistic effects were revealed. Microwave irradiation provided dissolved products and more accessible BBS for fungus action. In particular, the GC-MS analysis indicated the dissolved products induced fungal laccase activity effectively, and the highest activity in CP was 1.91-fold higher than that in fungal pretreatment alone. The fungus in cascade process further increased accessible surface area and reducing sugars (20.2-43.2%, which compared to fungal pretreatment alone), and reduced significantly the lignin content (42.2-49.1%) and crystallinity (4.5-8.1%) of BSS.

Global Transcriptomic Responses of Roseithermus sacchariphilus Strain RA in Media Supplemented with Beechwood Xylan

The majority of the members in order Rhodothermales are underexplored prokaryotic extremophiles. Roseithermus, a new genus within Rhodothermales, was first described in 2019. Roseithermus sacchariphilus is the only species in this genus. The current report aims to evaluate the transcriptomic responses of R. sacchariphilus strain RA when cultivated on beechwood xylan. Strain RA doubled its growth in Marine Broth (MB) containing xylan compared to Marine Broth (MB) alone. Strain RA harbors 54 potential glycosyl hydrolases (GHs) that are affiliated with 30 families, including cellulases (families GH 3, 5, 9, and 44) and hemicellulases (GH 2, 10, 16, 29, 31,43, 51, 53, 67, 78, 92, 106, 113, 130, and 154). The majority of these GHs were upregulated when the cells were grown in MB containing xylan medium and enzymatic activities for xylanase, endoglucanase, β-xylosidase, and β-glucosidase were elevated. Interestingly, with the introduction of xylan, five out of six cellulolytic genes were upregulated. Furthermore, approximately 1122 genes equivalent to one-third of the total genes for strain RA were upregulated. These upregulated genes were mostly involved in transportation, chemotaxis, and membrane components synthesis.

Isolation of Clostridium from Yunnan-Tibet hot springs and description of Clostridium thermarum sp. nov. with lignocellulosic ethanol production

Lignocellulose is considered a major source of renewable energy that serve as an alternative to the fossil fuels. Members of the genus Clostridium are some of the many microorganisms that have the ability to degrade lignocellulose efficiently to sugar, which can be further converted to biofuel. In this study, we isolated twelve Clostridium strains from hot spring samples of Yunnan and Tibet, of which isolates SYSU GA15002^T and SYSU GA17076 showed low 16S rRNA gene sequence identity profiles to any of the validly named Clostridium strains (<94.0%). Studies using a polyphasic taxonomy approach concluded that the two isolates represent one novel species of the genus Clostridium, for which we propose the name Clostridium thermarum sp. nov., with SYSU GA15002^T as the type strain of the species. Isolate SYSU GA15002^T has an optimum growth temperature at 45°C. Fermentation of the substrates cellobiose, cellulose, xylan and untreated straw powder by this strain results in the production of ethanol, along with acetate and formate. The complete pathways for the conversion of cellulose and xylan to ethanol is also predicted from the genome of isolate SYSU GA15002^T, which revealed a single step conversion of lignocellulosic biomass through consolidated bioprocessing. This paper is a comprehensive study encompassing isolation, polyphasic taxonomy, lignocellulose biodegradation and the genomic information of Clostridium in Yunnan-Tibet hot springs.

Technology innovations for food security in Singapore: A case study of future food systems for an increasingly natural resource-scarce world

Background

Food security is becoming an increasingly important global issue. Anthropogenic factors such as rapid urbanization and industrialization have strained finite resources like land and water. Therefore, against the impending threat of food security, the world can no longer rely on traditional methods to meet its needs. Instead, more creative and technologically advanced methods must be adopted to maximise diminishing natural resources. Singapore is a good case study of a small city-state that is trying to increase its own self-production of food using technology.

Scope and approach

This review highlights the technologies that Singapore have adopted in enhancing food security given its limitation in natural resources. These methodologies serve as a case study that can be used as a reference point in light of the increasingly finite natural resources. The review also presents the advantages of these techniques as well as challenges that need to be overcome for them to be more widely adopted.

