Phenols and lignin: Key players in reducing enzymatic hydrolysis yields of steam-pretreated biomass in presence of laccase

Are phenolic compounds produced during the enzymatic production of prebiotic xylooligosaccharides (XOS) beneficial: a review

Phenolics produced during xylooligosaccharide production might inhibit xylanases and enhance the antioxidant and antimicrobial activities of XOS. The effects of phenolic compounds on xylanases may depend on the type and concentration of the compound, the plant biomass used, and the enzyme used. Understanding the effects of phenolic compounds on xylanases and their impact on XOS is critical for developing viable bioconversion of lignocellulosic biomass to XOS. Understanding the complex relationship between phenolic compounds and xylanases can lead to the development of strategies that improve the efficiency and cost-effectiveness of XOS manufacturing processes and optimise enzyme performance.

Effects of Lignin-Diverted Reductant with Polyphenol Oxidases on Cellulose Degradation by Wild and Mutant Types of Lytic Polysaccharide Monooxygenase

Establishing a multi-enzyme synergistic lignocellulosic biodegradation system using lytic polysaccharide monooxygenase (LPMO) and polyphenol oxidases is vital for efficiently utilizing plant biomass waste, ultimately benefiting the carbon cycle and promoting environmental protection. Single-residue mutations of LPMO can improve the efficiency of lignocellulosic biomass degradation. However, the activity of mutant-type LPMO in relation to lignin-diverted reducing agents has not been sufficiently explored. In this study, laccase and tyrosinase were initially investigated and their optimal conditions and impressive thermal stability were revealed, indicating their potential synergistic abilities with LPMO in lignocellulose biodegradation. When utilizing gallic acid as a reducing agent, the activities of LPMOs were increased by over 10%, which was particularly evident in mutant-type LPMOs after the addition of polyphenol oxidases. In particular, the combination of tyrosinase with either 4-hydroxy-3-methoxyphenylacetone or p-coumaric acid was shown to enhance the efficacy of LPMOs. Furthermore, the highest activity levels of wild-type LPMOs were observed with the addition of laccase and 3-methylcatechol. The similarities between wild and mutant LPMOs regarding their activities in lignin-diverted phenolic compounds and reducing agents are almost identical, suggesting that the single-residue mutation of LPMO does not have a detrimental effect on its performance. Above all, this study indicates that understanding the performance of both wild and mutant types of LPMOs in the presence of polyphenol oxidases and various reducing agents constitutes a key link in the industrialization of the multi-enzyme degradation of lignocellulose.

Preparation and characterization of bacterial cellulose synthesized by kombucha from vinegar residue

Bacterial cellulose (BC) has been widely applied in various fields due to its excellent physicochemical properties, but its high production cost remains a challenge. Herein, the present study aimed to utilize the hydrolysate of vinegar residue (VR) as the only medium to realize the cost-effective production of BC. The BC production was optimized by the single-factor test. The treatment of 6 % VR concentration with 3 % acid concentration at 100 °C for 1.5 h and 96 U/mL of cellulase for 4 h at 50 °C obtained a maximum reducing sugar concentration of about 32 g/L. Additionally, the VR hydrolysate treated with 3 % active carbon (AC) at 40 °C for 0.5 h achieved a total phenol removal ratio of 86 %. The yield of BC reached 2.1 g/L under the optimum conditions, which was twice compared to the standard medium. The produced BC was characterized by SEM, FT-IR, XRD, and TGA analyses, and the results indicated that the BC prepared by AC-treated VR hydrolysate had higher fiber density, higher crystallinity, and good thermal stability. Furthermore, the regenerated BC (RBC) fibers with a tensile stress of 400 MPa were prepared successfully using AmimCl solution as a solvent by dry-wet-spinning method. Overall, the VR waste could be used as an alternative carbon source for the sustainable production of BC, which could be further applied to RBC fibers preparation.

Effects of laccase and cellulase on saccharification of barley malt

Improving saccharification of barley malt is beneficial to promoting economic benefits of beer brewers, but there are few detailed reports on the application of cellulase and laccase in barley malt. So, barley malt was pretreated by cellulase and laccase, and the malt wort and brewer's spent grains were analyzed by HPLC, FTIR and SEM in this study. The concentration of malt wort was increased significantly to 8.1 (° Bx), which increased by 28.6% after barley malt was pretreated by cellulase, but laccase could not improve saccharification of barley malt. Through analysis of sugar in malt wort and cellulose and lignin components as well as physical and chemical structures of brewer's spent grains, the increase in sugar content in malt wort was mainly due to the increase in glucose because of hydrolysis of cellulose in barley malt by cellulase. Furtherly, laccase and cellulase should have a mutual inhibition when they are pretreated simultaneously.

