Cellulose Deconstruction Research Articles

Laboratory Evolution and Reverse Engineering of Clostridium thermocellum for Growth on Glucose and Fructose.

The native ability of Clostridium thermocellum to efficiently solubilize cellulose makes it an interesting platform for sustainable biofuel production through consolidated bioprocessing. Together with other improvements, industrial implementation of C. thermocellum, as well as fundamental studies into its metabolism, would benefit from improved and reproducible consumption of hexose sugars. To investigate growth of C. thermocellum on glucose or fructose, as well as the underlying molecular mechanisms, laboratory evolution was performed in carbon-limited chemostats with increasing concentrations of glucose or fructose and decreasing cellobiose concentrations. Growth on both glucose and fructose was achieved with biomass yields of 0.09 ± 0.00 and 0.18 ± 0.00 gbiomass gsubstrate-1, respectively, compared to 0.15 ± 0.01 gbiomass gsubstrate-1 for wild type on cellobiose. Single-colony isolates had no or short lag times on the monosaccharides, while wild type showed 42 ± 4 h on glucose and >80 h on fructose. With good growth on glucose, fructose, and cellobiose, the fructose isolates were chosen for genome sequence-based reverse metabolic engineering. Deletion of a putative transcriptional regulator (Clo1313_1831), which upregulated fructokinase activity, reduced lag time on fructose to 12 h with a growth rate of 0.11 ± 0.01 h-1 and resulted in immediate growth on glucose at 0.24 ± 0.01 h-1 Additional introduction of a G-to-V mutation at position 148 in cbpA resulted in immediate growth on fructose at 0.32 ± 0.03 h-1 These insights can guide engineering of strains for fundamental studies into transport and the upper glycolysis, as well as maximizing product yields in industrial settings.IMPORTANCEC. thermocellum is an important candidate for sustainable and cost-effective production of bioethanol through consolidated bioprocessing. In addition to unsurpassed cellulose deconstruction, industrial application and fundamental studies would benefit from improvement of glucose and fructose consumption. This study demonstrated that C. thermocellum can be evolved for reproducible constitutive growth on glucose or fructose. Subsequent genome sequencing, gene editing, and physiological characterization identified two underlying mutations with a role in (regulation of) transport or metabolism of the hexose sugars. In light of these findings, such mutations have likely (and unknowingly) also occurred in previous studies with C. thermocellum using hexose-based media with possible broad regulatory consequences. By targeted modification of these genes, industrial and research strains of C. thermocellum can be engineered to (i) reduce glucose accumulation, (ii) study cellodextrin transport systems in vivo, (iii) allow experiments at >120 g liter-1 soluble substrate concentration, or (iv) reduce costs for labeling studies.

Formic Acid Generation from Impregnated Cellulose with Iron Nanoparticles via Microwave-Assisted Processes

The enormous potential of formic acid (FA) as hydrogen carrier, high hydrogen content and low toxicity makes it a good alternative for hydrogen production. Direct generation of iron nanoparticles loosely incorporated in cellulose offered simple route to form FA. The presence of charged ions from alkali salt assisted in the deconstruction of cellulose to glucose and subsequent transformation of glucose to FA concentration of 0.47gC/L. Formic acid selectivity reached 15.8% at a reaction temperature of 180 °C. Employing iron nanoparticles and microwave process in FA production is an environmentally sustainable route. The above processes pave the way for lignocellulosic biomass usage for FA production and making economical usage of catalysts.

Cycling in degradation of organic polymers and uptake of nutrients by a litter-degrading fungus.

SummaryWood and litter degrading fungi are the main decomposers of lignocellulose and thus play a key role in carbon cycling in nature. Here, we provide evidence for a novel lignocellulose degradation strategy employed by the litter degrading fungus Agaricus bisporus (known as the white button mushroom). Fusion of hyphae allows this fungus to synchronize the activity of its mycelium over large distances (50 cm). The synchronized activity has a 13‐h interval that increases to 20 h before becoming irregular and it is associated with a 3.5‐fold increase in respiration, while compost temperature increases up to 2°C. Transcriptomic analysis of this burst‐like phenomenon supports a cyclic degradation of lignin, deconstruction of (hemi‐) cellulose and microbial cell wall polymers, and uptake of degradation products during vegetative growth of A. bisporus. Cycling in expression of the ligninolytic system, of enzymes involved in saccharification, and of proteins involved in nutrient uptake is proposed to provide an efficient way for degradation of substrates such as litter.