Key findings and conclusion

To increase self-production of food and enhance its food security, Singapore has employed the use of technologies such as vertical farming and aquaponics in urban farming, nutrient recovery from food waste, biodegradable food packaging from durian rinds, natural preservatives, insect farming, microalgae and cultivated meat as alternative protein sources. These technologies workaround Singapore's land and natural resource constraints, which many countries around the world can adapt. However, many of them are still relatively nascent with numerous challenges, which have to be addressed before they can be widely accepted and implemented.

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Long term agriculture and pollution have led to depletion of natural resources.

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Technology innovations can be used to mitigate natural resource constraints.

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Singapore has adopted numerous technologies to enhance food security.

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Areas include urban farming, processing technology and alternative food sources.

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Singapore's model provides a good example to increase self-production of food.

New insights into two yeast BDHs from the PDH subfamily as aldehyde reductases in context of detoxification of lignocellulosic aldehyde inhibitors

At least 24 aldehyde reductases from Saccharomyces cerevisiae have been characterized and most function in in situ detoxification of lignocellulosic aldehyde inhibitors, but none is classified into the polyol dehydrogenase (PDH) subfamily of the medium-chain dehydrogenase/reductase (MDR) superfamily. This study confirmed that two (2R,3R)-2,3-butanediol dehydrogenases (BDHs) from industrial (denoted Y)/laboratory (denoted B) strains of S. cerevisiae, Bdh1p(Y)/Bdh1p(B) and Bdh2p(Y)/Bdh2p(B), were members of the PDH subfamily with an NAD(P)H binding domain and a catalytic zinc binding domain, and exhibited reductive activities towards lignocellulosic aldehyde inhibitors, such as acetaldehyde, glycolaldehyde, and furfural. Especially, the highest enzyme activity towards acetaldehyde by Bdh2p(Y) was 117.95 U/mg with cofactor nicotinamide adenine dinucleotide reduced (NADH). Based on the comparative kinetic property analysis, Bdh2p(Y)/Bdh2p(B) possessed higher specific activity, substrate affinity, and catalytic efficiency towards glycolaldehyde than Bdh1p(Y)/Bdh1p(B). This was speculated to be related to their 49% sequence differences and five nonsynonymous substitutions (Ser41Thr, Glu173Gln, Ile270Leu, Ile316Met, and Gly317Cys) occurred in their conserved NAD(P)H binding domains. Compared with BDHs from a laboratory strain, Bdh1p(Y) and Bdh2p(Y) from an industrial strain displayed five nonsynonymous mutations (Thr¹², Asn⁶¹, Glu¹⁶⁸, Val²²², and Ala²³⁵) and three nonsynonymous mutations (Ala³⁴, Ile⁹⁶, and Ala³⁶⁹), respectively. From a first analysis with selected aldehydes, their reductase activities were different from BDHs of laboratory strain, and their catalytic efficiency was higher towards glycolaldehyde and lower towards acetaldehyde. Comparative investigation of kinetic properties of BDHs from S. cerevisiae as aldehyde reductases provides a guideline for their practical applications in in situ detoxification of aldehyde inhibitors during lignocellulose bioconversion.Key Points• Two yeast BDHs have enzyme activities for reduction of aldehydes.• Overexpression of BDHs slightly improves yeast tolerance to acetaldehyde and glycolaldehyde.• Bdh1p and Bdh2p differ in enzyme kinetic properties.• BDHs from strains with different genetic backgrounds differ in enzyme kinetic properties.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.

