Inhibition of lignin-derived phenolic compounds to cellulase

Biodetoxification of Lignocellulose Hydrolysate for Direct Use in Succinic Acid Production

The pretreatment of lignocellulosic biomass with acid generates phenolic and furanyl compounds that function as toxins by inhibiting microbial growth and metabolism. Therefore, it is necessary to detoxify acid-pretreated lignocellulosic biomass for better utilization. Among the various detoxification methods that are available, biodetoxification offers advantages that include mild reaction conditions and low energy consumption. In this study, a newly isolated Rhodococcus aetherivorans strain, N1, was found to effectively degrade various lignin-derived aromatic compounds, such as p-coumarate, ferulate, syringaldehyde, furfural, and 5-hydroxymethylfurfural. Furthermore, the metabolic pathway and genes responsible for this degradation were also identified. In addition, the overexpression of a demethylase (DesA) and 3,4-dioxygenase (DesZ) in strain N1 generated a recombinant strain, N1-S, which showed an enhanced ability to degrade syringaldehyde and 80.5% furfural, 50.7% 5-hydroxymethylfurfural, and 71.5% phenolic compounds in corn cob hydrolysate. The resulting detoxified hydrolysate was used directly as a feedstock for succinate production by Escherichia coli suc260. This afforded 35.3 g/l succinate, which was 6.5 times greater than the concentration afforded when nondetoxified hydrolysate was used. Overall, the results of this study demonstrate that strain N1-S is a valuable microbe for the biodetoxification of lignocellulosic biomass.

Toxicants improve glycerol production in the fermentation of undetoxified hydrolysate by Candida glycerinogenes

OBJECTIVES

Toxicants inhibit microbial fermentation and reduce product titres. This work investigated the glycerol production characteristics of Candida glycerinogenes in highly toxic unwashed undetoxified hydrolysate and provided new ideas for high glycerol production from hydrolysates.

RESULTS

The unwashed hydrolysate contains higher concentrations of toxicants, such as furfural, acetic acid, phenols and NaCl than the washed alkali-treated bagasse hydrolysate. C. glycerinogenes fermented unwashed undetoxified hydrolysate yielded 36.1 g/L glycerol, 15.8% higher than the washed hydrolysate, suggesting that the toxicants stimulated glycerol synthesis. qRT-PCR analysis showed that toxicants of unwashed undetoxified hydrolysates greatly up-regulated the transcript levels of the genes GPD1, HXT4 and MSN4 et al. Overexpressing the above genes increased glycerol production by 27.9% to 46.1 g/L. And it was further increased by 8.8% to 50.1 g/L in a 5 L bioreactor.

CONCLUSIONS

This result proves that toxicants in lignocellulosic hydrolysates can increase the titre of microbial glycerol production.

Effects of hematite on two types of dissolved organic compounds in lignocellulosic anaerobic hydrolysate: Lignin-derived aromatic compounds and denitrifying carbon sources

The utilization of anaerobic hydrolysate from agroforestry wastes is limited by dissolved lignin and aromatics, which have received insufficient attention despite their potential as excellent carbon sources for denitrification. This study aims to investigate the influence of hematite on lignin-derived aromatic compounds and denitrifying carbon sources, as well as to identify iron-reducing bacteria that utilize lignin-derived aromatic compounds as electron donors. The findings revealed that hematite facilitated the anaerobic fermentation of plant biomass, resulting in the production of small molecular organic acids. Moreover, biodegradation of lignin-derived aromatic compounds led to the formation of phenolic acids, while an increased generation of denitrifying carbon sources enhanced nitrogen removal efficiency by 13.84 %. Additionally, due to adsorption by hematite and subsequent microbial degradation, there was a significant improvement (40.32%) in color removal rate within denitrification effluent. Notably, Azonexus strains were hypothesized to be involved in Fe(Ⅲ) reduction coupled with aromatic compounds oxidation.

Molecular insights into inhibiting effects of lignin on cellulase investigated by molecular dynamics simulation

The hydrolysis of lignocellulose into fermentable monosaccharides using cellulases represents a critical stage in lignocellulosic bioconversion. However, the inactivation of cellulase in the presence of lignin is attributed to the high cost of biofinery. To address this challenge, a comprehensive investigation into the structure-function relationship underlying lignin-driven cellulase inactivation is essential. In this study, molecular docking and molecular dynamics (MD) simulations were employed to explore the impacts of lignin fragments on the catalytic efficiency of cellulase at the atomic level. The findings revealed that soluble lignin fragments and cellulose could spontaneously form stable complexes with cellulase, indicating a competitive binding scenario. The enzyme's structure remained unchanged upon binding to lignin. Furthermore, specific amino acid residues have been identified as involved in interactions with lignin and cellulose. Hydrophobic interactions were found to dominate the binding of lignin to cellulase. Based on the mechanisms underlying the interactions between lignin fragments and cellulase, decreased hydrophobicity and change in the charge of lignin may mitigate the inhibition of cellulase. Furthermore, site mutations and chemical modification are also feasible to improve the efficiency of cellulase. This study may contribute valuable insights into the design of more lignin-resistant enzymes and the optimization of lignocellulosic pretreatment technologies.Communicated by Ramaswamy H. Sarma.

Enhanced enzymatic sugar production from corn stover by combination of water extraction and glycerol-assisted instant catapult steam explosion

Glycerol-assisted instant catapult steam explosion (ICSE) of lignocellulose is an effective pretreatment method for enhancing sugar production compared to glycerol-free ICSE. In this study, glycerol-assisted ICSE of corn stover was studied in order to understand the reaction mechanisms and further optimize the process. Results showed that water extraction of corn stover prior to ICSE reduced pseudo-lignin formation. The combination of water extraction and glycerol-assisted ICSE led to the formation of lignin with a lower molecular weight (Mw) of 2851 g/mol than 3521 g/mole of that from the combination of water extraction and glycerol-free ICSE. 1H-13C NMR analysis revealed that glycerol likely reacted with lignin carboxylic OHs through esterification while etherification of aliphatic OHs was not observed in ICSE. These lignin analyses indicated that glycerol protected lignin from condensation/repolymerization during glycerol-assisted ICSE. Enzymatic hydrolysis results showed that without water extraction increasing glycerol usage from 0.2 kg/kg stover to 0.4 kg/kg stover improved glucan digestibility to 78% but further increase to 0.5 kg/kg stover reduced glucan digestibility. In addition, at the glycerol usage of 0.2-0.4 kg/kg stover, washing of pretreated stover for removal of glycerol and other biomass-derived compounds did not improve glucan digestibility compared to unwashed ones. Combination of water extraction and glycerol-assisted ICSE led to a high glucan digestibility of 89.7% and a total glucose yield of 25.5 g glucose/100 g stover, which were 30.1% and 7.5 g/100 g stover higher than those derived from glycerol-free ICSE of stover, respectively. Since glycerol is a low-cost carbon source, the resulting enzymatic hydrolysate that contained both glucose and glycerol may be directly used to produce bioproducts by microbial fermentation.

