Challenges of Biomass Utilization for Bioenergy in a Climate Change Scenario

Recombinant GH3 β-glucosidase stimulated by xylose and tolerant to furfural and 5-hydroxymethylfurfural obtained from Aspergillus nidulans

The β-glucosidase gene from Aspergillus nidulans FGSC A4 was cloned and overexpressed in the A. nidulans A773. The resulting purified β-glucosidase, named AnGH3, is a monomeric enzyme with a molecular weight of approximately 80 kDa, as confirmed by SDS-PAGE. Circular dichroism further validated its unique canonical barrel fold (β/α), a feature also observed in the 3D homology model of AnGH3. The most striking aspect of this recombinant enzyme is its robustness, as it retained 100% activity after 24 h of incubation at 45 and 50 ºC and pH 6.0. Even at 55 °C, it maintained 72% of its enzymatic activity after 6 h of incubation at the same pH. The kinetic parameters Vmax, KM, and Kcat/KM for ρ-nitrophenyl-β-D-glucopyranoside (ρNPG) and cellobiose were also determined. Using ρNPG, the enzyme demonstrated a Vmax of 212 U mg - 1, KM of 0.0607 mmol L - 1, and Kcat/KM of 4521 mmol L - 1 s - 1 when incubated at pH 6.0 and 65 °C. The KM, Vmax, and Kcat/KM using cellobiose were 2.7 mmol L - 1, 57 U mg - 1, and 27 mmol -1 s - 1, respectively. AnGH3 activity was significantly enhanced by xylose and ethanol at concentrations up to 1.5 mol L - 1 and 25%, respectively. Even in challenging conditions, at 65 °C and pH 6.0, the enzyme maintained its activity, retaining 100% and 70% of its initial activity in the presence of 200 mmol L - 1 furfural and 5-hydroxymethylfurfural (HMF), respectively. The potential of this enzyme was further demonstrated by its application in the saccharification of the forage grass Panicum maximum, where it led to a 48% increase in glucose release after 24 h. These unique characteristics, including high catalytic performance, good thermal stability in hydrolysis temperature, and tolerance to elevated concentrations of ethanol, D-xylose, furfural, and HMF, position this recombinant enzyme as a promising tool in the hydrolysis of lignocellulosic biomass as part of an efficient multi-enzyme cocktail, thereby opening new avenues in the field of biotechnology and enzymology.

Microenzymes: Is There Anybody Out There?

Biological macromolecules are found in different shapes and sizes. Among these, enzymes catalyze biochemical reactions and are essential in all organisms, but is there a limit size for them to function properly? Large enzymes such as catalases have hundreds of kDa and are formed by multiple subunits, whereas most enzymes are smaller, with molecular weights of 20-60 kDa. Enzymes smaller than 10 kDa could be called microenzymes and the present literature review brings together evidence of their occurrence in nature. Additionally, bioactive peptides could be a natural source for novel microenzymes hidden in larger peptides and molecular downsizing could be useful to engineer artificial enzymes with low molecular weight improving their stability and heterologous expression. An integrative approach is crucial to discover and determine the amino acid sequences of novel microenzymes, together with their genomic identification and their biochemical biological and evolutionary functions.

Unveiling malic acid biorefinery: Comprehensive insights into feedstocks, microbial strains, and metabolic pathways

The over-reliance on fossil fuels and resultant environmental issues necessitate sustainable alternatives. Microbial fermentation of biomass for malic acid production offers a viable, eco-friendly solution, enhancing resource efficiency and minimizing ecological damage. This review covers three core aspects of malic acid biorefining: feedstocks, microbial strains, and metabolic pathways. It emphasizes the significance of utilizing biomass sugars, including the co-fermentation of different sugar types to improve feedstock efficiency. The review discusses microbial strains for malic acid fermentation, addressing challenges related to by-products from biomass breakdown and strategies for overcoming them. It delves into the crucial pathways and enzymes for malic acid production, outlining methods to optimize its metabolism, focusing on enzyme regulation, energy balance, and yield enhancement. These insights contribute to advancing the field of consolidated bioprocessing in malic acid biorefining.