The current status of the enzyme-mediated isolation and functionalization of nanocelluloses: production, properties, techno-economics, and opportunities

The increasing interest for cellulose-based products has resulted in the development of processes for the controlled deconstruction of cellulose into cellulose nanomaterials, such as cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). These nanomaterials can significantly increase the diverse applications of cellulose by exploring their nanometric scale options and improved properties for various high-volume, low-volume, and emerging/novel applications. Among the nanocellulose production processes, the enzyme-mediated methods are environment friendly and with expected lower capital and operating expenditures compared to traditional processes. In addition, it creates the unique possibility of fine-tuning the process to tailor nanocellulose properties that are suitable for specific applications. This review comprehensively examines the application of enzymes in the isolation of nanocelluloses. To date, no enzyme preparation for application to nanocellulose production is available commercially. Therefore, a fundamental understanding of potential enzymes focusing mainly on their differentiated properties, mechanism and alterations promoted to cellulose at different levels is first provided. This is to shed light on the enzyme properties that can be exploited for application in nanocellulose isolation. Then, the current state of the stand-alone and integrated enzyme-mediated processes is reviewed as well as the properties and yield of the isolated nanocelluloses in comparison to nanocelluloses obtained by traditional processes. In addition, the potential of enzyme-mediated functionalization has been discussed as a promising method that imparts unique properties to nanocelluloses, further diversifying their market. A detailed discussion on the challenges and opportunities for the major technical and economic factors that impact nanocellulose price has been included as well.

A novel AA10 from Paenibacillus curdlanolyticus and its synergistic action on crystalline and complex polysaccharides.

Lytic polysaccharide monooxygenases (LPMOs) play an important role in the degradation of complex polysaccharides in lignocellulosic biomass. In the present study, we characterized a modular LPMO (PcAA10A), consisting of a family 10 auxiliary activity of LPMO (AA10) catalytic domain, and non-catalytic domains including a family 5 carbohydrate-binding module, two fibronectin type-3 domains, and a family 3 carbohydrate-binding module from Paenibacillus curdlanolyticus B-6, which was expressed in a recombinant Escherichia coli. Comparison of activities between full-length PcAA10A and the catalytic domain polypeptide (PcAA10A_CD) indicates that the non-catalytic domains are important for the deconstruction of crystalline cellulose and complex polysaccharides contained in untreated lignocellulosic biomass. Interestingly, PcAA10A_CD acted not only on cellulose and chitin, but also on xylan, mannan, and xylan and cellulose contained in lignocellulosic biomass, which has not been reported for the AA10 family. Mutation of the key residues, Trp51 located at subsite - 2 and Phe171 located at subsite +2, in the substrate-binding site of PcAA10A_CD revealed that these residues are substantially involved in broad substrate specificity toward cellulose, xylan, and mannan, albeit with a low effect toward chitin. Furthermore, PcAA10A had a boosting effect on untreated corn hull degradation by P. curdlanolyticus B-6 endo-xylanase Xyn10D and Clostridium thermocellum endo-glucanase Cel9A. These results suggest that PcAA10A is a unique LPMO capable of cleaving and enhancing lignocellulosic biomass degradation, making it a good candidate for biotechnological applications. KEY POINTS: • PcAA10A is a novel modular LPMO family 10 from Paenibacillus curdlanolyticus. • PcAA10A showed broad substrate specificity on β-1,4 glycosidic linkage substrates. • Non-catalytic domains are important for degrading complex polysaccharides. • PcAA10A is a unique LPMO capable of enhancing lignocellulosic biomass degradation.

Effect of wet air oxidation on the composition and biomethanation of water hyacinth