Hyperthermophilic Treatment of Grass and Leaves to Produce Hydrogen, Methane and VFA-Rich Digestate: Preliminary Results

In this study, the feasibility of hydrogen and methane production from grass and leaves via hyperthermophilic anaerobic digestion was investigated. The hyperthermophilic treatment of grass at 70 °C resulted in the highest concentrations of volatile fatty acids (TVFA) and reducing sugars in the supernatant of over 21 and 6.5 g/L reported on day 3 and 4 of the experiment. In contrast, hydrolysis and acidification of leaves performed slower and with lower efficiency, as the peak concentrations of TVFA and reducing sugars were observed at the end of the process. However, the highest cumulative hydrogen and methane yields of 69.64 mLH2/gVS and 38.63 mLCH4/gVS were reported for leaves digested at 70 °C, whereas the corresponding maximum productions observed for grass were 50 mLH2/gVS and 1.98 mLCH4/gVS, respectively. A temperature increase to 80 °C hampered hydrogen and methane production and also resulted in lower yields of volatile fatty acids, reducing sugars and ammonia as compared to the corresponding values reported for 70 °C.

Recent developments in the application of kraft pulping alkaline chemicals for lignocellulosic pretreatment: Potential beneficiation of green liquor dregs waste

Lignocellulosic waste has offered a cost-effective and food security-wise substrate for the generation of biofuels and value-added products. However, its recalcitrant properties necessitate pretreatment. Of the various pretreatment methods, alkaline techniques have gained prominence as efficient catalysts. The kraft pulping industry represents a major hub for the generation of white, black and green liquor alkaline solutions during the paper making process. Despite its well-known significance in the kraft pulping process, green liquor (GL) has been widely applied for lignocellulosic pretreatment. Recently, green liquor dregs (GLD), an alkaline waste generated from the kraft pulping industry has piqued interest. Therefore, this review outlines the general flow of the kraft pulping process and the alkaline chemicals derived. In addition, the extensively studied GL for lignocellulosic pretreatment is discussed. Subsequently, the potential beneficiation of GLD for lignocellulosic pretreatment is presented. Furthermore, the challenges and prospects of lignocellulosic pretreatments are highlighted.

Biological treatment of lignocellulosic biomass by Curvularia lunata for biogas production

In the present study, biological treatment of lignocellulosic biomass has been performed by employing Curvularia lunata. Optimization of treatment conditions was performed by using response surface methodology to reduce the duration of treatment time. Three factors were studied at three severity levels: temperature - 28, 32, 36 °C; moisture content - 65, 75, 85%; treatment time - 14, 28, 42 days. Released reducing sugars were considered as the output response as the disruption of lignin barrier by biological treatment should increase the quantity of free reducing sugar. Impact of different combinations of factors (at varying severity levels) on output response was studied to attain the optimized conditions: 32 °C, 23 days and 65% moisture. Predicted outcomes were aligned with the experimental results (R2 = 0.93). After treating at optimized conditions, wheat and pearl millet straw were subjected to anaerobic digestion and showcased 19 and 28% increase in biogas production respectively as compared to the untreated straws.

Insight into understanding the performance of deep eutectic solvent pretreatment on improving enzymatic digestibility of bamboo residues

Deep eutectic solvent (DES) is a promising pretreatment for improving enzymatic digestibility of lignocellulosic material by altering the physicochemical properties. However, few work has been done to quantitatively analysis the physicochemical properties changes of lignocellulosic material with enzymatic digestibility. In this work, DES pretreatment with different molar ratios of choline chloride/lactic acid was carried out on bamboo residues and respective enzymatic digestibility was investigated and linearly fitted with corresponding physicochemical features changes of the pretreated bamboo residues. Results showed that enzymatic digestibility of DES-pretreated bamboo residues was enhanced with the increasing molar ratio of choline chloride/lactic acid, which was due to DES pretreatment's ability to remove lignin and xylan, reduce the degree of polymerization of cellulose, enhance the crystallite size of cellulose, and improve cellulose accessibility. Several compelling linear correlations (R2 = 0.6-0.9) were observable between enzymatic digestibility and these changes of physicochemical properties, demonstrating how DES pretreatment improve the enzymatic digestibility.

