Cloning, expression, and characterization of a thermostable GH7 endoglucanase from Myceliophthora thermophila capable of high-consistency enzymatic liquefaction

Heterologous Expression of Thermostable Endoglucanases from Rasamsonia emersonii: A Paradigm Shift in Biomass Hydrolysis

In this study, two thermostable endoglucanases (Rem_GH5EG and Rem_GH7EG) from Rasamsonia emersonii were heterologously expressed in Pichia pastoris and characterized to evaluate their potential for industrial biomass saccharification. Rem_GH5EG demonstrated markedly superior catalytic efficiency toward barley β-glucan (kcat/Km = 6.3 × 10-3/mg mL/min), while Rem_GH7EG exhibited a preference for carboxymethyl cellulose (kcat/Km = 1.17 × 10-3/mg mL/min). Notably, Rem_GH5EG showed optimal activity at 90 °C with a half-life (t1/2) of 2 h, whereas Rem_GH7EG was active at 70 °C with a half-life (t1/2) of 1 h, highlighting its suitability for high-temperature hydrolysis processes. Moreover, pre-conditioning of steam and acid pretreated unwashed rice straw slurry with Rem_GH5EG at 90 °C effectively reduced viscosity-related mass transfer limitations, thereby enhancing the hydrolytic efficiency of benchmark cellulase. These findings underscore the industrial relevance of Rem_GH5EG as the more promising candidate for developing efficient enzyme cocktails for biomass saccharification.

Exploring the synergy between fungal CE15 glucuronoyl esterases and xylanases for lignocellulose saccharification

BACKGROUND

Lignin-carbohydrate complexes in lignocellulosic biomass act as a barrier to its biodegradation and biotechnological exploitation. Enzymatic dissociation between lignin and hemicellulose is a key process that allows the efficient bioconversion of both polymers. Glucuronoyl esterases of the Carbohydrate Esterase 15 family target the ester linkages between the glucuronic acid of xylan and lignin moieties, assisting enzymatic biodegradation of lignocellulose.

RESULTS

In this study, two CE15 glucuronoyl esterases from the white-rot fungi Artolenzites elegans and Trametes ljubarskyi were heterologously expressed in Pichia pastoris and biochemically characterized on the model substrate D-glucuronic acid ester with cinnamyl alcohol and a variety of pretreated lignocellulosic biomasses. The pretreatment method was shown to be a determining factor in revealing both the activity of the esterases on lignocellulose and their synergistic relationships with other hemicellulases. AeGE15 and TlGE15 demonstrated activity on pretreated biomass with high hemicellulose and lignin content, increasing saccharification by 57 ± 1 μM and 61 ± 3 μM of xylose equivalents, respectively. Furthermore, the synergy between these CE15 esterases and three xylanases from distinct glycoside hydrolase families (GH10, GH11 and GH30) was investigated on pretreated lignocellulosic samples, highlighting beneficial enzymatic interplays. Pretreated birchwood degradation by AnXyn11 was increased from 6% to approximately 10% by the esterases, based on xylose equivalents of unsubstituted xylooligomers. The GEs also promoted the glucuronoxylanase specificity of TtXyn30A, leading up to three-times higher release in aldouronic acids. Finally, a synergistic effect between AeGE15 and TmXyn10 was observed on pretreated corn bran, increasing xylose and xylotriose release by 27 ± 8% and 55 ± 15%, respectively.

CONCLUSIONS

Both CE15 esterases promoted biomass saccharification by the xylanases, while there was a prominent effect on the GH30 glucuronoxylanase regarding the release of aldouronic acids. Overall, this study shed some light on the role of CE15 glucuronoyl esterases in the enzymatic biodegradation of plant biomass, particularly its (arabino)glucuronoxylan component, during cooperative activity with xylanases.

Special Issue: "Microbial Enzymes for Biotechnological Applications"

Microbial biocatalysts are at the forefront of modern biotechnology, offering sustainable solutions to some of the world's most pressing environmental and industrial challenges [...].