Water hyacinth (Pontederia crassipes) is a potential feedstock for biorefinery due to its rapid growth and phytoremediation properties when cultivated in wastewaters. The effects of wet air oxidation (WAO) and alkaline wet air oxidation (AWAO) on the structure and biomethanation kinetics of water hyacinth were studied. Water hyacinth (50 g/L) was pretreated using WAO and AWAO (0.15 g Na2CO3/g feed), at 170 °C under 0.4 MPa air for 30 min. After WAO and AWAO, the fixed carbon (% w/w) of water hyacinth (25.9 ± 0.8) was reduced to an average of 21.4 ± 1.6. The volatiles (% w/w) in the WAO solid residue were higher (69.0 ± 0.7) than in the AWAO (60.5 ± 1.2) and unpretreated biomass (62.9 ± 0.2), but the soluble COD [mg/g feed] of WAO (153.5 ± 4.1) was half that of AWAO (310.3 ± 4.1). The AWAO biomass showed higher cellulose deconstruction and lignin and extractives removal compared with WAO and unpretreated biomass. The methane production rate [N. mL CH4/g feed day] during the biomethanation of water hyacinth (4.1 ± 0.2) increased 63% after WAO (6.7 ± 1.5) and 117% after AWAO (8.9 ± 0.7). AWAO increased the methane potential [N. mL CH4/g feed] of water hyacinth by 24%, from 153.7 ± 1.9 to 191 ± 4.1. The estimated energy production from the biomethanation of AWAO water hyacinth was 30 times above that of unpretreated biomass. The biomethanation of water hyacinth after AWAO was better than WAO and unpretreated biomass.

Nanostructural Analysis of Enzymatic and Non-enzymatic Brown Rot Fungal Deconstruction of the Lignocellulose Cell Wall†.

Brown rot (BR) decay mechanisms employ carbohydrate-active enzymes (CAZymes) as well as a unique non-enzymatic chelator-mediated Fenton (CMF) chemistry to deconstruct lignocellulosic materials. Unlike white rot fungi, BR fungi lack peroxidases for lignin deconstruction, and also lack some endoglucanase/cellobiohydrolase activities. The role that the CMF mechanism plays in “opening up” the wood cell wall structure in advance of enzymatic action, and any interaction between CMF constituents and the selective CAZyme suite that BRs possess, is still unclear. Expression patterns for CMF redox metabolites and lytic polysaccharide monooxygenase (LPMO–AA9 family) genes showed that some LPMO isozymes were upregulated with genes associated with CMF at early stages of brown rot by Gloeophyllum trabeum. In the structural studies, wood decayed by the G. trabeum was compared to CMF-treated wood, or CMF-treated wood followed by treatment with either the early-upregulated LPMO or a commercial CAZyme cocktail. Structural modification of decayed/treated wood was characterized using small angle neutron scattering. CMF treatment produced neutron scattering patterns similar to that of the BR decay indicating that both systems enlarged the nanopore structure of wood cell walls to permit enzyme access. Enzymatic deconstruction of cellulose or lignin in raw wood samples was not achieved via CAZyme cocktail or LPMO enzyme action alone. CMF treatment resulted in depolymerization of crystalline cellulose as attack progressed from the outer regions of individual crystallites. Multiple pulses of CMF treatment on raw wood showed a progressive increase in the spacing between the cellulose elementary fibrils (EFs), indicating the CMF eroded the matrix outside the EF bundles, leading to less tightly packed EFs. Peracetic acid delignification treatment enhanced subsequent CMF treatment effects, and allowed both enzyme systems to further increase spacing of the EFs. Moreover, even after a single pulse of CMF treatment, both enzymes were apparently able to penetrate the cell wall to further increase EF spacing. The data suggest the potential for the early-upregulated LPMO enzyme to work in association with CMF chemistry, suggesting that G. trabeum may have adopted mechanisms to integrate non-enzymatic and enzymatic chemistries together during early stages of brown rot decay.

Synthetic fungal multifunctional cellulases for enhanced biomass conversion

Synthetic multifunctional enzymes exhibit superior performance to their non-multifunctional enzyme components and exhibit novel cellulose deconstruction mechanisms.

A kinetic study on the hydrolysis of corncob residues to levulinic acid in the FeCl3–NaCl system

Levulinic acid (LA) production from corncob acid hydrolysis residues (CAHR) using FeCl3 as Lewis acid catalyst in green solutions of salt was investigated. The reaction kinetic relationships were determined in the temperature range of 160–180 °C, with FeCl3 concentrations of 0.12–0.36 M, and a reaction time of 0–60 min. The maximum LA concentration of 59.0 mol% (24.5 g/L) was achieved at 170 °C in a 30% NaCl solution containing 0.24 M FeCl3. A pseudo first-order kinetic model was proposed to describe the cellulose deconstruction to LA. The model agreed perfectly with the evolution in the concentrations of the major compounds such as glucose, 5-hydroxymethylfurfural and LA during the CAHR hydrolysis. The kinetic model developed for CAHR was in good agreement with that previously developed for other lignocellulosic systems. Based on our kinetic model and reaction system, the LA yield is increased at the lower end of the temperature range with the higher acid concentrations. The results indicated that the concentrated seawater after desalination could be a green solvent in the biorefinery.