Systematic bioprospection for cellulolytic actinomycetes in the Chihuahuan Desert: isolation and enzymatic profiling

The quest for microbial cellulases has intensified as a response to global challenges in biofuel production. The efficient deconstruction of lignocellulosic biomass holds promise for generating valuable products in various industries such as food, textile, and detergents. This article presents a systematic bioprospection aimed at isolating actinomycetes with exceptional cellulose deconstruction capabilities. Our methodology explored the biodiverse oligotrophic region of Cuatro Cienegas, Coahuila, within the Chihuahuan Desert. Among the evaluated actinomycetes collection, 78% exhibited cellulolytic activity. Through a meticulous screening process based on enzymatic index evaluation, we identified a highly cellulolytic Streptomyces strain for further investigation. Submerged fermentation of this strain revealed an endoglucanase enzymatic activity of 149 U/mg. Genomic analysis of strain Streptomyces sp. STCH565-A revealed unique configurations of carbohydrate-active enzyme (CAZyme) genes, underscoring its potential for lignocellulosic bioconversion applications. These findings not only highlight the significance of the Chihuahuan Desert as a rich source of cellulolytic microorganisms but also offer insights into the systematic exploration and selection of high-performing cellulolytic microorganisms for application in diverse environmental contexts. In conclusion, our bioprospecting study lays a foundation for harnessing the cellulolytic potential of actinomycetes from the Chihuahuan Desert, with implications for advancing cellulose deconstruction processes in various industries. The findings can serve as a blueprint for future bioprospecting efforts in different regions, facilitating the targeted discovery of microorganisms with exceptional cellulosic deconstruction capabilities.

A combined liquid chromatography - trapped ion mobility - tandem high-resolution mass spectrometry and multivariate analysis approach for the determination of enzymatic reactivity descriptors in biomass hydrolysates

Intermediate products such as oxygenated compounds may interfere with bioconversion kinetics of lignocellulosic biomass into bioethanol. This work presents a multidimensional approach, based on liquid chromatography (LC), trapped ion mobility spectrometry (TIMS), tandem high-resolution mass spectrometry (HRMS/MS), and multivariate analysis, for the identification of enzymatic reactivity descriptors in 22 industrial biomass samples, called hydrolysates. The first part of the study is dedicated to the improvement of the chemical diversity assessment of the hydrolysates through an original three-dimensional Van Krevelen diagram displaying the double bond equivalent (DBE) as third dimension. In a second part, the evaluation of data by multivariate data analysis allowed the discrimination of sample according to the biomass type and the level of enzymatic reactivity. In the last part, a potential descriptor of low enzymatic reactivity was selected and used in a case study. An in-depth structural analysis was performed on the feature annotated as carbohydrate derivative. Considering the intricate fragmentation spectrum exhibited by the selected feature, trapped ion mobility was employed to enhance separation prior to the HRMS/MS experiments. This final step improved data interpretation and increased the identification confidence level leading to the characterization of xylotriose, 3,5-dimethoxy-4-hydroxybenzaldehyde and 4-hydroxy-3-methoxy-cinnamaldehyde. This is the first study to present an untargeted multidimensional approach for the identification of enzymatic hydrolysis inhibitors in industrial hydrolysate samples.

Mechanism of enhanced enzymatic hydrolysis performance by ethanol assisted deep eutectic solvent pretreatment- from the perspective of lignin

Valorization of lignocellulose has received a lot of attention due to the abundance of lignocellulosics. It was showed that synergistic carbohydrate conversion and delignification could be achieved via ethanol assisted DES (choline chloride/lactic acid) pretreatment. To explore the reaction mechanism of lignin in the DES, milled wood lignin obtained from Broussonetia papyrifera was subjected to pretreatment at critical temperatures. The results suggested that ethanol assistance could contribute the incorporation of ethyl groups and reduce condensation structures of Hibbert's ketone. Adding ethanol at 150 °C not only decreased formation of condensed G unit (from 7.23% to 0.87%), but also removed J and S' substructures, thus effectively reducing the adsorption of lignin on cellulase, and promoting the glucose yield after enzymatic hydrolysis.

Inhibition of enzyme hydrolysis of cellulose by phenols from hydrothermally pretreated sugarcane straw

Relatively few studies have addressed the characterization of sugarcane straw (SCS) for production of fermentable sugars through enzyme hydrolysis. Straw is a major co-product of the sugarcane harvest in Brazil that has potential to sustainably increase cellulosic feedstocks in Brazil by 50%. Pretreatment of 10% w/v straw with liquid hot water (LHW) at 180 °C for 50 min (severity, S_o, of 4.05), solubilizes hemicellulose, preserves glucan, and generates 4.49 g/L soluble phenolic compounds in the resulting liquid. Extracts from washing pretreated solids with excess hot water followed by acetone resulted in 1.10 and 0.83 g/L phenolics, respectively. Acetone-derived extracts were more inhibitory and decreased glucose yield for enzyme hydrolysis of Solka Floc (a lignin-free cellulose) by 42%. In comparison, pretreated straw washed with hot water or acetone was readily hydrolyzed to 92% and 97% by cellulase enzyme. Hydrothermally treated SCS has the potential to provide a valuable and added source of fermentable sugars suitable for bioprocessing into biofuels and bioproducts when cellulase enzyme inhibitors are removed after pretreatment.

Journey of lignin from a roadblock to bridge for lignocellulose biorefineries: A comprehensive review

The grave concerns arisen as a result of environmental pollution and diminishing fossil fuel reserves in the 21st century have shifted the focus on the use of sustainable and environment friendly alternative resources. Lignocellulosic biomass constituted by cellulose, hemicellulose and lignin is an abundantly available natural bioresource. Lignin, a natural biopolymer has over the years gained much importance as a high value material with commercial importance. The present review provides an in-depth knowledge on the journey of lignin from being considered a roadblock to a bridge connecting diverse industries with widescale applications. The successful valorization of lignin for the production of bio-based platform chemicals and fuels has been the subject of intensive investigation. A deeper understanding of lignin characteristics and factors governing the biomass conversion into valuable products can support improved biomass consumption. The components of lignocellulosic biomass might be totally transformed into a variety of value-added products with the improvements in bioprocess techniques that valorize lignin. In this review, the recent advances in the lignin extraction and depolymerization methods that may help in achieving the cost-economics of the bioprocess are summarized and compared. The industrial potential of lignin-derived products such as aromatics, biopolymers, biofuels and agrochemicals are also outlined. Additionally, assessment of the recent research trends in lignin valorization into value-added chemicals has been done and present scenario of technological-industrial applications of lignin with economic perspectives is highlighted.