A Review of Biohydrogen Productions from Lignocellulosic Precursor via Dark Fermentation: Perspective on Hydrolysate Composition and Electron-Equivalent Balance

This paper reviews the current technological development of bio-hydrogen (BioH2) generation, focusing on using lignocellulosic feedstock via dark fermentation (DF). Using the collected reference reports as the training data set, supervised machine learning via the constructed artificial neuron networks (ANNs) imbedded with feed backward propagation and one cross-out validation approach was deployed to establish correlations between the carbon sources (glucose and xylose) together with the inhibitors (acetate and other inhibitors, such as furfural and aromatic compounds), hydrogen yield (HY), and hydrogen evolution rate (HER) from reported works. Through the statistical analysis, the concentrations variations of glucose (F-value = 0.0027) and acetate (F-value = 0.0028) were found to be statistically significant among the investigated parameters to HY and HER. Manipulating the ratio of glucose to acetate at an optimal range (approximate in 14:1) will effectively improve the BioH2 generation (HY and HER) regardless of microbial strains inoculated. Comparative studies were also carried out on the evolutions of electron equivalent balances using lignocellulosic biomass as substrates for BioH2 production across different reported works. The larger electron sinks in the acetate is found to be appreciably related to the higher HY and HER. To maintain a relative higher level of the BioH2 production, the biosynthesis needs to be kept over 30% in batch cultivation, while the biosynthesis can be kept at a low level (2%) in the continuous operation among the investigated reports. Among available solutions for the enhancement of BioH2 production, the selection of microbial strains with higher capacity in hydrogen productions is still one of the most phenomenal approaches in enhancing BioH2 production. Other process intensifications using continuous operation compounded with synergistic chemical additions could deliver additional enhancement for BioH2 productions during dark fermentation.

Using highly recyclable sodium caseinate to enhance lignocellulosic hydrolysis and cellulase recovery

Most additives that capable of enhancing enzymatic hydrolysis of lignocellulose are petroleum-based, which are not easy to recycle with poor biodegradability. In this work, highly recyclable and biodegradable sodium caseinate (SC) was used to enhance lignocellulosic hydrolysis with improved cellulase recyclability. When the pH decreased from 5.5 to 4.8, more than 96% SC could be precipitated from the solution and recovered. Adding SC increased enzymatic digestibility of dilute acid pretreated eucalyptus (Eu-DA) from 39.5% to 78.2% under Eu-DA loading of 10 wt% and pH = 5.5, and increase cellulase content in 72 h hydrolysate from only 15.2% of the original to 60.0%, which facilitated the recovery of cellulases through re-adsorption by fresh substrates. With multiple cycles of re-adsorption, application of SC not only increased the sugar yield of Eu-DA by 95.5%, but also reduced cellulase loading by 40%.

Effects of rice straw structure on chaetoglobosin A production by Chaetomium globosum CGMCC 6882

As the most abundant macromolecules in nature, lignocelluloses are served as a promising and renewable source for sustainable production of high value chemical compounds. In present work, extrusion pretreatment with 23% (w/w) distilled water, 2% (w/w) glycerol and 1 g/L NaHCO₃ as moisture agent, not only reduced the particle size, crystallinity and component contents (cellulose, hemicelluloses and lignin) of rice straw, but also effectively enhanced chaetoglobosin A yield and degradation rate of rice straw by C. globosum CGMCC 6882. Meanwhile, mycelial biomass of C. globosum CGMCC 6882 increased from 2.9 g/L to 7.0 g/L, mycelia growth time reduced by 2 days and chaetoglobosin A titer increased from 108.4 mg/L to 270.2 mg/L, representing an increase of 149.3%. Furthermore, degradation rate of rice straw by C. globosum CGMCC 6882 increased from 28.93% to 65.38%. This work provides a good guidance for production of chaetoglobosin A from lignocelluloses.