Changes in composition and structure of water hyacinth based on various pretreatment methods

The deconstruction of cellulose, hemicellulose, and lignin has varying effects on lignocellulosic biomass. To understand and evaluate these effects it is important to conduct compositional and structural analyses. In this study, the effect of different pretreatments on the composition and structure of water hyacinth (WH) was investigated. The pretreatment methods investigated were acid, alkali, ionic liquid (IL), and microwave-alkali. The structural analysis was completed before and after the pretreatment using scanning electron microscopy. In addition, the biomass recovery rate was measured to evaluate the composition of the WH biomass. Based on the results, all pretreatment methods effectively disrupted the crystalline structure and enhanced the digestibility of the WH through increasing the cellulose and hemicellulose content and reducing the lignin content. The acid pretreatment resulted in high cellulose digestibility while the microwave-alkali pretreatment destroyed only the lignin structure of the WH. The alkali and IL pretreatments increased the cellulose and hemicellulose content of the WH. The highest recovery rate was obtained via IL pretreatment. The acid, microwave-alkali, and alkali pretreatments had the second, third, and fourth highest recovery rates, respectively. This study showed that the biomass recovery rate, compositional makeup, and structural analysis are important to use WH for bioenergy production.

Correlative Microbially-Assisted Imaging of Cellulose Deconstruction with Electron Microscopy

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Function, distribution, and annotation of characterized cellulases, xylanases, and chitinases from CAZy.

The enzymatic deconstruction of structural polysaccharides, which relies on the production of specific glycoside hydrolases (GHs), is an essential process across environments. Over the past few decades, researchers studying the diversity and evolution of these enzymes have isolated and biochemically characterized thousands of these proteins. The carbohydrate-active enzymes database (CAZy) lists these proteins and provides some metadata. Here, the sequences and metadata of characterized sequences derived from GH families associated with the deconstruction of cellulose, xylan, and chitin were collected and discussed. First, although few polyspecific enzymes are identified, characterized GH families are mostly monospecific. Next, the taxonomic distribution of characterized GH mirrors the distribution of identified sequences in sequenced genomes. This provides a rationale for connecting the identification of GH sequences to specific reactions or lineages. Finally, we tested the annotation of the characterized GHs using HMM scan and the protein families database (Pfam). The vast majority of GHs targeting cellulose, xylan, and chitin can be identified using this publicly accessible approach.

Advanced Cloning Tools for Construction of Designer Cellulosomes.

Cellulose deconstruction is achieved in nature through two main enzymatic paradigms, i.e., free enzymes and enzymatic complexes (called cellulosomes). Gaining insights into the mechanism of action and synergy among the different cellulases is of high interest, notably in the field of renewable energy, and specifically, for the conversion of cellulosic biomass to soluble sugars, en route to biofuels. In this context, designer cellulosomes are artificially assembled, chimaeric protein complexes that are used as a tool to comparatively study cellulose degradation by different enzymatic paradigms, and could also serve to improve cellulose deconstruction. Various molecular biology techniques are employed in order to design and engineer the various components of designer cellulosomes. In this chapter, we describe the cloning processes through which the appropriate modules are selected and assembled at the molecular level.

Heterologous expression of a β-D-glucosidase in Caldicellulosiruptor bescii has a surprisingly modest effect on the activity of the exoproteome and growth on crystalline cellulose.

Members of the genus Caldicellulosiruptor are the most thermophilic cellulolytic bacteria so far described and are capable of efficiently utilizing complex lignocellulosic biomass without conventional pretreatment. Previous studies have shown that accumulation of high concentrations of cellobiose and, to a lesser extent, cellotriose, inhibits cellulase activity both in vivo and in vitro and high concentrations of cellobiose are present in C. bescii fermentations after 90h of incubation. For some cellulolytic microorganisms, β-D-glucosidase is essential for the efficient utilization of cellobiose as a carbon source and is an essential enzyme in commercial preparations for efficient deconstruction of plant biomass. In spite of its ability to grow efficiently on crystalline cellulose, no extracellular β-D-glucosidase or its GH1 catalytic domain could be identified in the C. bescii genome. To investigate whether the addition of a secreted β-D-glucosidase would improve growth and cellulose utilization by C. bescii, we cloned and expressed a thermostable β-D-glucosidase from Acidothermus cellulolyticus (Acel_0133) in C. bescii using the CelA signal sequence for protein export. The effect of this addition was modest, suggesting that β-D-glucosidase is not rate limiting for cellulose deconstruction and utilization by C. bescii.