Bacterial cellulose/lignin nanoparticles composite films with retarded biodegradability

In practical applications, the full biodegradability of all-biomass-based bacterial cellulose (BC) composites enhances their environmentally friendliness but results in the poor durability especially at humid conditions. This work prepared BC/lignin nanoparticles (LNPs) composite films with retarded biodegradability, which could broaden their application area. Three LNPs were fabricated using technical lignins extracted by deep eutectic solvent (DES), ethanol organosolv, soda/anthraquinone from poplar. LNPs involvement during BC fermentation showed limited influence on its productivity but significantly retarded the biodegradation of composite films. The potential inhibition mechanism was physical barrier and non-productive binding of LNPs. The BC/Soda LNPs showed much higher retarded degradation property (~58 wt% degradation) compared to BC/Organosolv LNPs and BC/DES LNPs (~85 wt% and ~ 97 wt% degradation respectively) at high enzyme loadings of 5 mg g^-1 BCE. While at low enzyme loadings of 1 mg g^-1 BCE, all these three composite films showed comparable retarded degradation property of ~60 wt%.

Production of Cellulosic Ethanol from Enzymatically Hydrolysed Wheat Straws

The aim of this study is to find the optimal pretreatment conditions and hydrolysis in order to obtain a high yield of bioethanol from wheat straw. The pretreatments were performed with different concentrations of sulphuric acid 1, 2 and 3% (v/v), and were followed by an enzymatic hydrolysis that was performed by varying the solid-to-liquid ratio (1/20, 1/25 and 1/30 g/mL) and the enzyme dose (30/30 µL/g, 60/60 µL/g and 90/90 µL/g Viscozyme® L/Celluclast® 1.5 L). This mix of enzymes was used for the first time in the hydrolysis process of wheat straws which was previously pretreated with dilute sulfuric acid. Scanning electron microscopy indicated significant differences in the structural composition of the samples because of the pretreatment with H2SO4 at different concentrations, and ATR-FTIR analysis highlighted the changes in the chemical composition in the pretreated wheat straw as compared to the untreated one. HPLC-RID was used to identify and quantify the carbohydrates content resulted from enzymatic hydrolysis to evaluate the potential of using wheat straws as a raw material for production of cellulosic ethanol in Romania. The highest degradation of lignocellulosic material was obtained in the case of pretreatment with 3% H2SO4 (v/v), a solid-to-liquid ratio of 1/30 and an enzyme dose of 90/90 µL/g. Simultaneous saccharification and fermentation were performed using Saccharomyces cerevisiae yeast, and for monitoring the fermentation process a BlueSens equipment was used provided with ethanol, O2 and CO2 cap sensors mounted on the fermentation flasks. The highest concentration of bioethanol was obtained after 48 h of fermentation and it reached 1.20% (v/v).

Application of enzymatic and bacterial biodelignification systems for enhanced breakdown of model lignocellulosic wastes

This paper explores the extent to which enzymatic and bacterial biodelignification systems can breakdown lignocellulose in model wastes to potentially enhance biogas generation. Two representative lignocellulosic wastes (newspaper and softwood) commonly found largely undegraded in old landfills were used. A fungal peroxidase (lignin peroxidase) enzyme and a recently isolated lignin-degrading bacterial strain (Agrobacterium sp.) were used. Tests were conducted in stirred bioreactors with methanogens from sewage sludge added to produce biogas from breakdown products. Addition of lignin peroxidase resulted in ~20% enhancement in cumulative methane produced in newspaper reactors. It had a negative effect on wood. Agrobacterium sp. strain enhanced biodegradation of both wood (~20% higher release of soluble organic carbon and enhanced breakdown) and newspaper (~2-fold biogas yield). The findings of this paper have important implications for enhanced breakdown in old landfills that are rich in these wastes, and anaerobic operations utilising lignocellulosic wastes for higher degradation efficiencies and biogas production.

Understanding the structural characteristics of water-soluble phenolic compounds from four pretreatments of corn stover and their inhibitory effects on enzymatic hydrolysis and fermentation

BACKGROUND

For bioethanol production from lignocellulosic biomass, phenolics derived from pretreatment have been generally considered as highly inhibitory towards enzymatic hydrolysis and fermentation. As phenolics are produced from lignin degradation during pretreatment, it is likely that the pretreatment will exert a strong impact on the structure of phenolics, resulting in varied levels of inhibition of the bioconversion process. Despite the extensive studies on pretreatment, it remains unclear how pretreatment process affects the properties of generated phenolics and how the inhibitory effect of phenolics from different pretreatment varies on enzymatic hydrolysis and fermentation.