Advances and perspectives on mass transfer and enzymatic hydrolysis in the enzyme-mediated lignocellulosic biorefinery: A review

Enzymatic hydrolysis is a critical process for the cellulase-mediated lignocellulosic biorefinery to produce sugar syrups that can be converted into a whole range of biofuels and biochemicals. Such a process operating at high-solid loadings (i.e., scarcely any free water or roughly ≥ 15% solids, w/w) is considered more economically feasible, as it can generate a high sugar concentration at low operation and capital costs. However, this approach remains restricted and incurs "high-solid effects", ultimately causing the lower hydrolysis yields with increasing solid loadings. The lack of available water leads to a highly viscous system with impaired mixing that exhibits strong transfer resistance and reaction limitation imposed on enzyme action. Evidently, high-solid enzymatic hydrolysis involves multi-scale mass transfer and multi-phase enzyme reaction, and thus requires a synergistic perspective of transfer and biotransformation to assess the interactions among water, biomass components, and cellulase enzymes. Porous particle characteristics of biomass and its interface properties determine the water form and distribution state surrounding the particles, which are summarized in this review aiming to identify the water-driven multi-scale/multi-phase bioprocesses. Further aided by the cognition of rheological behavior of biomass slurry, solute transfer theories, and enzyme kinetics, the coupling effects of flow-transfer-reaction are revealed under high-solid conditions. Based on the above basic features, this review lucidly explains the causes of high-solid hydrolysis hindrances, highlights the mismatched issues between transfer and reaction, and more importantly, presents the advanced strategies for transfer and reaction enhancements from the viewpoint of process optimization, reactor design, as well as enzyme/auxiliary additive customization.

A Chemical-Free Pretreatment for Biosynthesis of Bioethanol and Lipids from Lignocellulosic Biomass: An Industrially Relevant 2G Biorefinery Approach

A wide range of inorganic and organic chemicals are used during the pretreatment and enzymatic hydrolysis of lignocellulosic biomass to produce biofuels. Developing an industrially relevant 2G biorefinery process using such chemicals is challenging and requires more unit operations for downstream processing. A sustainable process has been developed to achieve industrially relevant titers of bioethanol with significant ethanol yield. The pretreatment of sorghum biomass was performed by a continuous pilot-scale hydrothermal reactor followed by disk milling. Enzymatic hydrolysis was performed without washing the pretreated biomass. Moreover, citrate buffer strength was reduced to 100-fold (50 mM to 0.5 mM) during the enzymatic hydrolysis. Enzymatic hydrolysis at 0.5 mM citrate buffer strength showed that significant sugar concentrations of 222 ± 2.3 to 241 ± 2.3 g/L (glucose + xylose) were attained at higher solids loadings of 50 to 60% (w/v). Furthermore, hydrolysates were fermented to produce bioethanol using two different xylose-fermenting Saccharomyces cerevisiae strains and a co-culture of xylose-fermenting and non-GMO yeast cultures. Bioethanol titer of 81.7 g/L was achieved with an ethanol yield of 0.48 gp/gs. Additionally, lipids were produced using the oleaginous yeast Rhodosporidium toruloides, yielding 13.2 g/L lipids with cellular lipid accumulation of 38.5% w/w from 100 g/L of sugar concentration. In summary, reducing the strength of the citrate buffer during enzymatic hydrolysis and omitting inorganic chemicals from the pretreatment process enhances the fermentability of hydrolysates and can also reduce operating costs.

Penicillium polonicum a new isolate obtained from Cerrado soil as a source of carbohydrate-active enzymes produced in response to sugarcane bagasse

Penicillium species have been studied as producers of plant cell wall degrading enzymes to deconstruct agricultural residues and to be applied in industrial processes. Natural environments containing decaying plant matter are ideal places for isolating fungal strains with cellulolytic and xylanolytic activities. In the present study, Cerrado soil samples were used as source of filamentous fungi able to degrade xylan and cellulose. Penicillium was the most abundant genus among the obtained xylan and carboxymethylcellulose degraders. Penicillium polonicum was one of the best enzyme producers in agar-plate assays. In addition, it secretes CMCase, Avicelase, pectinase, mannanase, and xylanase during growth in liquid media containing sugarcane bagasse as carbon source. The highest value for endo-β-1,4-xylanase activity was obtained after 4 days of growth. Xyl PP, a 20 kDa endo-β-1,4-xylanase, was purified and partially characterized. The purified enzyme presented the remarkable feature of being resistant to the lignin-derived phenolic compounds, p-coumaric and trans-ferulic acids. This feature calls for its further use in bioprocesses that use lignocellulose as feedstock. Furthermore, future work should explore its structural features which may contribute to the understanding of the relationship between its structure and resistance to phenolic compounds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03405-x.

Inhibition of cellulase activity by liquid hydrolysates from hydrothermally pretreated soybean straw

The one-pot biomass conversion process is a promising strategy to minimize potential product loss and reduce processing costs. However, this strategy has technical limitations due to the inhibitory effects of biomass components like lignin as well as the generated inhibitors (e.g., furans, phenols) during biomass processing. In this study, the inhibitory effects of liquid hydrolysates formed by hydrothermal pretreatment of soybean straw with either sodium hydroxide (NaOH) or hydrogen peroxide (H2O2) on cellulolytic enzyme activity were investigated. Hydrothermal pretreatment of soybean straw (10% w/v) was carried out with either sodium hydroxide (1% v/v) or hydrogen peroxide (1% v/v) at 121°C for 60 min to evaluate the effect of water-soluble inhibitors released from soybean pretreatment on cellulolytic enzyme activity. The fraction of cellulose in pretreated solids (1% w/v glucan) was enzymatically hydrolyzed for 72 h with 45 IU/g glucan (corresponding to 25 mg enzyme protein/g glucan) in the presence of either buffer or liquid hydrolysate generated from the pretreatments. Hydrolysis of NaOH and H2O2 pretreated solids resulted in 57% and 39% of glucose yields in buffer, respectively. In the presence of the liquid hydrolysates, NaOH and H2O2 pretreated biomass showed 20% and 30% glucose yield, respectively, indicating the enzyme suppression by inhibitors in the liquid hydrolysates. Of the enzyme activities in hydrolysates tested, NaOH hydrolysate showed a higher inhibitory effect on enzyme activities (mainly β-glucosidase) compared to H2O2 liquid, where enzyme deactivation has a first-order correlation and the manner in which the vacuum-filtered inhibitors were generated from pretreated soybean straw.