A systematic review of the design considerations for the operation and maintenance of small-scale biogas digesters

This review investigates small-scale biogas digesters' design and construction considerations to address biogas digesters' failures shortly after installation. The frequent failures of small-scale or household biogas digesters negatively affect its adoption as a clean domestic cooking fuel in developing countries, affecting the achievement of Sustainable Development Goal (SDG) 7. The study considered Scopus database-indexed peer-reviewed journals published between 2000 and 2022. Selected papers focussed on real-time monitoring, stirring mechanisms, and temperature control systems based on predefined inclusion and exclusion criteria with initial search results of 4751 documents, narrowing to 55 papers. The PRISMA 2020 statement was adopted to conduct the study. The study highlights the importance of incorporating a real-time monitoring system as a design factor in small-scale biogas digesters for successful operation and maintenance. The study's findings may be helpful to practitioners, policymakers, and researchers promoting sustainable energy and waste management solutions in low-resource settings.

Thermochemical behavior of agricultural and industrial sugarcane residues for bioenergy applications

The Colombian sugarcane industry yields significant residues, categorized as agricultural and industrial. While bagasse, a widely studied industrial residue, is employed for energy recovery through combustion, agricultural residues are often left in fields. This study assesses the combustion behavior of these residues in typical collection scenarios. Additionally, it encompasses the characterization of residues from genetically modified sugarcane varieties in Colombia, potentially exhibiting distinct properties not previously documented. Non-isothermal thermogravimetrical analysis was employed to study the thermal behavior of sugarcane industrial residues (bagasse and pith) alongside agricultural residues from two different sugarcane varieties. This facilitated the determination of combustion reactivity through characteristic combustion process temperatures and technical parameters like ignition and combustion indexes. Proximate, elemental, and biochemical analyses revealed slight compositional differences. Agricultural residues demonstrated higher ash content (up to 34%) due to foreign matter adhering during harvesting, as well as soil and mud attachment during collection. Lignin content also varied, being lower for bagasse and pith, attributed to the juice extraction and milling processes that remove soluble lignin. Thermogravimetric analysis unveiled a two-stage burning process in all samples: devolatilization and char formation (~170°C), followed by char combustion (~310°C). Characteristic temperatures displayed subtle differences, with agricultural residues exhibiting lower temperatures and decomposition rates, resulting in reduced ignition and combustion indexes. This indicates heightened combustion reactivity in industrial residues, attributed to their elevated oxygen percentage, leading to more reactive functional groups and greater combustion stability compared to agricultural residues. This information is pertinent for optimizing sugarcane residues utilization in energy applications.

Meta-analysis of the responses of tree and herb to elevated CO2 in Brazil

The CO2 concentration has increased in the atmosphere due to fossil fuel consumption, deforestation, and land-use changes. Brazil represents one of the primary sources of food on the planet and is also the world's largest tropical rainforest, one of the hot spots of biodiversity in the world. In this work, a meta-analysis was conducted to compare several CO2 Brazilian experiments displaying the diversity of plant responses according to life habits, such as trees (79% natives and 21% cultivated) and herbs (33% natives and 67% cultivated). We found that trees and herbs display different responses. The young trees tend to allocate carbon from increased photosynthetic rates and lower respiration in the dark-to organ development, increasing leaves, roots, and stem biomasses. In addition, more starch is accumulated in the young trees, denoting a fine control of carbon metabolism through carbohydrate storage. Herbs increased drastically in water use efficiency, controlled by stomatal conductance, with more soluble sugars, probably with a transient accumulation of carbon primarily stored in seeds as a response to elevated CO2.

Trichoderma longibrachiatum and thermothelomyces thermophilus co-culture: improvement the saccharification profile of different sugarcane bagasse varieties

OBJECTIVES

The aim of the present work was to perform the co-culture between Trichoderma longibrachiatum LMBC 172, a mesophilic fungus, with Thermothelomyces thermophilus LMBC 162, a thermophilic fungus, by submerged fermentation in a bioreactor.