RESULTS

In this study, the structural properties of phenolic compounds derived from four typical pretreatment [dilute acid (DA), liquid hot water pretreatment (LHW), ammonia fiber expansion (AFEX) and alkaline pretreatment (AL)] were characterized, and their effect on both enzymatic hydrolysis and fermentation were evaluated. The inhibitory effect of phenolics on enzymatic hydrolysis followed the order: AFEX > LHW > DA > AL, while the inhibitory effect of phenolics on Zymomonas mobilis 8b strain fermentation followed the order: AL > LHW > DA > AFEX. Interestingly, this study revealed that phenolics derived from AFEX showed more severe inhibitory effect on enzymatic hydrolysis than those from the other pretreatments at the same phenolics concentrations (note: AFEX produced much less amount of phenolics compared to AL and DA), while they exhibited the lowest inhibitory effect on fermentation. The composition of phenolics from different pretreatments was analyzed and model phenolics were applied to explore the reason for this difference. The results suggested that the amide group in phenolics might account for this difference.

CONCLUSIONS

Pretreatment process greatly affects the properties of generated phenolics and the inhibitory effects of phenolics on enzymatic hydrolysis and fermentation. This study provides new insight for further pretreatment modification and hydrolysate detoxification to minimize phenolics-caused inhibition and enhance the efficiency of enzymatic hydrolysis and fermentation.

Constraints and advances in high-solids enzymatic hydrolysis of lignocellulosic biomass: a critical review

The industrial production of sugar syrups from lignocellulosic materials requires the conduction of the enzymatic hydrolysis step at high-solids loadings (i.e., with over 15% solids [w/w] in the reaction mixture). Such conditions result in sugar syrups with increased concentrations and in improvements in both capital and operational costs, making the process more economically feasible. However, this approach still poses several technical hindrances that impact the process efficiency, known as the "high-solids effect" (i.e., the decrease in glucan conversion yields as solids load increases). The purpose of this review was to present the findings on the main limitations and advances in high-solids enzymatic hydrolysis in an updated and comprehensive manner. The causes for the rheological limitations at the onset of the high-solids operation as well as those influencing the "high-solids effect" will be discussed. The subject of water constraint, which results in a highly viscous system and impairs mixing, and by extension, mass and heat transfer, will be analyzed under the perspective of the limitations imposed to the action of the cellulolytic enzymes. The "high-solids effect" will be further discussed vis-à-vis enzymes end-product inhibition and the inhibitory effect of compounds formed during the biomass pretreatment as well as the enzymes' unproductive adsorption to lignin. This review also presents the scientific and technological advances being introduced to lessen high-solids hydrolysis hindrances, such as the development of more efficient enzyme formulations, biomass and enzyme feeding strategies, reactor and impeller designs as well as process strategies to alleviate the end-product inhibition. We surveyed the academic literature in the form of scientific papers as well as patents to showcase the efforts on technological development and industrial implementation of the use of lignocellulosic materials as renewable feedstocks. Using a critical approach, we expect that this review will aid in the identification of areas with higher demand for scientific and technological efforts.

Novel redox-active enzymes for ligninolytic applications revealed from multiomics analyses of Peniophora sp. CBMAI 1063, a laccase hyper-producer strain

The repertoire of redox-active enzymes produced by the marine fungus Peniophora sp. CBMAI 1063, a laccase hyper-producer strain, was characterized by omics analyses. The genome revealed 309 Carbohydrate-Active Enzymes (CAZymes) genes, including 48 predicted genes related to the modification and degradation of lignin, whith 303 being transcribed under cultivation in optimized saline conditions for laccase production. The secretome confirmed that the fungus can produce a versatile ligninolytic enzyme cocktail. It secretes 56 CAZymes, including 11 oxidative enzymes classified as members of auxiliary activity families (AAs), comprising two laccases, Pnh_Lac1 and Pnh_Lac2, the first is the major secretory protein of the fungi. The Pnh_Lac1-mediator system was able to promote the depolymerization of lignin fragments and polymeric lignin removal from pretreated sugarcane bagasse, confirming viability of this fungus enzymatic system for lignocellulose-based bioproducts applications.