Towards efficient enzymatic saccharification of pretreated lignocellulose: Enzyme inhibition by lignin-derived phenolics and recent trends in mitigation strategies

Lignocellulosic biorefinery based on its sugar-platform has been considered as an efficient strategy to replace fossil fuel-based refinery. In the bioconversion process, pretreatment is an essential step to firstly open up lignocellulose cell wall structure and enhance the accessibility of carbohydrates to hydrolytic enzymes. However, various lignin and/or carbohydrates degradation products (e.g. phenolics, 5-hydroxymethylfurfural, furfural) also generated during pretreatment, which severely inhibit the following enzymatic hydrolysis and the downstream fermentation process. Among them, the lignin derived phenolics have been considered as the most inhibitory compounds and their inhibitory effects are highly dependent on the source of biomass and the type of pretreatment strategy. Although liquid-solid separation and subsequent washing can remove the lignin derived phenolics and other inhibitors, this is undesirable in the realistic industrial application where the whole slurry of pretreated biomass need to be directly used in the hydrolysis process. This review summarizes the phenolics formation mechanism for various commonly applied pretreatment methods and discusses the key factors that affect the inhibitory effect of phenolics on cellulose hydrolysis. In addition, the recent achievements on the rational design of inhibition mitigation strategies to boost cellulose hydrolysis for sugar-platform biorefinery are also introduced. This review also provides guidance for rational design detoxification strategies to facilitate whole slurry hydrolysis which helps to realize the industrialization of lignocellulose biorefinery.

Recent Advances in PLA-Based Antibacterial Food Packaging and Its Applications

In order to reduce environmental pollution and resource waste, food packaging materials should not only have good biodegradable ability but also effective antibacterial properties. Poly(lactic acid) (PLA) is the most commonly used biopolymer for food packaging applications. PLA has good physical properties, mechanical properties, biodegradability, and cell compatibility but does not have inherent antibacterial properties. Therefore, antibacterial packaging materials based on PLA need to add antibacterial agents to the polymer matrix. Natural antibacterial agents are widely used in food packaging materials due to their low toxicity. The high volatility of natural antibacterial agents restricts their application in food packaging materials. Therefore, appropriate processing methods are particularly important. This review introduces PLA-based natural antibacterial food packaging, and the composition and application of natural antibacterial agents are discussed. The properties of natural antibacterial agents, the technology of binding with the matrix, and the effect of inhibiting various bacteria are summarized.

Bioprocess development of 2, 3-butanediol production using agro-industrial residues

The valorization of agricultural and industrial wastes for fuel and chemical production benefits environmental sustainability. 2, 3-Butanediol (2,3-BDO) is a value-added platform chemical covering many industrial applications. Since the global market is increasing drastically, production rates have to increase. In order to replace the current petroleum-based 2,3-BDO production, renewable feedstock's ability has been studied for the past few decades. This study aims to find an improved bioprocess for producing 2,3-BDO from agricultural and industrial residues, consequently resulting in a low CO₂ emission bioprocess. For this, screening of 13 different biomass samples for hydrolyzable sugars has been done. Alkali pretreatment has been performed with the processed biomass and enzyme hydrolysis performed using commercial cellulase. Among all biomass hydrolysate oat hull and spruce bark biomass could produce the maximum amount of total reducing sugars. Later oat hull and spruce bark biomass with maximum hydrolyzable sugars have been selected for submerged fermentation studies using Enterobacter cloacae SG1. After fermentation, 37.59 and 26.74 g/L of 2,3-BDO was obtained with oat hull and spruce bark biomass, respectively. The compositional analysis of each step of biomass processing has been performed and changes in each component have been evaluated. The compositional analysis has revealed that biomass composition has changed significantly after pretreatment and hydrolysis leading to a remarkable release of sugars which can be utilized by bacteria for 2,3-BDO production. The results have been found to be promising, showing the potential of waste biomass residues as a low-cost raw material for 2,3-BDO production and thus a new lead in an efficient waste management approach for less CO₂ emission.

Metaproteomics reveals enzymatic strategies deployed by anaerobic microbiomes to maintain lignocellulose deconstruction at high solids

Economically viable production of cellulosic biofuels requires operation at high solids loadings—on the order of 15 wt%. To this end we characterize Nature’s ability to deconstruct and utilize mid-season switchgrass at increasing solid loadings using an anaerobic methanogenic microbiome. This community exhibits undiminished fractional carbohydrate solubilization at loadings ranging from 30 g/L to 150 g/L. Metaproteomic interrogation reveals marked increases in the abundance of specific carbohydrate-active enzyme classes. Significant enrichment of auxiliary activity family 6 enzymes at higher solids suggests a role for Fenton chemistry. Stress-response proteins accompanying these reactions are similarly upregulated at higher solids, as are β-glucosidases, xylosidases, carbohydrate-debranching, and pectin-acting enzymes—all of which indicate that removal of deconstruction inhibitors is important for observed undiminished solubilization. Our work provides insights into the mechanisms by which natural microbiomes effectively deconstruct and utilize lignocellulose at high solids loadings, informing the future development of defined cultures for efficient bioconversion.

Biological activity of multicomponent bio-hydrogels loaded with tragacanth gum

Producing hydrogels capable of mimicking the biomechanics of soft tissue remains a challenge. We explore the potential of plant-based hydrogels as polysaccharide tragacanth gum and antioxidant lignin nanoparticles in bioactive multicomponent hydrogels for tissue engineering. These natural components are combined with TEMPO-oxidized cellulose nanofibrils, a material with known shear thinning behavior. Hydrogels presented tragacanth gum (TG) concentration-dependent rheological properties suitable for extrusion 3D printing. TG enhanced the swelling capacity up to 645 % and the degradation rate up to 1.3 %/day for hydrogels containing 75 % of TG. Young's moduli of the hydrogels varied from 5.0 to 11.6 kPa and were comparable to soft tissues like skin and muscle. In vitro cell viability assays revealed that the scaffolds were non-toxic and promoted proliferation of hepatocellular carcinoma HepG2 cells. Therefore, the plant-based hydrogels designed in this work have a significant potential for tissue engineering.