Organosolv-Water Cosolvent Phase Separation on Cellulose and its Influence on the Physical Deconstruction of Cellulose: A Molecular Dynamics Analysis

Deconstruction of cellulose is crucial for the chemical conversion of lignocellulose into fuel/bioproduct precursors. Recently, a water-organosolv cosolvent system (THF-water) has been shown to both phase-separate on cellulose surfaces and partially deconstruct Avicel (cellulose) in the absence of acid. Here we employ molecular dynamics simulations to determine whether other common water-organosolv cosolvent systems (acetone, ethanol, and γ-valerolactone) exhibit phase separation at cellulose surface and whether this alters a purely physical cellulose dissociation pathway. Despite finding varied degrees of phase-separation of organosolv on cellulose surfaces, physical dissociation is not enhanced. Interestingly, however, the total amount the median water-cellulose contact lifetimes increases for the cosolvent systems in the order of THF > acetone > ethanol > γ-valerolactone. Together our results indicate two points: a purely physical process for deconstruction of cellulose is unlikely for these cosolvents, and in THF-water, unlike γ-valerolactone- (and some concentrations of acetone and ethanol) water cosolvents, a significant fraction of surface water is slowed. This slowing may be of importance in enhancing chemical deconstruction of cellulose, as it permits an increase in potential THF-water-cellulose reactions, even while the amount of water near cellulose is decreased.

Single-molecule study of oxidative enzymatic deconstruction of cellulose

LPMO (lytic polysaccharide monooxygenase) represents a unique paradigm of cellulosic biomass degradation by an oxidative mechanism. Understanding the role of LPMO in deconstructing crystalline cellulose is fundamental to the enzyme’s biological function and will help to specify the use of LPMO in biorefinery applications. Here we show with real-time atomic force microscopy that C1 and C4 oxidizing types of LPMO from Neurospora crassa (NcLPMO9F, NcLPMO9C) bind to nanocrystalline cellulose with high preference for the very same substrate surfaces that are also used by a processive cellulase (Trichoderma reesei CBH I) to move along during hydrolytic cellulose degradation. The bound LPMOs, however, are immobile during their adsorbed residence time ( ~ 1.0 min for NcLPMO9F) on cellulose. Treatment with LPMO resulted in fibrillation of crystalline cellulose and strongly ( ≥ 2-fold) enhanced the cellulase adsorption. It also increased enzyme turnover on the cellulose surface, thus boosting the hydrolytic conversion.

Structural studies of Neurospora crassa LPMO9D and redox partner CDHIIA using neutron crystallography and small-angle scattering

Sensitivity to hydrogen/deuterium and lack of observable radiation damage makes cold neutrons an ideal probe the structural studies of proteins with highly photosensitive groups such as the copper center of lytic polysaccharide monooxygenases (LPMOs) and flavin adenine dinucleotide (FAD) and heme redox cofactors of cellobiose dehydrogenases (CDHs). Here, neutron crystallography and small-angle neutron scattering are used to investigate Neurospora crassa LPMO9D (NcLPMO9D) and CDHIIA (NcCDHIIA), respectively. The presence of LPMO greatly enhances the efficiency of commercial glycoside hydrolase cocktails in the depolymerization of cellulose. LPMOs can receive electrons from CDHs to activate molecular dioxygen for the oxidation of cellulose resulting in chain cleavage and disruption of local crystallinity. Using neutron protein crystallography, the hydrogen/deuterium atoms of NcLPMO9D could be located throughout the structure. At the copper active site, the protonation states of the side chains of His1, His84, His157 and Tyr168, and the orientation of water molecules could be determined. Small-angle neutron scattering measurements provided low resolution models of NcCDHIIA with both the dehydrogenase and cytochrome domains in oxidized states that exhibited elongated conformations. This work demonstrates the suitability of neutron diffraction and scattering for characterizing enzymes critical to oxidative cellulose deconstruction.