Deciphering the molecular specificity of phenolic compounds as inhibitors or glycosyl acceptors of β-fructofuranosidase from Xanthophyllomyces dendrorhous

Enzymatic glycosylation of polyphenols is a tool to improve their physicochemical properties and bioavailability. On the other hand, glycosidic enzymes can be inhibited by phenolic compounds. In this work, we studied the specificity of various phenolics (hydroquinone, hydroxytyrosol, epigallocatechin gallate, catechol and p-nitrophenol) as fructosyl acceptors or inhibitors of the β-fructofuranosidase from Xanthophyllomyces dendrorhous (pXd-INV). Only hydroquinone and hydroxytyrosol gave rise to the formation of glycosylated products. For the rest, an inhibitory effect on both the hydrolytic (H) and transglycosylation (T) activity of pXd-INV, as well as an increase in the H/T ratio, was observed. To disclose the binding mode of each compound and elucidate the molecular features determining its acceptor or inhibitor behaviour, ternary complexes of the inactive mutant pXd-INV-D80A with fructose and the different polyphenols were analyzed by X-ray crystallography. All the compounds bind by stacking against Trp105 and locate one of their phenolic hydroxyls making a polar linkage to the fructose O2 at 3.6–3.8 Å from the C2, which could enable the ulterior nucleophilic attack leading to transfructosylation. Binding of hydroquinone was further investigated by soaking in absence of fructose, showing a flexible site that likely allows productive motion of the intermediates. Therefore, the acceptor capacity of the different polyphenols seems mediated by their ability to make flexible polar links with the protein, this flexibility being essential for the transfructosylation reaction to proceed. Finally, the binding affinity of the phenolic compounds was explained based on the two sites previously reported for pXd-INV.

Bio-detoxification Bacteria Isolated from Dye-Polluted Soils Promote Lactic Acid Production from Ammonia Pretreated Corn Stover

Agro-stovers are the most abundant substrates for producing lactic acid, which has great potential application in the production of biodegradable and biocompatible polylactic acid polymers. However, chemical pretreatments on agro-stovers generate inhibitors that repress the subsequent lactic acid fermentation. In this study, three bacterial strains (Enterococcus faecalis B101, Acinetobacter calcoaceticus C1, and Pseudomonas aeruginosa CS) isolated from dye-polluted soils could utilize phenolic inhibitor mimics (vanillin, 4- hydroxybenzaldehyde, or syringaldehyde) from alkaline pretreated corn stovers as a sole carbon source. Lactic acid titer increased from 27.42 g/L (Bacillus coagulans LA204 alone) to 44.76 g/L (CS and LA204) using 50 g/L glucose with 1 g/L 4-hydroxybenzaldehyde added. Lactic acid production from 50 g/L ammonia pretreated corn stover was increased nearly twofold by inoculating phenolic degradation bacteria and lactic acid bacteria (C1& Lactobacillus pentosus FL0421). In the control (FL0421 alone), only 16.98 g/L of lactic acid was produced. The isolated and identified strains degraded the phenolic compounds and increased the lactic acid production from glucose and ammonia pretreated corn stover. These characteristics of the strains support industrial application with efficient in situ detoxification of phenolic compounds during lactic acid production from agro-stovers using simultaneous saccharification and fermentation (SSF).

A thermostable laccase from Thermus sp. 2.9 and its potential for delignification of Eucalyptus biomass

Laccases are multicopper oxidases that are being studied for their potential application in pretreatment strategies of lignocellulosic feedstocks for bioethanol production. Here, we report the expression and characterization of a predicted laccase (LAC_2.9) from the thermophilic bacterial strain Thermus sp. 2.9 and investigate its capacity to delignify lignocellulosic biomass. The purified enzyme displayed a blue color typical of laccases, showed strict copper dependence and retained 80% of its activity after 16 h at 70 °C. At 60 °C, the enzyme oxidized 2,2′-azino-di-(3-ethylbenzthiazoline sulfonate) (ABTS) and 2,6-dimethoxyphenol (DMP) at optimal pH of 5 and 6, respectively. LAC_2.9 had higher substrate specificity (k_cat/K_M) for DMP with a calculated value that accounts for one of the highest reported for laccases. Further, the enzyme oxidized a phenolic lignin model dimer. The incubation of steam-exploded eucalyptus biomass with LAC_2.9 and 1-hydroxybenzotriazole (HBT) as mediator changed the structural properties of the lignocellulose as evidenced by Fourier transform infrared (FTIR) spectroscopy and thermo-gravimetric analysis (TGA). However, this did not increase the yield of sugars released by enzymatic saccharification. In conclusion, LAC_2.9 is a thermostable laccase with potential application in the delignification of lignocellulosic biomass.