Press water from the mechanical drying of Douglas-fir wood chips has multiple beneficial effects on lignocellulolytic fungi

BACKGROUND

The mechanical drying of wood chips is an innovative method that improves the heating value of sawmill by-products in an energy-efficient continuous process. The liquid that comes out of the wood chips as press water (PW), however, contains a variety of undissolved as well as dissolved organic substances. The disposal of the PW as wastewater would generate additional costs due to its high organic load, offsetting the benefits in energy costs associated with the enhanced heating value of the wood chips. Our research explored if the organic load in PW could be utilized as a substrate by cellulolytic filamentous fungi. Hence, using the industrially relevant Ascomycete Trichoderma reesei RUT-C30 as well as several Basidiomycete wood-rotting fungi, we examined the potential of press water obtained from Douglas-fir wood chips to be used in the growth and enzyme production media.

RESULTS

The addition of PW supernatant to liquid cultures of T. reesei RUT-C30 resulted in a significant enhancement of the endoglucanase and endoxylanase activities with a substantially shortened lag-phase. A partial replacement of Ca2+, Mg2+, K+, as well as a complete replacement of Fe2+, Mn2+, Zn2+ by supplementing PW of the liquid media was achieved without negative effects on enzyme production. Concentrations of PW above 50% showed no adverse effects regarding the achievable endoglucanase activity but affected the endoxylanase activity to some extent. Exploring the enhancing potential of several individual PW components after chemical analysis revealed that the observed lag-phase reduction of T. reesei RUT-C30 was not caused by the dissolved sugars and ions, nor the wood particles in the PW sediment, suggesting that other, so far non-identified, compounds are responsible. However, also the growth rate of several basidiomycetes was significantly enhanced by the supplementation of raw PW to the agar medium. Moreover, their cultivation in liquid cultures reduced the turbidity of the PW substantially.

CONCLUSIONS

PW was identified as a suitable media supplement for lignocellulolytic fungi, including the cellulase and xylanase producer T. reesei RUT-C30 and several wood-degrading basidiomycetes. The possibility to replace several minerals, trace elements and an equal volume of fresh water in liquid media with PW and the ability of fungal mycelia to filter out the suspended solids is a promising way to combine biological wastewater treatment with value-adding biotechnological applications.

Understanding the toxicity of lignin-derived phenolics towards enzymatic saccharification of lignocellulose for rationally developing effective in-situ mitigation strategies to maximize sugar production from lignocellulosic biorefinery

The lignin-derived phenolics are highly inhibitory toward lignocellulose enzymatic hydrolysis, while the relationship between phenolic structure and inhibitory effect is still not fully understood. In this study, the compositions of phenolics from dilute acid pretreated wheat straw were analyzed and their impact on cellulose hydrolysis was studied. With increase of pretreatment severity, more toxic phenolics were produced from lignin degradation reactions, which were the major contributor to the increased inhibitory effect of pretreatment hydrolysate towards cellulases. Through analyzing the relationship of phenolic structure and their inhibitory effect, a useful model was developed to predict the phenolics-caused inhibition by combining the indexes of electrophilicity and hydrophobicity. Further, through understanding the interactions between phenolics and cellulases, a novel biocomponent alleviator was rationally designed to block the phenolics-cellulase interactions, the degree of improvement of enzymatic hydrolysis reached as high as 135.8%. This study provides directions for developing more effective pretreatment and detoxification methods.

Modification of bioethanol production in an innovative pneumatic digester with non-thermal cold plasma detoxification

An anaerobic pneu-mechanical digester (PD) was designed to ferment lignocellulosic compounds. So, wheat and rice straws were pretreated using an ultrasound-acid, and then thermal-acid hydrolysis was conducted. Hydrolysis optimization was performed using the response surface method and the optimal points for time, temperature, and acid concentration were 45 min, 148.4 °C, and 2.04 % v/v, respectively. Cold plasma was then used as detoxification to reduce the amount of inhibitory compounds and acids. This method was capable of reducing the amounts of acetic acid, formic acid and furfural by 73, 83 and 68 % in hydrolyzed biomass, respectively. The biomass was fermented in a PD for 20 days and compared with a conventional digester (CD). The obtained results showed that the PD could increase the efficiency of bioethanol by 37 % in the detoxified state and 22 % in the non-detoxified state after 20 days of fermentation compared to the CD. Moreover, H₂S, CO and O₂ were measured during fermentation process. In PD, the amount of H₂S and O₂ was lower than CD, but CO was significantly higher in the PD.

Response mechanisms of Saccharomyces cerevisiae to the stress factors present in lignocellulose hydrolysate and strategies for constructing robust strains

Bioconversion of lignocellulosic biomass to biofuels such as bioethanol and high value-added products has attracted great interest in recent decades due to the carbon neutral nature of biomass feedstock. However, there are still many key technical difficulties for the industrial application of biomass bioconversion processes. One of the challenges associated with the microorganism Saccharomyces cerevisiae that is usually used for bioethanol production refers to the inhibition of the yeast by various stress factors. These inhibitive effects seriously restrict the growth and fermentation performance of the strains, resulting in reduced bioethanol production efficiency. Therefore, improving the stress response ability of the strains is of great significance for industrial production of bioethanol. In this article, the response mechanisms of S. cerevisiae to various hydrolysate-derived stress factors including organic acids, furan aldehydes, and phenolic compounds have been reviewed. Organic acids mainly stimulate cells to induce intracellular acidification, furan aldehydes mainly break the intracellular redox balance, and phenolic compounds have a greater effect on membrane homeostasis. These damages lead to inadequate intracellular energy supply and dysregulation of transcription and translation processes, and then activate a series of stress responses. The regulation mechanisms of S. cerevisiae in response to these stress factors are discussed with regard to the cell wall/membrane, energy, amino acids, transcriptional and translational, and redox regulation. The reported key target genes and transcription factors that contribute to the improvement of the strain performance are summarized. Furthermore, the genetic engineering strategies of constructing multilevel defense and eliminating stress effects are discussed in order to provide technical strategies for robust strain construction. It is recommended that robust S. cerevisiae can be constructed with the intervention of metabolic regulation based on the specific stress responses. Rational design with multilevel gene control and intensification of key enzymes can provide good strategies for construction of robust strains.