RESULTS

There was an increase in protein production, reaching the value of 35.60 ± 3.76 µg/ml at 72 h. An increase in the amount of proteins of 27.5% in relation to the isolated cultivation of T. longibrachiatum and 19.7% in comparison when T. thermophilus was isolated and cultivated. After that, the saccharification profile of three varieties of sugarcane (sugarcane in natura, culms of sugarcane SP80-3280, and culms of Energy cane) submitted in two pretreatments (autohydrolysis and chemical) was performed. The (e) chemical pretreatment was the better in generating of fermentable sugars from sugarcane bagasse and culms of Energy cane, while with the autohydrolysis pretreatment was obtained the better values to culms of SP80-3280 sugarcane. The sugars found were glucose, xylose, arabinose, and cellobiose.

CONCLUSION

These results suggest that the co-culture between these microorganisms has the potential to produce an enzymatic cocktail with high performance in the hydrolysis of materials from the sugar-alcohol industry.

Implications of preferential access to land and clean energy for sustainable aviation fuels

Aviation is highly dependent on liquid fossil fuel, and the production of 'sustainable aviation fuels' (SAF) is being proposed as a solution to removing the fossil carbon component, especially for long-haul flights. An analysis of 12 aviation roadmaps for net zero 2050 reveals heavy reliance on biogenic SAF in the medium-term and synthetic e-kerosene in the longer term. Realising these roadmaps could require 9 % of global renewable electricity and 30 % of sustainably available biomass in 2050, with significant energy 'losses'. The continued use of hydrocarbon fuel in the roadmaps generates 1.35 GtCO₂ in 2050, of which 30 % are still from fossil fuel. The net carbon savings from the 70 % depend on the direct and indirect life cycle emissions of producing SAF. Additional effects that are omitted in most roadmaps relate to decadal time lags in re-sequestering biocarbon in the case of forest biomass and the impact of non-CO₂ emissions. Both require greater scrutiny in fully understanding the climate impact of SAF substitution. The scaling up of SAF to not only maintain but grow global aviation is problematic as it competes for land needed for nature-based carbon removal, clean energy that could more effectively decarbonise other sectors, and captured CO₂ to be stored permanently. As such, SAF production undermines global goals of limiting warming to 1.5°; a conflict that is neither recognised in the roadmaps nor in the public debate.

Importance of incorporating spatial and temporal variability of biomass yield and quality in bioenergy supply chain

Biofuels made from biomass and waste residues will largely contribute to United States' 2050 decarbonization goal in the aviation sector. While cellulosic biofuels have the potential fuel performance equivalent to petroleum-based jet fuel, the biofuel industry needs to overcome the supply chain barrier caused by temporal and spatial variability of biomass yield and quality. This study highlights the importance of incorporating spatial and temporal variability during biomass supply chain planning via optimization modeling that incorporates 10 years of drought index data, a primary factor contributing to yield and quality variability. The results imply that the cost of delivering biomass to biorefinery may be significantly underestimated if the multi-year temporal and spatial variation in biomass yield and quality is not captured. For long term sustainable biorefinery operations, the industry should optimize supply chain strategy by studying the variability of yield and quality of biomass in their supply sheds.

Biochemical Characterization of an Endoglucanase GH7 from Thermophile Thermothielavioides terrestris Expressed on Aspergillus nidulans

Endoglucanases (EC 3.2.1.4) are important enzymes involved in the hydrolysis of cellulose, acting randomly in the β-1,4-glycosidic bonds present in the amorphous regions of the polysaccharide chain. These biocatalysts have been classified into 14 glycosyl hydrolase (GH) families. The GH7 family is of particular interest since it may act on a broad range of substrates, including cellulose, β-glucan, and xylan, an attractive feature for biotechnological applications, especially in the renewable energy field. In the current work, a gene from the thermophilic fungus Thermothielavioides terrestris, encoding an endoglucanase GH7 (TtCel7B), was cloned in the secretion vector pEXPYR and transformed into the high-protein-producing strain Aspergillus nidulans A773. Purified TtCel7B has a molecular weight of approximately 66 kDa, evidenced by SDS-PAGE. Circular dichroism confirmed the high β-strand content consistent with the canonical GH7 family β-jellyroll fold, also observed in the 3D homology model of TtCel7B. Biochemical characterization assays showed that TtCel7B was active over a wide range of pH values (3.5–7.0) and temperatures (45–70 °C), with the highest activity at pH 4.0 and 65 °C. TtCel7B also was stable over a wide range of pH values (3.5–9.0), maintaining more than 80% of its activity after 24 h. The KM and Vmax values in low-viscosity carboxymethylcellulose were 9.3 mg mL−1 and 2.5 × 104 U mg−1, respectively. The results obtained in this work provide a basis for the development of applications of recombinant TtCel7B in the renewable energy field.

