Biomass Degradation Research Articles

Electrochemical characterization of a family AA10 LPMO and the impact of residues shaping the copper site on reactivity

Research on enzymes for lignocellulose biomass degradation has progressively increased in recent years due to the interest in taking advantage of this natural resource. Among these enzymes are the lytic polysaccharide monooxygenases (LPMOs) that oxidatively depolymerize crystalline cellulose using a reactive oxygen species generated in a reduced mono‑copper active site. The copper site comprises of a highly conserved histidine-brace, providing three equatorial nitrogen ligands, whereas less conserved residues close to the copper contribute to shaping and confining the site. The catalytic copper site is exposed to the solvent and to the crystalline substrates, and as so, the influence of the copper environment on LPMO properties, including the redox potential, is of great interest. In the current work, a direct electrochemical study of an LPMO (ScLPMO10C) was conducted allowing to retrieve kinetic and thermodynamic data associated with the redox transition in the catalytic centre. Moreover, two residues that do not bind to the copper but shape the copper sites were mutated, and the properties of the mutants were compared with those of the wild-type enzyme. The direct electrochemical studies, using cyclic voltammetry, yielded redox potentials in the +200 mV range, well in line with LPMO redox potentials determined by other methods. Interestingly, while the mutations hardly affected the formal redox potential of the enzyme, they drastically affected the reactivity of the copper site and enzyme functionality.

Environmental degradation of cellulose under anaerobic conditions

Cellulose is a primary structural component of plants and is one of the most abundant polymers on the Earth. Degradation of this recalcitrant component of plant biomass is an important process in the global carbon cycle and can potentially provide feedstock for biofuels. Fungi and bacteria are the primary organisms able to breakdown biomass-derived cellulose. Anaerobic bacteria, present in cellulose degrading ecosystems, such as compost piles, soils rich in organic matter, aquatic sediments, and digestive systems of herbivores, have developed efficient pathways to maximize metabolic energy from biomass degradation. In the absence of terminal electron acceptors, such as oxygen, hydrogen-producing pathways are common methods of electron carrier recycling. Electron bifurcating systems linked to hydrogen metabolism play an important role in anaerobic metabolism. In this study, samples from environmental cellulose-degrading microbial communities were collected, and the metabolic products produced during anaerobic cellulose degradation were examined. Samples from different environments produced different fermentation products from cellulose, suggesting flexibility in the fermentative degradation pathways. The most abundant products observed included hydrogen, acetate, propionate, butyrate, ethanol, and methane.

Investigating lytic polysaccharide monooxygenase-assisted wood cell wall degradation with microsensors

Lytic polysaccharide monooxygenase (LPMO) supports biomass hydrolysis by increasing saccharification efficiency and rate. Recent studies demonstrate that H2O2 rather than O2 is the cosubstrate of the LPMO-catalyzed depolymerization of polysaccharides. Some studies have questioned the physiological relevance of the H2O2-based mechanism for plant cell wall degradation. This study reports the localized and time-resolved determination of LPMO activity on poplar wood cell walls by measuring the H2O2 concentration in their vicinity with a piezo-controlled H2O2 microsensor. The investigated Neurospora crassa LPMO binds to the inner cell wall layer and consumes enzymatically generated H2O2. The results point towards a high catalytic efficiency of LPMO at a low H2O2 concentration that auxiliary oxidoreductases in fungal secretomes can easily generate. Measurements with a glucose microbiosensor additionally demonstrate that LPMO promotes cellobiohydrolase activity on wood cell walls and plays a synergistic role in the fungal extracellular catabolism and in industrial biomass degradation.