Improvement of Enzymatic Saccharification and Ethanol Production from Rice Straw Using Recycled Ionic Liquid: The Effect of Anti-Solvent Mixture

One of the major concerns for utilizing ionic liquid on an industrial scale is the cost involved in the production. Despite its proven pretreatment efficiency, expenses involved in its usage hinder its utilization. A better way to tackle this limitation could be overcome by studying the recyclability of ionic liquid. The current study has applied the Box–Behnken design (BBD) to optimize the pretreatment condition of rice straw through the usage of 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) as an ionic liquid. The model predicted the operation condition with 5% solid loading at 128.4 °C for 71.83 min as an optimum pretreatment condition. Under the optimized pretreatment condition, the necessity of the best anti-solvent was evaluated among water, acetone methanol, and their combinations. The study revealed that pure methanol is the suitable choice of anti-solvent, enhancing the highest sugar yield. Recyclability of EMIM-Ac coupled with anti-solvent was conducted up to five recycles following the predicted pretreatment condition. Fermentation studies evaluated the efficacy of recycled EMIM-Ac for ethanol production with 89% more ethanol production than the untreated rice straw even after five recycles. This study demonstrates the potential of recycled ionic liquid in ethanol production, thereby reducing the production cost at the industrial level.

Quantifying the inhibitory impact of soluble phenolics on anaerobic carbon mineralization in a thawing permafrost peatland

The mechanisms controlling the extraordinarily slow carbon (C) mineralization rates characteristic of Sphagnum-rich peatlands (“bogs”) are not fully understood, despite decades of research on this topic. Soluble phenolic compounds have been invoked as potentially significant contributors to bog peat recalcitrance due to their affinity to slow microbial metabolism and cell growth. Despite this potentially significant role, the effects of soluble phenolic compounds on bog peat C mineralization remain unclear. We analyzed this effect by manipulating the concentration of free soluble phenolics in anaerobic bog and fen peat incubations using water-soluble polyvinylpyrrolidone (“PVP”), a compound that binds with and inactivates phenolics, preventing phenolic-enzyme interactions. CO₂ and CH₄ production rates (end-products of anaerobic C mineralization) generally correlated positively with PVP concentration following Michaelis-Menten (M.M.) saturation functions. Using M.M. parameters, we estimated that the extent to which phenolics inhibit anaerobic CO₂ production was significantly higher in the bog—62 ± 16%—than the fen—14 ± 4%. This difference was found to be more substantial with regards to methane production—wherein phenolic inhibition for the bog was estimated at 54 ± 19%, while the fen demonstrated no apparent inhibition. Consistent with this habitat difference, we observed significantly higher soluble phenolic content in bog vs. fen pore-water. Together, these findings suggest that soluble phenolics could contribute to bogs’ extraordinary recalcitrance and high (relative to other peatland habitats) CO₂:CH₄ production ratios.

Improving cellulases hydrolytic action: An expanded role for electron donors of lytic polysaccharide monooxygenases in cellulose saccharification

Ascorbic acid (AscA) and gallic acid (GalA) are common electron donors and their boosting effect on lytic polysaccharide monooxygenases (LPMO) has been studied extensively. However, their influence on cellulase hydrolytic action has been ignored. In this work, the effect of AscA and GalA on cellulases hydrolytic action was evaluated. It was found that AscA could increase the hydrolysis of cellulose by cellulases, while GalA showed no effect on cellulases' hydrolytic action. The effect of AscA differed for the monocomponent cellulases: it showed a special boosting effect on cellobiohydrolase, rather than endoglucanase and β-glucosidase. This promoting effect could be another mechanism behind the boosting effect of the AscA-driven LPMO system on cellulose saccharification. These findings thus advance the understanding of the role of electron donors on cellulose saccharification and offer important clues on how to evaluate the feasibility of electron donors from a new perspective.

Identifying the negative cooperation between major inhibitors of cellulase activity and minimizing their inhibitory potential during hydrolysis of acid-pretreated corn stover

Soluble compounds produced during the enzymatic hydrolysis of lignocelluloses hampers cellulose conversion. Cellobiose and vanillin most severely inhibited the effect of cellobiohydrolase I. A concentration-dependent negative cooperative effect was found between cellobiose and vanillin. The combined inhibitory effect was about 83.5% of the cellobiose and 88.1% of the vanillin when their concentration was 20 mg/ml. However, the negative synergy could be eliminated by excessive enzyme loading. Differences in their binding sites on the catalytic domain of cellobiohydrolase I lead to negative synergistic inhibition, which should be considered in devising strategies to alleviate this effect. Combined β-glucosidase and PEG addition at an appropriate dose was feasible to balance cost and hydrolytic efficiency. To achieve efficient hydrolysis, especially at high solid concentrations, it is important to understand the synergistic inhibition between these inhibitors.

New approach to the evaluation of lignocellulose derived by-products impact on lytic-polysaccharide monooxygenase activity by using molecular descriptor structural causality model

Lytic-polysaccharide monooxygenase (LPMO) is one of the most important enzyme involved in biocatalytic lignocellulose degradation, and therefore inhibition of LPMO has significant effects on all related processes. Structural causality model (SCM) were established to evaluate impact of phenolic by-products in lignocellulose hydrolysates on LPMO activity. The molecular descriptors GATS4c, ATS2m, BIC3 and VR2_Dzs were found to be significant in describing inhibition. The causalities of the molecular descriptors and LPMO activity are determined by evaluating the directed acyclic graph (DAG) and the d-separation algorithm. The maximum causality for LPMO activation is β = 0.79 by BIC3 and the maximum causality of inhibition is β = -0.56 for the GATS4c descriptor. The model has the potential to predict the inhibition of LPMO and its application could be useful in selecting an appropriate lignocellulose pretreatment method to minimise the production of a potent inhibitor. This will subsequently lead to more efficient lignocellulose degradation process.

Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

Enzymatic hydrolysis of lignocellulose for bioethanol production shows a great potential to remit the rapid consumption of fossil fuels, given the fact that lignocellulose feedstocks are abundant, cost-efficient, and renewable. Lignin results in low enzymatic saccharification by forming the steric hindrance, non-productive adsorption of cellulase onto lignin, and deactivating the cellulase. In general, the non-productive binding of cellulase on lignin is widely known as the major cause for inhibiting the enzymatic hydrolysis. Pretreatment is an effective way to remove lignin and improve the enzymatic digestibility of lignocellulose. Along with removing lignin, the pretreatment can modify the lignin structure, which significantly affects the non-productive adsorption of cellulase onto lignin. To relieve the inhibitory effect of lignin on enzymatic hydrolysis, enormous efforts have been made to elucidate the correlation of lignin structure with lignin-enzyme interactions but with different views. In addition, contrary to the traditional belief that lignin inhibits enzymatic hydrolysis, in recent years, the addition of water-soluble lignin such as lignosulfonate or low molecular-weight lignin exerts a positive effect on enzymatic hydrolysis, which gives a new insight into the lignin-enzyme interactions. For throwing light on their structure-interaction relationship during enzymatic hydrolysis, the effect of residual lignin in substrate and introduced lignin in hydrolysate on enzymatic hydrolysis are critically reviewed, aiming at realizing the targeted regulation of lignin structure for improving the saccharification of lignocellulose. The review is also focused on exploring the lignin-enzyme interactions to mitigate the negative impact of lignin and reducing the cost of enzymatic hydrolysis of lignocellulose.