Characterization of a novel acidophilic, ethanol tolerant and halophilic GH12 β-1,4-endoglucanase from Trichoderma asperellum ND-1 and its synergistic hydrolysis of lignocellulosic biomass

A novel acidophilic GH5 β-1,4-endoglucanase (TaCel12) from Trichoderma asperellum ND-1 was efficiently expressed in Pichia pastoris (a 1.5-fold increase). Deglycosylated TaCel12 migrated as a single band (26.5 kDa) in SDS-PAGE. TaCel12 was acidophilic with a pH optimum of 4.0 and displayed great pH stability (>80 % activity over pH 3.0-5.0). TaCel12 exhibited considerable activity towards sodium carboxymethyl cellulose and sodium alginate with Vmax values of 197.97 μmol/min/mg and 119.06 μmol/min/mg, respectively. Moreover, TaCel12 maintained >80 % activity in the presence of 20 % ethanol and 4.28 M NaCl. Additionally, Mn2+, Pb2+ and Cu2+ negatively affected TaCel12 activity, while the presence of 5 mM Co2+ significantly increased the enzyme activity. Analysis of action mode revealed that TaCel12 required at least four glucose (cellotetraose) residues for hydrolysis to yield cellobiose and cellotriose. Site-directed mutagenesis results suggested that Glu133 and Glu217 of TaCel12 are crucial catalytic residues, with Asp116 displaying an auxiliary function. Production of soluble sugars from lignocellulose is a crucial step in bioethanol development, and it is noteworthy that TaCel12 could synergistically yield fermentable sugars from corn stover and bagasse, respectively. Thus TaCel12 with excellent properties will be considered a potential biocatalyst for applications in various industries, especially for lignocellulosic biomass conversion.

Modulation of the catalytic activity and thermostability of a thermostable GH7 endoglucanase by engineering the key loop B3

The loop B3 of glycoside hydrolase family 7 (GH7) endoglucanases is confined into long and short types. TtCel7 is a thermophilic GH7 endoglucanase from Thermothelomyces thermophilus ATCC 42464 with a long loop B3. TtCel7 was distinct for the excellent thermostability (>30 % residual activity after 1-h incubation at 90 °C). The catalytic efficiency was reduced by removing the disulfide bond in loop B3 (C220A) and truncated the loop B3 (B3cut). However, B3cut exhibited improved thermostability, the remaining enzyme activity increased by 39 %-171 % compared toTtCel7 when treated at 70-90 °C for 1-h. Based on the analysis of molecular dynamics simulation, both loops B1 and A3 of B3cut swing toward the catalytic center, which contributed to the reduced cleft-space and increased structure-rigidity. Conversely, the deletion of disulfide bond resulted in a reduction of structural rigidity in C220A. Through structure-directed enzyme modulation, this study has identified two structural elements that are related to the catalysis and thermostability of TtCel7. The loop B3 of TtCel7 possibly stretches the catalytic pocket, thereby increases the openness of the catalytic tunnel and enhancing flexibility for efficient catalysis. Additionally, the disulfide bond within loop B3 serves to enhance structural stability and maintain a heightened level of activity.

Production and Characterization of Cellulose Nanocrystals from Eucalyptus Dissolving Pulp Using Endoglucanases from Myceliophthora thermophila

Endoglucanase (EG) is a key enzyme during enzymatic preparation of cellulose nanocrystals (CNCs). Myceliophthora thermophila is a thermophilic fungus that has thermal properties and a high secretion of endoglucanases (EGs), and could serve as potential sources of EGs for the preparation of CNCs. In this work, four different GH families (GH5, GH7, GH12, and GH45) of EGs from M. thermophila were expressed and purified, and their enzymatic characteristics and feasibility of application in CNC preparation were investigated. It was shown that the MtEG5A from M. thermophila has good potential in the enzymatic preparation of CNCs using eucalyptus dissolving pulp as feedstock. It was also observed that there was a synergistic effect between the MtEG5A and other MtEGs in the preparation of CNCs, which improved the yield and properties of CNCs obtained by enzymatic hydrolysis. This study provides a reference for understanding the enzymatic characteristics of different families of EGs from M. thermophile and their potential application in nanocellulose production.