Stability and Ligand Promiscuity of Type A Carbohydrate-binding Modules Are Illustrated by the Structure of Spirochaeta thermophila StCBM64C

Deconstruction of cellulose, the most abundant plant cell wall polysaccharide, requires the cooperative activity of a large repertoire of microbial enzymes. Modular cellulases contain non-catalytic type A carbohydrate-binding modules (CBMs) that specifically bind to the crystalline regions of cellulose, thus promoting enzyme efficacy through proximity and targeting effects. Although type A CBMs play a critical role in cellulose recycling, their mechanism of action remains poorly understood. Here we produced a library of recombinant CBMs representative of the known diversity of type A modules. The binding properties of 40 CBMs, in fusion with an N-terminal GFP domain, revealed that type A CBMs possess the ability to recognize different crystalline forms of cellulose and chitin over a wide range of temperatures, pH levels, and ionic strengths. A Spirochaeta thermophila CBM64, in particular, displayed plasticity in its capacity to bind both crystalline and soluble carbohydrates under a wide range of extreme conditions. The structure of S. thermophila StCBM64C revealed an untwisted, flat, carbohydrate-binding interface comprising the side chains of four tryptophan residues in a co-planar linear arrangement. Significantly, two highly conserved asparagine side chains, each one located between two tryptophan residues, are critical to insoluble and soluble glucan recognition but not to bind xyloglucan. Thus, CBM64 compact structure and its extended and versatile ligand interacting platform illustrate how type A CBMs target their appended plant cell wall-degrading enzymes to a diversity of recalcitrant carbohydrates under a wide range of environmental conditions.

Fast purification method of functional LPMOs from Streptomyces ambofaciens by affinity adsorption

A simple purification method by affinity adsorption was developed to obtain functional lytic polysaccharide monooxygenases (LPMOs). The system allows the successful purification to homogeneity of the most characterized bacterial LPMO, CBP21 from Serratia marcescens, and two LPMOs from Streptomyces ambofaciens, which have not been previously characterized. The first of these new LPMOs, named SamLPMO10B is a small enzyme (15 kDa) belonging to family 10 of auxiliary activities (AA10), showing activity on β-chitin. The second LPMO, SamLPMO10C (34.7 kDa), is a bimodular enzyme comprised of an AA10 catalytic module and a carbohydrate binding module of family CBM2. SamLPMO10C shows activity on cellulosic substrates, including agricultural fiber paper pulps. The methodology developed simplifies the purification process to a binding-elution protocol with low-grade polysaccharides including Avicel. The strategy can be a cheap, simple and fast solution for the purification of LPMOs for industrial applications, leaving out periplasmic fractionation from recombinant strains therefore, with reduction of time and costs compared to conventional processes. The activity of SamLPMO10C expands the potential of the high valued LPMOs in lignocellulosic biomass valorization, reaffirming their promising role in cellulose deconstruction.

A bacterial GH6 cellobiohydrolase with a novel modular structure.

Cel6D from Paenibacillus barcinonensis is a modular cellobiohydrolase with a novel molecular architecture among glycosyl hydrolases of family 6. It contains an N-terminal catalytic domain (family 6 of glycosyl hydrolases (GH6)), followed by a fibronectin III-like domain repeat (Fn31,2) and a C-terminal family 3b cellulose-binding domain (CBM3b). The enzyme has been identified and purified showing catalytic activity on cellulosic substrates and cellodextrins, with a marked preference for phosphoric acid swollen cellulose (PASC). Analysis of mode of action of Cel6D shows that it releases cellobiose as the only hydrolysis product from cellulose. Kinetic parameters were determined on PASC showing a K m of 68.73mg/ml and a V max of 1.73U/mg. A series of truncated derivatives of Cel6D have been constructed and characterized. Deletion of CBM3b caused a notable reduction in hydrolytic activity, while deletion of the Fn3 domain abolished activity, as the isolated GH6 domain was not active on any of the substrates tested. Mutant enzymes Cel6D-D146A and Cel6D-D97A were constructed in the residues corresponding to the putative acid catalyst and to the network for the nucleophilic attack. The lack of activity of the mutant enzymes indicates the important role of these residues in catalysis. Analysis of cooperative activity of Cel6D with cellulases from the same producing P. barcinonensis strain reveals high synergistic activity with processive endoglucanase Cel9B on hydrolysis of crystalline substrates. The characterized cellobiohydrolase can be a good contribution for depolymerization of cellulosic substrates and for the deconstruction of native cellulose.