High productivity promoted exceptional fossil preservation of the early Middle Triassic Luoping biota of Yunnan Province, China

The early Middle Triassic (Anisian) Luoping biota is representative of marine ecosystems following their full recovery after the Permian-Triassic mass extinction; however, its exceptional preservation remains poorly understood. In this paper, we report multiple geochemical proxies (TOC, TN, P/Al, Cuxs, Nixs, Baxs, δ13Ccarb, and δ13Corg) from Member II of the Middle Triassic Guanling Formation at the Xiangdongpo section in Luoping County, Yunnan Province, China, to assess the relationship between primary productivity and exceptional preservation of the Luoping biota. Variations in TOC, TN, P/Al, Cuxs, and Nixs values show that exceptional preservation coincides with two intervals of high productivity. Relatively low C/N ratios and distributed Δ13Ccarb-org values indicate that primary productivity was dominated by eukaryotic algae and prokaryotic microbes. Based on geochemical analyses and regional correlations, we conclude that, following sea level rise, nutrients were supplied to the Luoping area by upwelling from the open ocean and facilitated the blooming of marine communities in an open platform setting. In the intra-platform depression, increased nutrients supply also fueled high primary productivity in surface waters and oxygen consumption in the water column, causing bottom water anoxia. The lack of oxygen in the bottom water reduced the rate of biomass degradation and bioturbation, promoting growth of microbial mats, leading to the exceptional preservation of macrofauna. This study highlights the important role of elevated primary productivity in exceptional fossil preservation by triggering anoxia of bottom waters. Our findings confirm the widespread development of anoxic conditions during the middle Anisian (Pelsonian), from the eastern Tethys to the Panthalassa, and also reveal the interactions between organisms and the environment after Permian-Triassic mass extinction.

Design and synthesis of SO3H-functionalized acidic ionic liquids for catalytic conversion of wheat straw to ethyl levulinate

Ethyl levulinate (EL) is a key platform compound for the catalytic conversion of biomass. Ionic liquids (ILs) have attracted much attention due to their unique tunable structures and wide range of applications, a series of SO3H-functionalized imidazole based acidic ILs were designed and synthesized. These SO3H-functionalized ILs were used as the catalyst to be applied to the conversion of the wheat straw to EL. Among them, SimIL-6 exhibited good catalytic performance for the conversion of wheat straw to EL in ethanol. When the concentration of SimIL-6 was 30 mmol/L, the yield of EL could reach 20.1 wt% at 180 ℃ for 2 h. Furthermore, SimIL-6 as the catalyst was reused at least six times without significant reduction in catalytic efficiency. This work shed light on a new approach towards the full utilization of biomass and efficient degradation of biomass to EL.

A Review Study of Immobilized Microbial-Nanoparticles: Techniques and Biotechnology Applications

Immobilization of microbial cells on nanomaterials opens up broad prospects in biotechnology applications including environmental pollution control and enhancement of biofuel production. Cell-immobilization contributes to improved microbial performance, protection of microbes, and further biomass degradation. Moreover, nanoparticles as biomass support is an advanced strategy in bioremediation. Nanoparticles are interesting for immobilizing microbes due to their unique physicochemical properties. This review throws some light on the recent advances in immobilization of microbial cells techniques onto nanoparticles as a carrier where they are subsequently used as an nano-bio-stimulator in bioprocessing. The benefits and drawbacks of immobilization techniques are included. The biotechnology applications of nano-biocatalyst in bioprocessing are covered including biosorption of pollutants from wastewater and stimulants in biofuel production processes for a green energy generation. The use of nano-bio-catalysts in bioprocesses is an effective strategy for achieving economic feasibility in many processes. Furthermore, future prospects for microbial cell immobilization techniques are discussed.

Гидролиз компонентов растительной биомассы как универсальный механизм экобезопасности природных и синтетических материалов

Hydrolysis of protein-polysaccharide components of plant materials under basic environmental conditions is the main mechanism of biochemical degradation of biomass in nature. Most modern synthetic polymeric materials do not have the ability to rapidly degrade in the environment after the end of their useful life. The aim of the work was to compare the kinetics of hydrolysis of protein-polysaccharide substances of plant origin and artificially created synthetic polymeric materials with biomarker units. The article studies the kinetics of hydrolysis of the basic constituents of natural materials on the example of model systems — vegetable protein of soy origin and vegetable carbohydrate — starch in comparison with the possible enzymatic biodegradation of a synthetic copolymer used for surface treatment of wood products — a copolymer of glycerol and phthalic anhydride. A methodology for the possible modification of the synthesis of such copolymers by introducing lactic acid fluctuation units into their structure, which increase the bioactivity of the polymer material, is described. The effect of lactic acid units in the composition of synthetic tercopolymer on the rate of its biodegradation has been revealed. The main kinetic constants of the decay rates and activation energies of the enzymatic hydrolysis of the studied objects were determined under conditions simulating their possible biodegradation in the environment. The values of the constants of the maximum rates of pancreatic biodegradation Vmax.102, ranged from 0,24 mg/ml·min–1 for the synthesized tercopolymer of glycerol, phthalic anhydride and lactic acid compared with similar values at the level of 1,43...2,29 mg /ml·min–1 for protein-polysaccharide substrates. It is shown that substances of a protein nature have the highest rate of biodegradation, and a synthetic copolymer of glycerol and phthalic anhydride in the form of glyphthalic resin has a significant resistance to biodegradation. Modification of such a copolymer by introducing lactic acid units into its structure makes it possible to increase its biodegradability. The expediency of modifying the eco-properties of synthetic polymers by introducing lactic acid units into their structure, which increase the biodegradability, has been confirmed.