Net Energy Analysis and Techno-Economic Assessment of Co-Production of Bioethanol and Biogas from Cellulosic Biomass

Co-production is a process based on the biorefinery concept that maximizes the benefit of biomass by reusing residue from the production of one product to produce others. In this regard, biogas is one of the most researched second products for the production of ethanol from cellulosic biomass. However, operating this scheme requires additional investment in biogas processing equipment. This review compiles data from research studies on the co-production of bioethanol and biogas from lignocellulosic biomass to determine which is more worthwhile: leaving the residue or investing more to benefit from the second product. According to previous research, ethanol stillage can be converted to biogas via anaerobic digestion, increasing energy output by 2–3 fold. Techno-economic studies demonstrated that the co-production process reduces the minimum ethanol selling price to a level close to the market price of ethanol, implying the possibility of industrializing cellulosic ethanol production through this scheme.

Microbial population genomes from the Amazon River reveal possible modulation of the organic matter degradation process in tropical freshwaters

Rivers connect the carbon cycle in land with that in aquatic ecosystems by transporting and transforming terrestrial organic matter (TeOM). The Amazon River receives huge loads of TeOM from the surrounding rainforest, promoting a substantial microbial heterotrophic activity and consequently, CO₂ outgassing. In the Amazon River, microbes degrade up to 55% of the lignin present in the TeOM. Yet, the main microbial genomes involved in TeOM degradation were unknown. Here, we characterize 51 population genomes (PGs) representing some of the most abundant microbes in the Amazon River deriving from 106 metagenomes. The 51 reconstructed PGs are among the most abundant microbes in the Amazon River, and 53% of them are not able to degrade TeOM. Among the PGs capable of degrading TeOM, 20% were exclusively cellulolytic, while the others could also oxidize lignin. The transport and consumption of lignin oxidation byproducts seemed to be decoupled from the oxidation process, being apparently performed by different groups of microorganisms. By connecting the genomic features of abundant microbes in the Amazon River with the degradation machinery of TeOM, we suggest that a complex microbial consortium could explain the quick turnover of TeOM previously observed in this ecosystem.

Highly-toughened PVA/nanocellulose hydrogels with anti-oxidative and antibacterial properties triggered by lignin-Ag nanoparticles

In this study, Ag nanoparticles were firstly reduced on the surface of lignin nanoparticles (LNP_Ag) by direct reaction of silver nitrate without the use of a catalyst. Thermogravimetric analysis, Zeta potential and transmission electron microscopy measurements were performed to give evidence of the effectiveness of the reaction. After that, glutaraldehyde crosslinked PVA hydrogels, were produced by addition of unmodified LNP and Ag loaded LNP (LNP_Ag) in presence of cellulose nanocrystals (CNC). Thermal, mechanical, rheological, microstructural and biological anti-oxidative and anti-bacterial properties of the resulted hydrogels were investigated. It was proved that all the three nanofillers were homogeneously dispersed in PVA, and the pore diameter of the hydrogels was in the range of 0.5-2.0 μm. Nevertheless, the hydrogels showed high toughness, long-term and repeatable adhesiveness to a variety of substrates. In particular, composite hydrogels containing LNP_Ag nanoparticles showed excellent radical scavenging and antibacterial activities. Consequently, the effects of PVA-2CNC-2LNP_Ag on wound healing in mice model of full-thickness skin resection were evaluated by hematoxylin and eosin staining, taking as a reference the PVA-2CNC-2LNP system. The results showed that the wound healing time of PVA-2CNC-2LNP_Ag group was faster than that of neat PVA and PVA-2CNC, highlighting the role of LNP_Ag in enhancing the contact-active anti-oxidative and antibacterial activities mechanism in composite hydrogels. We expected that PVA hydrogels incorporating LNP_Ag could be used as green and efficient biomedical wound dressing materials.

Impact of phenolic compound as activators or inhibitors on the enzymatic hydrolysis of cellulose

The influence of phenolic compounds on the enzymatic hydrolysis of cellulose was studied in depth using spectrophotometric techniques, adsorption analysis and Scanning Electron Microscopy (SEM). In this paper for the first time, both possible interactions between phenolic compounds and the enzyme or the substrate were investigated, with the use of various phenolic compounds, cellulase from T. reesei, and Avicel as cellulose source. Three classes of phenolic compounds have been identified, based on their effect on the hydrolysis of cellulose: inhibitors (quercetin, kaempferol, trans-cinnamic acid, luteolin, ellagic acid), non-inhibitors (p-coumaric acid, rutin, caffeic acid), and activators (ferulic acid, syringic acid, sinapic acid, vanillic acid). Secondly, since various structures of phenolic compounds were tested, a structure - action comprehensive correlation was possible leading to the conclusion that an -OCH₃ group was necessary for the activating effect. Finally, based on the adsorption spectra and unique SEM images, a different way of adsorption (either on the enzyme or on the substrate) was noticed, depending on the activating or inhibiting action of the phenolic compound.

Current understanding of the inhibition factors and their mechanism of action for the lignocellulosic biomass hydrolysis

Biorefining of lignocellulosic biomass is a relatively new concept but it has strong potential to develop and partially replace the fossil derived fuels and myriad of value products to subsequently reduce the greenhouse gas emissions. However, the energy and cost intensive process of releasing the entrapped fermentable sugars is a major challenge for its commercialization. Various factors playing a detrimental role during enzymatic hydrolysis of biomass are inherent recalcitrance of lignocellulosic biomass, expensive enzymes, sub-optimal enzyme composition, lack of synergistic activity and enzyme inhibition caused by various inhibitors. The current study investigated the mechanism of enzyme inhibition during lignocellulosic biomass saccharification especially at high solid loadings. These inhibition factors are categorized into physio-chemical factors, water-soluble and -insoluble enzyme inhibitors, oligomers and enzyme-lignin binding. Furthermore, different approaches are proposed to alleviate the challenges and improve the enzymatic hydrolysis efficiency such as supplementation with surfactants, synergistic catalytic/non-catalytic proteins, and bioprocess modifications.