Adjustments in photosynthetic pigments, PS II photochemistry and photoprotection in a tropical C4 forage plant exposed to warming and elevated [CO2]

Global climate change will impact crops and grasslands, affecting growth and yield. However, is not clear how the combination of warming and increased atmospheric carbon dioxide concentrations ([CO₂]) will affect the photosystem II (PSII) photochemistry and the photosynthetic tissue photoinhibition and photoprotection on tropical forages. Here, we evaluated the effects of elevated [CO₂] (∼600 μmol mol^-1) and warming (+2 °C increase temperature) on the photochemistry of photosystem II and the photoprotection strategies of a tropical C4 forage Panicum maximum Jacq. grown in a Trop-T-FACE facility under well-watered conditions without nutrient limitation. Analysis of the maximum photochemical efficiency of PSII (F_v/F_m), the effective PSII quantum yield Y(II), the quantum yield of regulated energy dissipation Y(NPQ), the quantum yield of non-regulated energy dissipation Y(NO), and the malondialdehyde (MDA) contents in leaves revealed that the photosynthetic apparatus of plants did not suffer photoinhibitory damage, and plants did not increase lipid peroxidation in response to warming and [CO₂] enrichment. Plants under warming treatment showed a 12% higher chlorophyll contents and a 58% decrease in α-tocopherol contents. In contrast, carotenoid composition (zeaxanthin and β-carotene) and ascorbate levels were not altered by elevated [CO₂] and warming. The elevated temperature increased both net photosynthesis rate and aboveground biomass but elevated [CO₂] increased only net photosynthesis. Adjustments in chlorophyll, de-epoxidation state of the xanthophylls cycle, and tocopherol contents suggest leaves of P. maximum can acclimate to 2 °C warmer temperature and elevated [CO₂] when plants are grown with enough water and nutrients during tropical autumn-winter season.

From source to sink: mechanistic insight of photoassimilates synthesis and partitioning under high temperature and elevated [CO2]

Photosynthesis is the vital metabolism of the plant affected by abiotic stress such as high temperature and elevated [CO₂] levels, which ultimately affect the source-sink relationship. Triose phosphate, the primary precursor of carbohydrate (starch and sucrose) synthesis in the plant, depends on environmental cues. The synthesis of starch in the chloroplasts of leaves (during the day), the transport of photoassimilates (sucrose) from source to sink, the loading and unloading of photoassimilates, and the accumulation of starch in the sink tissue all require a highly regulated network and communication system within the plant. These processes might be affected by high-temperature stress and elevated [CO₂] conditions. Generally, elevated [CO₂] levels enhance plant growth, photosynthetic rate, starch synthesis, and accumulation, ultimately diluting the nutrient of sink tissues. On the contrary, high-temperature stress is detrimental to plant development affecting photosynthesis, starch synthesis, sucrose synthesis and transport, and photoassimilate accumulation in sink tissues. Moreover, these environmental conditions also negatively impact the quality attributes such as grain/tuber quality, cooking quality, nutritional status in the edible parts and organoleptic traits. In this review, we have attempted to provide an insight into the source-sink relationship and the sugar metabolites synthesized and utilized by the plant under elevated [CO₂] and high-temperature stress. This review will help future researchers comprehend the source-sink process for crop growth under changing climate scenarios.

Immobilization and Application of the Recombinant Xylanase GH10 of Malbranchea pulchella in the Production of Xylooligosaccharides from Hydrothermal Liquor of the Eucalyptus (Eucalyptus grandis) Wood Chips