Laccase-derived lignin compounds boost cellulose oxidative enzymes AA9

BACKGROUND

The discovery of lignin as activator for the redox enzyme lytic polysaccharide monooxygenases (LPMOs) for the oxidation of cell-wall polysaccharides opens a new scenario for investigation of the interplay between different lignocellulose-degrading enzymes. The lignin-active enzymes in one hand, and the carbohydrate active in the other, are linked through a variety of electrons carrier molecules either derived from lignin or enzymatically transferred. Likewise, in nature, many lignocellulose-degrading organisms are expressing those enzymes simultaneously, and we wanted to test if a major commercial available lignin oxidase enzyme, i.e., laccase could benefit and synergize the activity of the LPMOs by depolymerizing the insoluble lignin.

RESULTS

In this work, two fungal laccases together with a mediator (ABTS) were used to isolate low-molecular-weight lignin from lignocellulosic biomass. The isolated lignins were used as electron donors for activation of LPMOs. A direct correlation between the low-molecular-weight lignin isolated with laccases and an increased activity of a cellulolytic cocktail containing LPMO was found when pure cellulose was hydrolyzed. We then tried to implement existing commercial cellulases cocktail with laccase enzymes, but under the conditions tested, the co-incubation of laccases with LPMOs showed a substrate competition towards oxygen inhibiting the LPMO. In addition, we found that laccase treatment may cause other modifications to pure cellulose, rendering the material more recalcitrant for enzymatic saccharification.

CONCLUSIONS

Laccase-mediated system was able to depolymerize lignin from pre-treated and native sugarcane bagasse and wheat straw, and the released phenolic molecules were able to donate electrons to LPMO enzymes boosting the overall enzymatic hydrolysis of cellulose. Likewise, other poly-phenol oxidase, we might have just started showing possible pros or cons in applying several oxidase enzymes for a simultaneous degradation of cellulose and lignin, and we found that the competition towards oxygen and their different consumption rates must be taken into account for any possible co-application.

Comparison of the efficiency of bacterial and fungal laccases in delignification and detoxification of steam-pretreated lignocellulosic biomass for bioethanol production

This study evaluates the potential of a bacterial laccase from Streptomyces ipomoeae (SilA) for delignification and detoxification of steam-exploded wheat straw, in comparison with a commercial fungal laccase from Trametes villosa. When alkali extraction followed by SilA laccase treatment was applied to the water insoluble solids fraction, a slight reduction in lignin content was detected, and after a saccharification step, an increase in both glucose and xylose production (16 and 6%, respectively) was observed. These effects were not produced with T. villosa laccase. Concerning to the fermentation process, the treatment of the steam-exploded whole slurry with both laccases produced a decrease in the phenol content by up to 35 and 71% with bacterial and fungal laccases, respectively. The phenols reduction resulted in an improved performance of Saccharomyces cerevisiae during a simultaneous saccharification and fermentation (SSF) process, improving ethanol production rate. This enhancement was more marked with a presaccharification step prior to the SSF process.

Laccase enzyme detoxifies hydrolysates and improves biogas production from hemp straw and miscanthus

The impact of various phenolic compounds, vanillic acid, ferulic acid, p-coumaric acid and 4-hydroxybenzoic acid on anaerobic digestion of lignocellulosic biomass (hemp straw and miscanthus) was studied. Such phenolic compounds have been known to inhibit biogas production during anaerobic digestion. The different phenolic compounds were added in various concentrations: 0, 100, 500, 1000 and 2000mg/L. A difference in inhibition of biomethane production between the phenolic compounds was noted. Hydrolysis rate, during anaerobic digestion of miscanthus was inhibited up to 50% by vanillic acid, while vanillic acid had no influence on the initial rate of biogas production during the anaerobic digestion of hemp straw. Miscanthus has a higher lignin concentration (12-30g/100gDM) making it less accessible for degradation, and in combination with phenolic compounds released after harsh pretreatments, it can cause severe inhibition levels during the anaerobic digestion, lowering biogas production. To counter the inhibition, lignin degrading enzymes can be used to remove or degrade the inhibitory phenolic compounds. The interaction of laccase and versatile peroxidase individually with the different phenolic compounds was studied to have insight in the polymerization of inhibitory compounds or breakdown of lignocellulose. Hemp straw and miscanthus were incubated with 0, 100 and 500mg/L of the different phenolic compounds for 0, 6 and 24h and pretreated with the lignin degrading enzymes. A laccase pretreatment successfully detoxified the substrate, while versatile peroxidase however was inhibited by 100mg/L of each of the individual phenolic compounds. Finally a combination of enzymatic detoxification and subsequent biogas production showed that a decrease in phenolic compounds by laccase treatment can considerably lower the inhibition levels of the biogas production.