A multiplexed nanostructure-initiator mass spectrometry (NIMS) assay for simultaneously detecting glycosyl hydrolase and lignin modifying enzyme activities

Lignocellulosic biomass is composed of three major biopolymers: cellulose, hemicellulose and lignin. Analytical tools capable of quickly detecting both glycan and lignin deconstruction are needed to support the development and characterization of efficient enzymes/enzyme cocktails. Previously we have described nanostructure-initiator mass spectrometry-based assays for the analysis of glycosyl hydrolase and most recently an assay for lignin modifying enzymes. Here we integrate these two assays into a single multiplexed assay against both classes of enzymes and use it to characterize crude commercial enzyme mixtures. Application of our multiplexed platform based on nanostructure-initiator mass spectrometry enabled us to characterize crude mixtures of laccase enzymes from fungi Agaricus bisporus (Ab) and Myceliopthora thermophila (Mt) revealing activity on both carbohydrate and aromatic substrates. Using time-series analysis we determined that crude laccase from Ab has the higher GH activity and that laccase from Mt has the higher activity against our lignin model compound. Inhibitor studies showed a significant reduction in Mt GH activity under low oxygen conditions and increased activities in the presence of vanillin (common GH inhibitor). Ultimately, this assay can help to discover mixtures of enzymes that could be incorporated into biomass pretreatments to deconstruct diverse components of lignocellulosic biomass.

Enhancing the Radical Scavenging Activity and UV Resistance of Lignin Nanoparticles via Surface Mannich Amination toward a Biobased Antioxidant

In recent years, lignin specific activities, such as antioxidation and antibacterial and anti-ultraviolet performance, have drawn more and more attention. Nevertheless, the insufficient radical scavenging (antioxidation) activity has become one of the main drawbacks that limits its high-value application. In this study, lignin nanoparticles (LNPs) were prepared via a facile acid treatment strategy. Subsequently, surface amination of LNPs (a-LNPs) was carried out through the Mannich reaction. Specifically, the antioxidant behavior of LNPs and modified LNPs was evaluated by DPPH/DMPO radical scavenging and in vitro HeLa cell reactive oxygen species (ROS) scavenging tests, which demonstrated that the antioxidation activity of a-LNPs was more evident than that of both LNPs and butylated hydroxytoluene (BHT) commercial antioxidant. The mechanism of the radical scavenging ability of aminated LNPs was elucidated and proved to be related to the bond dissociation enthalpy of Ar-O···H, determined by the electron-donating effect of the substituted groups in the ortho-position. Meanwhile, the morphologies, solubilities, and UV-absorbing and antibacterial behavior of LNPs and a-LNPs were also studied, and the results showed that a-LNP sample exhibited higher UV resistance performance than LNPs. We expected that the modified LNPs with high antioxidation activity can serve as a safe and lower-cost biobased antioxidant.

UV Protective, Antioxidant, Antibacterial and Compostable Polylactic Acid Composites Containing Pristine and Chemically Modified Lignin Nanoparticles

Polylactic acid (PLA) films containing 1 wt % and 3 wt % of lignin nanoparticles (pristine (LNP), chemically modified with citric acid (caLNP) and acetylated (aLNP)) were prepared by extrusion and characterized in terms of their overall performance as food packaging materials. Morphological, mechanical, thermal, UV–Vis barrier, antioxidant and antibacterial properties were assayed; appropriate migration values in food simulants and disintegration in simulated composting conditions were also verified. The results obtained indicated that all lignin nanoparticles succeeded in conferring UV-blocking, antioxidant and antibacterial properties to the PLA films, especially at the higher filler loadings assayed. Chemical modification of the fillers partially reduced the UV protection and the antioxidant properties of the resulting composites, but it induced better nanoparticles dispersion, reduced aggregates size, enhanced ductility and improved aesthetic quality of the films through reduction of the characteristic dark color of lignin. Migration tests and disintegration assays of the nanocomposites in simulated composting conditions indicated that, irrespectively of their formulation, the multifunctional nanocomposite films prepared behaved similarly to neat PLA.

Design strategies, properties and applications of cellulose nanomaterials-enhanced products with residual, technical or nanoscale lignin-A review

With the increasing demand for greener alternatives to fossil-derived products, research on cellulose nanomaterials (CNMs) has rapidly expanded. The combination of nanoscale properties and sustainable attributes makes CNMs an asset in the quest for a sustainable society. However, challenges such as the hydrophilic nature of CNMs, their low compatibility with non-polar matrices and modest thermal stability, slow the development of end-uses. Combination of CNMs with amphiphilic lignin can improve the thermal stability, enhance the compatibility with non-polar matrices and, additionally, endow CNMs with new functionalities e.g., UV shielding or antioxidative properties. This article comprehensively reviews the different design strategies and their influence on properties and applications of CNMs containing lignin in various forms; either as residual lignin, added technical lignin, or nanoscale particles. The review focuses especially on the synergy created between CNMs and lignin, paving the way for new production routes and use of CNM/lignin materials in high-performance applications.

Uncovering the genomic potential of the Amazon River microbiome to degrade rainforest organic matter

BACKGROUND

The Amazon River is one of the largest in the world and receives huge amounts of terrestrial organic matter (TeOM) from the surrounding rainforest. Despite this TeOM is typically recalcitrant (i.e. resistant to degradation), only a small fraction of it reaches the ocean, pointing to a substantial TeOM degradation by the river microbiome. Yet, microbial genes involved in TeOM degradation in the Amazon River were barely known. Here, we examined the Amazon River microbiome by analysing 106 metagenomes from 30 sampling points distributed along the river.

RESULTS

We constructed the Amazon River basin Microbial non-redundant Gene Catalogue (AMnrGC) that includes ~ 3.7 million non-redundant genes, affiliating mostly to bacteria. We found that the Amazon River microbiome contains a substantial gene-novelty compared to other relevant known environments (rivers and rainforest soil). Genes encoding for proteins potentially involved in lignin degradation pathways were correlated to tripartite tricarboxylates transporters and hemicellulose degradation machinery, pointing to a possible priming effect. Based on this, we propose a model on how the degradation of recalcitrant TeOM could be modulated by labile compounds in the Amazon River waters. Our results also suggest changes of the microbial community and its genomic potential along the river course.

CONCLUSIONS

Our work contributes to expand significantly our comprehension of the world's largest river microbiome and its potential metabolism related to TeOM degradation. Furthermore, the produced gene catalogue (AMnrGC) represents an important resource for future research in tropical rivers. Video abstract.