Xylooligosaccharides (XOS) are widely used in the food industry as prebiotic components. XOS with high purity are required for practical prebiotic function and other biological benefits, such as antioxidant and inflammatory properties. In this work, we immobilized the recombinant endo-1,4-β-xylanase of Malbranchea pulchella (MpXyn10) in various chemical supports and evaluated its potential to produce xylooligosaccharides (XOS) from hydrothermal liquor of eucalyptus wood chips. Values >90% of immobilization yields were achieved from amino-activated supports for 120 min. The highest recovery values were found on Purolite (142%) and MANAE-MpXyn10 (137%) derivatives, which maintained more than 90% residual activity for 24 h at 70 °C, while the free-MpXyn10 maintained only 11%. In addition, active MpXyn10 derivatives were stable in the range of pH 4.0−6.0 and the presence of the furfural and HMF compounds. MpXyn10 derivatives were tested to produce XOS from xylan of various sources. Maximum values were observed for birchwood xylan at 8.6 mg mL−1 and wheat arabinoxylan at 8.9 mg mL−1, using Purolite-MpXyn10. Its derivative was also successfully applied in the hydrolysis of soluble xylan present in hydrothermal liquor, with 0.9 mg mL−1 of XOS after 3 h at 50 °C. This derivative maintained more than 80% XOS yield after six cycles of the assay. The results obtained provide a basis for the application of immobilized MpXyn10 to produce XOS with high purity and other high-value-added products in the lignocellulosic biorefinery field.

Climate Change Impact on Yield and Water Use of Rice-Wheat Rotation System in the Huang-Huai-Hai Plain, China

Global climate change has had a significant impact on crop production and agricultural water use. Investigating different future climate scenarios and their possible impacts on crop production and water consumption is critical for proposing effective responses to climate change. In this study, based on daily downscaled climate data from 22 Global Climate Models (GCMs) provided by Coupled Model Intercomparison Project Phase 6 (CMIP6), we applied the well-validated Agricultural Production Systems sIMulator (APSIM) to simulate crop phenology, yield, and water use of the rice-wheat rotation at four representative stations (including Hefei and Shouxian stations in Anhui province and Kunshan and Xuzhou stations in Jiangsu province) across the Huang-Huai-Hai Plain, China during the 2041-2070 period (2050s) under four Shared Socioeconomic Pathways (i.e., SSP126, SSP245, SSP370, and SSP585). The results showed a significant increase in annual mean temperature (Temp) and solar radiation (Rad), and annual total precipitation (Prec) at four investigated stations, except Rad under SSP370. Climate change mainly leads to a consistent advance in wheat phenology, but inconsistent trends in rice phenology across four stations. Moreover, the reproductive growth period (RGP) of wheat was prolonged while that of rice was shorted at three of four stations. Both rice and wheat yields were negatively correlated with Temp, but positively correlated with Rad, Prec, and CO₂ concentration ([CO2]). However, crop ET was positively correlated with Rad, but negatively correlated with [CO2], as elevated [CO2] decreased stomatal conductance. Moreover, the water use efficiency (WUE) of rice and wheat was negatively correlated with Temp, but positively correlated with [CO2]. Overall, our study indicated that the change in Temp, Rad, Prec, and [CO2] have different impacts on different crops and at different stations. Therefore, in the impact assessment for climate change, it is necessary to explore and analyze different crops in different regions. Additionally, our study helps to improve understanding of the impacts of climate change on crop production and water consumption and provides data support for the sustainable development of agriculture.

Mechanical pretreatment of lignocellulosic biomass toward enzymatic/fermentative valorization

Lignocellulosic biomass (LCB) has the potential to replace fossil fuels, thanks to the concept of biorefinery. This material is formed mainly by cellulose, lignin, and hemicellulose. To maximize the valorization potential of this material, LCB needs to be pretreated. Milling is always performed before any other treatments. It does not produce chemical change and improves the efficiency of the upcoming processes.

Additionally, it makes LCB easier to handle and increases bulk density and transfer phenomena of the next pretreatment step. However, this treatment is energy consuming, so it needs to be optimized. Several mills can be used, and the equipment selection depends on the characteristics of the material, the final size required, and the operational regime: continuous or batch. Among them, ball, knife, and hammer mills are the most used at the laboratory scale, especially before enzymatic or fermentative treatments. The continuous operational regime (knife and hammer mill) allows us to work with high volumes of raw material and can continuously reduce particle size, unlike the batch operating regime (ball mill).

This review recollects the information about the application of these machines, the effect on particle size, and subsequent treatments. On the one hand, ball milling reduced particle size the most; on the other hand, hammer and knife milling consumed less energy. Furthermore, the latter reached a small final particle size (units of millimeters) suitable for valorization.