Difference analysis of the enzymatic hydrolysis performance of acid-catalyzed steam-exploded corn stover before and after washing with water

The difference in the enzymatic hydrolysis yield of acid-catalyzed steam-exploded corn stover (ASC) before and after washing with water reached approximately 15 % under the same conditions. The reasons for the difference in the yield between ASC and washed ASC (wASC) were determined through the analysis of the composition of ASC prehydrolyzate and sugar concentration of enzymatic hydrolyzate. Salts produced by neutralization (CaSO4, Na2SO4, K2SO4, and (NH4)2SO4), sugars (polysaccharides, oligosaccharides, and monosaccharides), sugar-degradation products (weak acids and furans), and lignin-degradation products (ethyl acetate extracts and nine main lignin-degradation products) were back-added to wASC. Results showed that these products, except furans, exerted negative effect on enzymatic hydrolysis. According to the characteristics of acid-catalyzed steam explosion pretreatment, the five sugar-degradation products' mixture and salts [Na2SO4, (NH4)2SO4] showed minimal negative inhibition effect on enzymatic hydrolysis. By contrast, furans demonstrated a promotion effect. Moreover, soluble sugars, such as 13 g/L xylose (decreased by 6.38 %), 5 g/L cellobiose (5.36 %), 10 g/L glucose (3.67 %), as well as lignin-degradation products, and ethyl acetate extracts (4.87 %), exhibited evident inhibition effect on enzymatic hydrolysis. Therefore, removal of soluble sugars and lignin-degradation products could effectively promote the enzymatic hydrolysis performance.

Adaptor Scaffoldins: An Original Strategy for Extended Designer Cellulosomes, Inspired from Nature

Designer cellulosomes consist of chimeric cohesin-bearing scaffoldins for the controlled incorporation of recombinant dockerin-containing enzymes. The largest designer cellulosome reported to date is a chimeric scaffoldin that contains 6 cohesins. This scaffoldin represented a technical limit of sorts, since adding another cohesin proved problematic, owing to resultant low expression levels, instability (cleavage) of the scaffoldin polypeptide, and limited numbers of available cohesin-dockerin specificities—the hallmark of designer cellulosomes. Nevertheless, increasing the number of enzymes integrated into designer cellulosomes is critical, in order to further enhance degradation of plant cell wall material. Adaptor scaffoldins comprise an intermediate type of scaffoldin that can both incorporate various enzymes and attach to an additional scaffoldin. Using this strategy, we constructed an efficient form of adaptor scaffoldin that possesses three type I cohesins for enzyme integration, a single type II dockerin for interaction with an additional scaffoldin, and a carbohydrate-binding module for targeting to the cellulosic substrate. In parallel, we designed a hexavalent scaffoldin capable of connecting to the adaptor scaffoldin by the incorporation of an appropriate type II cohesin. The resultant extended designer cellulosome comprised 8 recombinant enzymes—4 xylanases and 4 cellulases—thereby representing a potent enzymatic cocktail for solubilization of natural lignocellulosic substrates. The contribution of the adaptor scaffoldin clearly demonstrated that proximity between the two scaffoldins and their composite set of enzymes is crucial for optimized degradation. After 72 h of incubation, the performance of the extended designer cellulosome was determined to be approximately 70% compared to that of native cellulosomes.

Plant cell wall residues represent a major source of renewable biomass for the production of biofuels such as ethanol via breakdown to soluble sugars. The natural microbial degradation process, however, is inefficient for achieving cost-effective processes in the conversion of plant-derived biomass to biofuels, either from dedicated crops or human-generated cellulosic wastes. The accumulation of the latter is considered a major environmental pollutant. The development of designer cellulosome nanodevices for enhanced plant cell wall degradation thus has major impacts in the fields of environmental pollution, bioenergy production, and biotechnology in general. The findings reported in this article comprise a true breakthrough in our capacity to produce extended designer cellulosomes via synthetic biology means, thus enabling the assembly of higher-order complexes that can supersede the number of enzymes included in a single multienzyme complex.