Effect of Microwave Pre-Treatment of Biomass on the Thermal Oxidative Conversion of Biomass Blends Containing Pre-Treated and Raw Biomass of Different Origination in Terms of Processing Rate and Heat Production

In this paper, the thermochemical conversion of selectively pre-treated binary blends composed of 30% microwave (MW) pre-treated biomass pellets (wheat straw, wood) and 70% of different origin raw biomass pellets (wheat straw, wood, or peat) was performed using originally developed experimental device with a heat output up to 20 kW. Biomass pellets were pre-treated at temperatures of 200 and 275 °C using a microwave laboratory scale torrefaction of the original construction. It was established that synergistic effects of interaction between the components of binary blends promote an increase in the efficiency of their thermochemical conversion by 5.8–9.4%. It was assumed that synergistic effects of thermochemical conversion can be related to an increase in surface area and porosity of pre-treated pellets. With a focus on different steps and rates of biomass degradation and heat amounts released for different types of blends, the thermal analysis (DTG/DSC) of ground blends in the temperature range of 25–650 °C was performed in air media with the heating rate of 10 °C/min. According to the thermal analysis data, the heat energy yield of ground blends meets the requirements of linear regression based on the additivity principle and the development of synergistic effects during thermochemical conversion of ground blends was not detected.

A Horseradish Peroxidase-Mediator System for Benzylic C-H Activation.

Enzyme-mediator systems generate radical intermediates that abstract hydrogen atoms under mild conditions. These systems have been employed extensively for alcohol oxidation, primarily in biomass degradation, but they are underexplored for direct activation of C(sp3)-H bonds in alkyl groups. Here, we combine horseradish peroxidase (HRP), H2O2, and redox mediator N-hydroxyphthalimide (NHPI) for C(sp3)-H functionalization of alkylbenzene-type substrates. The HRP-NHPI system is >10-fold more active than existing enzyme-mediator systems in converting alkylbenzenes to ketones and aldehydes under air, and it operates from 0-50 °C and in numerous aqueous-organic solvent mixtures. The benzylic substrate radical can be trapped through a reaction with NHPI, demonstrating the formation of benzylic products beyond ketones. Furthermore, we demonstrate a one-pot, two-step enzymatic cascade for converting alkylbenzenes to benzylic amines. Overall, the HRP-NHPI system enables the selective benzylic C-H functionalization of diverse substrates under mild conditions using a straightforward procedure.

Waste Biomass Selective and Sustainable Photooxidation to High-Added-Value Products: A Review

Researchers worldwide seek to develop convenient, green, and ecological production processes to synthesize chemical products with high added value. In this sense, lignocellulosic biomass photocatalysis is an excellent process for obtaining various outcomes for the industry. One issue of biomass transformation via heterogeneous catalysis into valuable chemicals is the selection of an adequate catalyst that ensures high conversion and selectivity at low costs. Titanium oxide (TiO2), is widely used for several applications, including photocatalytic biomass degradation, depolymerization, and transformation. Graphite carbon nitride (g-C3N4) is a metal-free polymeric semiconductor with high oxidation and temperature resistance and there is a recent interest in developing this catalyst. Both catalysts are amenable to industrial production, relatively easy to dope, and suited for solar light absorption. Recent investigations also show the advantages of using heterojunctions, for biomass derivates production, due to their better solar spectrum absorption properties and, thus, higher efficiency, conversion, and selectivity over a broader spectrum. This work summarizes recent studies that maximize selectivity and conversion of biomass using photocatalysts based on TiO2 and g-C3N4 as supports, as well as the advantages of using metals, heterojunctions, and macromolecules in converting cellulose and lignin. The results presented show that heterogeneous photocatalysis is an interesting technology for obtaining several chemicals of industrial use, especially when using TiO2 and g-C3N4 doped with metals, heterojunctions, and macromolecules because these modified catalysts permit higher conversion and selectivity, milder reaction conditions, and reduced cost due to solar light utilization. In order to apply these technologies, it is essential to adopt government policies that promote the use of photocatalysts in the industry, in addition to encouraging active collaboration between photooxidation research groups and companies that process lignocellulosic biomass.