Conversion of waste cooking oil into biodiesel using heterogenous catalyst derived from cork biochar

In this study, a heterogeneous catalyst prepared by pyrolysis of waste cork (Quercus suber) was used for the transesterification of waste cooking oil (WCO). Physicochemical properties of the synthesized biochar catalyst were studied using BET, SEM, FTIR, and XRD. The experiment results demonstrate that heterogeneous catalyst synthesized at 600 °C showed maximum fatty acids methyl esters (FAMEs) conversion (98%) at alcohol:oil (25:1), catalyst loading (1.5% w/v) and temperature 65 °C. Biodiesel produced from WCO (Canola oil) mainly composed of FAMEs in following order C18:1 > C18:2 > C16:0 > C18:0 > C20:0. Properties of produced biodiesel were analysed as cetane number (CN) 50.56, higher heating value (HHV) 39.5, kinematic viscosity (ʋ) 3.9, and density (ρ) 0.87.

The critical role of lignin in lignocellulosic biomass conversion and recent pretreatment strategies: A comprehensive review

Heterogeneity and rigidity of lignocellulose causing resistance to its deconstruction have provided technical and economic challenges in the current biomass conversion processes. Lignin has been considered as a crucial recalcitrance component in biomass utilization. An in-depth understanding of lignin properties and their influences on biomass conversion can provide clues to improve biomass utilization. Also, utilization of lignin can significantly increase the economic viability of biorefinery. Recent lignin-targeting pretreatments have aimed not only to overcome recalcitrance for biomass conversion but also to selectively fractionate lignin for lignin valorization. Numerous studies have been conducted in biomass characteristics and conversion technologies, and the role of lignin is critical for lignin valorization and biomass pretreatment development. This review provides a comprehensive review of lignin-related biomass characteristics, the impact of lignin on the biological conversion of biomass, and recent lignin-targeting pretreatment strategies. The desired lignin properties in biorefinery and future pretreatment directions are also discussed.

Boosting landfill gas production from lignin-containing wastes via termite hindgut microorganism

Lignocellulose comprises a significant portion of municipal solid waste (MSW) - 40-70% in developed countries, including paper, wood, and yard waste. Cellulose and hemicellulose are often shielded by lignin, posing a barrier to waste decomposition and landfill gas generation. Unfortunately, lignin is resistant to microbial degradation under low-oxygen conditions that normally occur in MSW landfills. The bacterium strain TAV5, microaerophilic and member of phylum Verrucomicrobia, isolated from the hindgut of the Reticulitermes flavipes termite, the most widely distributed subterranean termite in North America. Its genome contains genes associated with methylotrophic competency which code for enzymes that structurally modify lignin. The overall goal of this research was to use TAV5 to modify lignin and boost methane production from MSW. Batch-scale reactors (125 mL) were filled with paper, yard, or wood waste, and four ratios of mixed of waste. Reactors were seeded with different ratios of TAV5 to anaerobic digester (AD) microorganisms (representing landfill anaerobic microorganisms). Based on batch tests, optimal ratios of TAV5 to AD microorganisms were used to seed wastes (mixed, yard, and wood) in 6-gallon reactors. Addition of TAV5 increased methane production from mixed waste, yard waste, and wood, by 49%, 34%, and 297%, respectively. TAV5 decreased acid soluble lignin by 7-39%, depending on waste type. TAV5 grown under aerobic conditions and room temperature (not requiring a heated anaerobic chamber) was found to remain viable and increase methane production under low-level oxygen conditions (1-2%). This finding will potentially lessen costs for growing large volumes of it for seeding landfills.

Purification and Biochemical Characterization of Alkalophilic Cellulase from the Symbiotic Bacillus subtilis BC1 of the Leopard Moth, Zeuzera pyrina (L.) (Lepidoptera: Cossidae)