Bioelectrochemical performance of microbial fuel cell powered electro-Fenton system (MFCⓅEFs) with composite PANI-Mn/CF anode

Microbial fuel cell powered electro-Fenton system (MFCⓅEFs) is a self-sustainable energy conversion process to degrade refractory pollutants utilizing green biomass energy. Most previous works usually employed innovative cathode to minimize electron transfer losses but neglected the development of high-efficiency anode to enhance electron generation. The synergy of polyaniline (PANI) and MnO<sub>2</sub> on electrode could improve charge accessibility and facilitate rapid electron transfer due to its superior conductivity and capacitance, which had not been applied to MFCⓅEFs as anode so far. In this study, a PANI-Mn/CF (carbon fiber loaded with polyaniline and MnO<sub>2</sub>) composite anode was introduced into MFCⓅEFs to enhance interface activity and realize more efficient electricity generation and pollutant degradation. Experimental results showed that a higher power density (5.49 times that of the original CF) and lower ohmic resistance (7.17 Ω) occurred in the MFCⓅEFs with PANI-Mn/CF anode, which consumed more sewage sludge (37.14% of TCOD removal), leading to achieving more effective pollutant degradation (93.03% of tetracycline hydrochloride removal). Overall, this study provided an innovative way of thinking and approach to efficient utilization of biomass waste and degradation of refractory pollutants with the merits of environmental sustainability.

Metagenomic Analysis of in Vitro Ruminal Fermentation Reveals the Role of the Copresent Microbiome in Plant Biomass Degradation.

In vitro ruminal fermentation is considered an efficient way to degrade crop residue. To better understand the microbial communities and their functions during in vitro ruminal fermentation, the microbiome and short chain fatty acid (SCFA) production were investigated using the metagenomic sequencing and rumen simulation technique (RUSITEC) system. A total of 1677 metagenome-assembled genomes (MAGs) were reconstructed, and 298 MAGs were found copresenting in metagenomic data of the current work and 58 previously ruminal representative samples. Additionally, the domains related to pectin and xylan degradation were overrepresented in the copresent MAGs compared with total MAGs. Among the copresent MAGs, we obtained 14 MAGs with SCFA-synthesis-related genes positively correlated with SCFA concentrations. The MAGs obtained from this study enable a better understanding of dominant microbial communities across in vivo and in vitro ruminal fermentation and show promise for pointing out directions for further research on in vitro ruminal fermentation.

In Vitro Antibacterial and Anti-Inflammatory Activity of Arctostaphylos uva-ursi Leaf Extract against Cutibacterium acnes.

Cutibacterium acnes (C. acnes) is the main causative agent of acne vulgaris. The study aims to evaluate the antimicrobial activity of a natural product, Arctostaphylos uva-ursi leaf extract, against C. acnes. Preliminary chemical–physical characterization of the extract was carried out by means of FT-IR, TGA and XPS analyses. Skin permeation kinetics of the extract conveyed by a toning lotion was studied in vitro by Franz diffusion cell, monitoring the permeated arbutin (as the target component of the extract) and the total phenols by HPLC and UV-visible spectrophotometry, respectively. Antimicrobial activity and time-killing assays were performed to evaluate the effects of Arctostaphylos uva-ursi leaf extract against planktonic C. acnes. The influence of different Arctostaphylos uva-ursi leaf extract concentrations on the biofilm biomass inhibition and degradation was evaluated by the crystal violet (CV) method. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) test was used to determine the viability of immortalized human keratinocytes (HaCaT) after exposure to Arctostaphylos uva-ursi leaf extract for 24 and 48 h. Levels of interleukin (IL)-1β, IL-6, IL-8 and tumour necrosis factor (TNF)-α were quantified after HaCaT cells cotreatment with Arctostaphylos uva-ursi leaf extract and heat-killed C. acnes. The minimum inhibitory concentration (MIC) which exerted a bacteriostatic action on 90% of planktonic C. acnes (MIC90) was 0.6 mg/mL. Furthermore, MIC and sub-MIC concentrations influenced the biofilm formation phases, recording a percentage of inhibition that exceeded 50 and 40% at 0.6 and 0.3 mg/mL. Arctostaphylos uva-ursi leaf extract disrupted biofilm biomass of 57 and 45% at the same concentrations mentioned above. Active Arctostaphylos uva-ursi leaf extract doses did not affect the viability of HaCaT cells. On the other hand, at 1.25 and 0.6 mg/mL, complete inhibition of the secretion of pro-inflammatory cytokines was recorded. Taken together, these results indicate that Arctostaphylos uva-ursi leaf extract could represent a natural product to counter the virulence of C. acnes, representing a new alternative therapeutic option for the treatment of acne vulgaris.

Microbial community dynamics during the storage of industrial-scale wood chip piles of Picea abies and Populus canadensis and the impact of an alkaline stabilization agent

Storage of woody biomass in large wood chip piles is unavoidable for biotechnological applications, but comes along with considerable biomass-, energy- and thus, economic losses due to exothermic reactions and microbial degradation. The homogeneous amendment of the storage piles with an alkaline stabilization agent, calcium hydroxide (Ca(OH)2), was found to decrease dry matter loss in Picea abies; for Populus canadensis piles the effects cannot clearly be deduced. Here we investigated the bacterial and fungal communities of industrial-scale wood chip piles (250 m3) of these two different tree species and related them to physicochemical conditions and enzymatic activities after 35 and 120 d, representing short- and long-term storage of the wood chips, respectively. Coming from different wood types (hard vs. softwood), we expected the communities to converge over time, due to similar storage conditions. Despite pH posing selective pressure, we expected a minor Ca(OH)2 effect as already known from previous studies.We found that the effectiveness of Ca(OH)2 addition depended on the wood type that determined both the native microbial seeding community and temperature pattern of all piles, thereby exerting selective forces of differing strength. Generally, a thermophilic community consisting of single fungal and variable bacterial taxa were identified. As expected, the microbial communities from P. abies and P. canadensis converged over time. Biomass loss was connected to C-cycle related enzymatic activities and to the abundance and composition of fungal communities. Chaetomium sp. was identified as potential key taxon determining biomass degradation under the given storage conditions.

Aspergillus spp., a versatile cell factory for enzymes and metabolites: Interventions through genome editing

Aspergillus sp. is widely distributed in nature and plays significant roles in the degradation of lignocellulose biomass and extensively used in bioprocess and fermentation technology and many species are also a generally regarded safe. Many of the Aspergillus species are established cell factories due to their inherent capacity in secreting large number of hydrolytic enzymes. With the advent of next generation genomic technologies and metabolic engineering technologies, the production potential of Aspergillus cell factory has improved over the years. Various genome editing tools has been developed for Aspergillus like engineered nucleases, zinc finger nucleases, TALEN and CRISPR-Cas9 system. Currently, the CRISPR/Cas9-based technique is extensively used to enhance the effectiveness of gene manipulation in model system Aspergillus nidulans and other strains like Aspergillus oryzae, Aspergillus niger and Aspergillus fumigatus. This review describes the recent developments of genome editing technologies in Aspergillus the synthesis of heterologous proteins and secondary metabolites in the Aspergillus species.

Prospects of soil microbiome application for lignocellulosic biomass degradation: An overview.