In the current study, an extracellular cellulase belonging to symbiotic Bacillus subtilis Bc1 of the leopard moth is purified and characterized. The molecular mass of enzyme was 47.8 kDa using SDS-PAGE. The purified enzyme had optimum activity in temperature and pH around 60 °C and 8, respectively. The purified cellulase was introduced as a stable enzyme in a wide variety of temperature (20-80 °C) and pH (4-10) and remained active to more than 74% at 80 °C for 1 h. Moreover, the cellulase extremely was stabled in the presence of metal ions and organic solvents and its activity was increased by acetone (20% v/v), CaCl₂ and CoCl₂ and inhibited by MnCl₂ and NiCl₂. The values of enzyme's K_m and V_max were found to be 1.243 mg/mL and 271.3 µg/mL/min, respectively. The purified cellulase hydrolyzed cellulose, avicel and carboxymethyl cellulose (CMC) and the final product of CMC hydrolysis was cellobiose using thin-layer chromatography analysis. Consequently, owing to exo/endoglucanase activity and organic solvent, temperature and pH stability of the purified cellulase belong to B. subtilis BC1, it can be properly employed for various industrial purposes.

A critical review on current strategies and trends employed for removal of inhibitors and toxic materials generated during biomass pretreatment

The main objective of biomass pretreatment is to separate biomass components and provide easier access with ultimate aim for lignin removal, hemicellulose protection and cellulose crystallinity reduction. Effective bioconversion with least inhibitory compound production would play a considerable role in economic practicability of the process in order to achieve economic sustainability. In this regard, detoxification is an important condition to make biomass hydrolysate acquiescent to bioconversion; also, understanding of inhibitors effect on growth and fermentation are necessary requirements for system detoxification. A number of physical, chemical and biological methods like feedstock selection, membrane selection, neutralization, use of activated charcoal etc have been recommended and developed for removal or minimizing the inhibitory compounds effect. This work reviews various inhibitory compounds produced during pretreatment methods and their removal by various processes.

Pretreatment of polysaccharidic wastes with cellulolytic Aspergillus fumigatus for enhanced production of biohythane in a dual-stage process

Biological pretreatment of polysaccharidic wastes (PWs) is a cost-effective and environmentally friendly approach to improve the digestibility and utilization of these valuable substrates in dual-stage biohythane production. In order to reduce the prolonged incubation time and loss of carbohydrate during the pretreatment of PWs with Aspergillus fumigatus, a systematic optimization using Taguchi methodology resulted in an unprecedented recovery of soluble carbohydrates (362.84 mg g^-1) within 5 days. The disruption and fragmentation of lignocellulosic structures in PWs, and possible saccharification of cellulose and hemicellulose components, increased its digestibility. A dual-stage biohythane production with pretreated PWs showed increased yield (214.13 mL g^-1 VS_added), which was 56% higher than the corresponding value with the untreated PWs. This resulted in 47% higher energy recovery as biohythane in pretreated biomass compared to untreated biomass. Optimized fungal pretreatment is, therefore, an effective method to improve the digestibility of PWs and its subsequent conversion to biohythane.

Comparison of enzymatic saccharification and lignin structure of masson pine and poplar pretreated by p-Toluenesulfonic acid

p-Toluenesulfonic acid (p-TsOH) with the hydrotropic and recyclable properties is widely used for rapid remove of lignin from lignocelluloses at low temperature (<100 °C). In this work, both softwood masson pine and hardwood poplar were pretreated with p-TsOH under different conditions and then subjected to enzymatic hydrolysis to compare the effect of p-TsOH pretreatment on their saccharification and lignin structure. Results showed p-TsOH has sensitive selectivity to lignin structure during pretreatment. Around 95% of lignin in poplar can be dissolved at 80 °C within 30 min, while for masson pine, the delignification is only 50%. Following enzymatic hydrolysis with cellulase loading of 20 FPU/g-cellulose for 72 h, the highest sugar yield of pretreated poplar and masson pine is 92.13% and 29.46%, respectively, which indicates that p-TsOH pretreatment alone works well with hardwoods (poplar). Structural analysis of removed lignin implies that p-TsOH mainly results in the cleavage of β-aryl ether bonds of lignin side chains, and the aromatic structure of lignin keeps intact. p-TsOH pretreatment shows the key advantages of low cost and rapid delignification for highly enzymatic saccharification, and provides a promising and green pathway for the development of low cost and sustainable bio-based products for developing a bio-based economy.