Sustainable and practically viable biofuels production technology using lignocellulosic biomass is still seeking its way of implementation owing to some major issues involved therein. Unavailability of efficient microbial sources for the degradation of cellulosic biomass is one of the major roadblocks in biomass to biofuels production technology. In this context, utilization of microbiomes to degrade lignocellulaosic biomass is emerging as a rapid and effective approach that can fulfill the requirements of biomass based biofuels production technology. Therefore, the present review is targeted to explore soil metagenomic approach to improve the lignocellulosic biomass degradation processing for the cost-effective and eco-friendly application. Soil microbiomes consist of rich microbial community along with high probability of cellulolytic microbes, and can be identified by culture independent metagenomics method which can be structurally and functionally explored via genomic library. Therefore, in depth analysis and discussion have also been made via structural & functional metagenomics tools along with their contribution to genomic library. Additionally, the present review highlights currently existing bottlenecks along with their feasible solutions. This review will help to understand the basic research as well as industrial concept for the process improvement based on soil microbiome mediated lignocellulosic biomass degradation, and this may likely to implement for the low-cost commercial biofuels production technology.

Research Progress on Lignocellulosic Biomass Degradation Catalyzed by Enzymatic Nanomaterials

Lignocellulose biomass (LCB) has extensive applications in many fields such as bioenergy, food, medicines, and raw materials for producing value-added products. One of the keys to efficient utilization of LCB is to obtain directly available oligo- and monomers (e. g., glucose). With the characteristics of easy recovery and separation, high efficiency, economy, and environmental protection, immobilized enzymes have been developed as heterogeneous catalysts to degrade LCB effectively. In this review, applications and mechanisms of LCB-degrading enzymes are discussed, and the nanomaterials and methods used to immobilize enzymes are also discussed. Finally, the research progress of lignocellulose biodegradation catalyzed by nano-enzymes was discussed.

A chemoproteomic approach to identify redox-active methionines in secreted proteins of saprophytic fungi during biomass degradation

A chemoproteomic approach to identify redox-active methionines in secreted proteins of saprophytic fungi during biomass degradation

Lignocellulosic biomass based microbial fuel cells: Performance and applications

Lignocellulosic biomass has the potential to replace fossil fuels as a sustainable and renewable feedstock for energy generation . Microbial fuel cell technology offers an energy-producing system from lignocellulosic biomass. This review explores different microbial fuel cell designs i.e. membrane-less single chambered, double chambered and integrated microbial fuel cell along with their mode of operation. There are some compatibility issues with different microbial fuel cell designs in utilizing the lignocellulosic biomass as feed. Microbial fuel cell setup with integrated pre-treatment or simultaneous degradation of lignocellulosic biomass may provide a solution. A careful selection of microbial community according to the microbial fuel cell operation conditions along with upscaling of the system may help in efficient utilization of renewable energy sources . Thus, lignocellulosic biomass-based microbial fuel cell may potentially be used in the bioremediation, production of biofuels and industrially important value-added products along with simultaneous production of electricity. • Lignocellulosic biomass may be used as a renewable feedstock in microbial fuel cells. • Microbial fuel cell designs influence the substrate utilization efficiency. • Pre-treatment of lignocellulosic biomass is required to be used as feed. • Such eco-friendly technology may be used for several applications.

Impacts of Anaerobic Co-Digestion on Different Influencing Parameters: A Critical Review

Lignocellulosic feedstocks are year-round, available bio-residues that are the right candidates for counteracting the energy crises and global warming facing the world today. However, lignin leads to a slow hydrolysis rate and is a major bottleneck for biogas production via anaerobic digestion. Anaerobic co-digestion (AcoD) is an economical method available, which overcomes the limitation of a single feedstock’s properties in an anaerobic digestion process. This paper critically reviews the impacts of co-digestion on lignocellulosic biomass degradation, process stability, various working parameters, and microbial activities that improve methane yields. A combination of compatible substrates is chosen to improve the biomethane yield and conversion rate of organic matter. AcoD is a promising method in the delignification of lignocellulosic biomass as an acid pretreatment. Ultimate practices to control the impact of co-digestion on system performances include co-feed selection, in terms of both carbon-to-nitrogen (C/N) and mixing ratios, and other operating conditions. A detailed analysis is performed using data reported in the recent past to assess the sensitivity of influencing parameters on the resultant biogas yield. For the investigators motivated by the basic principles of AcoD technology, this review paper generates baseline data for further research work around co-digestion.