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

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

TtCel7A: A Native Thermophilic Bifunctional Cellulose/Xylanase Exogluclanase from the Thermophilic Biomass-Degrading Fungus Thielavia terrestris Co3Bag1, and Its Application in Enzymatic Hydrolysis of Agroindustrial Derivatives

The biomass-degrading thermophilic ascomycete fungus Thielavia terrestris Co3Bag1 produces TtCel7A, a native bifunctional cellulase/xylanase GH7 family. The purified TtCel7A, with an estimated molecular weight of 71 kDa, was biochemically characterized. TtCel7A displayed an optimal pH of 5.5 for both activities and an optimal temperature of 60 and 50 °C for cellulolytic and xylanolytic activities, respectively. The half-lives determined for cellulase activity were 140, 106, and 41 min at 50, 60, and 70 °C, respectively, whereas the half-lives observed for xylanase activity were 24, 10, and 1.4 h at 50, 60, and 70 °C, respectively. The K_M and V_max values were 3.12 mg/mL and 50 U/mg for cellulase activity and 0.17 mg/mL and 42.75 U/mg for xylanase activity. Circular dichroism analysis suggests changes in the secondary structure of TtCel7A in the presence of CMC as the substrate, whereas no modifications were observed with beechwood xylan. TtCel7A displayed the excellent capability to hydrolyze CMC, beechwood xylan, and complex substrates such as oat bran, wheat bran, and sugarcane bagasse, with glucose and cellobiose being the main products released; also, slightly less endo cellulase and xylanase activities were observed. Thus, suggesting TtCel7A has an exo- and endomode of action. Based on the characteristics of the enzyme, it might be considered a good candidate for industrial applications.

Simultaneous manipulation of multiple genes within a same regulatory stage for iterative evolution of Trichoderma reesei

Background

While there is growing interest in developing non-canonical filamentous fungi as hosts for producing secretory proteins, genetic engineering of filamentous fungi for improved expression often relies heavily on the understanding of regulatory mechanisms.

Results

In this study, using the cellulase-producing filamentous fungus Trichoderma reesei as a model system, we designed a semi-rational strategy by arbitrarily dividing the regulation of cellulase production into three main stages-transcription, secretion, and cell metabolism. Selected regulatory or functional genes that had been experimentally verified or predicted to enhance cellulase production were overexpressed using strong inducible or constitutive promoters, while those that would inhibit cellulase production were repressed via RNAi-mediated gene silencing. A T. reesei strain expressing the surface-displayed DsRed fluorescent protein was used as the recipient strain. After three consecutive rounds of engineering, the cellulase activity increased to up to 4.35-fold and the protein concentration increased to up to 2.97-fold in the genetically modified strain.

Conclusions

We demonstrated that, as a proof-of-concept, selected regulatory or functional genes within an arbitrarily defined stage could be pooled to stimulate secretory cellulase production, and moreover, this method could be iteratively used for further improvement. This method is semi-rational and can essentially be used in filamentous fungi with little regulatory information.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02122-0.

Expression, characterization, and activity optimization of a novel cellulase from the thermophilic bacteria Cohnella sp. A01

Cellulases are hydrolytic enzymes with wide scientific and industrial applications. We described a novel cellulase, CelC307, from the thermophilic indigenous Cohnella sp. A01. The 3-D structure of the CelC307 was predicted by comparative modeling. Docking of CelC307 with specific inhibitors and molecular dynamic (MD) simulation revealed that these ligands bound in a non-competitive manner. The CelC307 protein was purified and characterized after recombinant expression in Escherichia coli (E. coli) BL21. Using CMC 1% as the substrate, the thermodynamic values were determined as K_m 0.46 mM, k_cat 104.30 × 10^-3 (S^-1), and k_cat/K_m 226.73 (M^-1 S^-1). The CelC307 was optimally active at 40 °C and pH 7.0. The culture condition was optimized for improved CelC307 expression using Plackett-Burman and Box-Behnken design as follows: temperature 20 °C, pH 7.5, and inoculation concentration with an OD₆₀₀ = 1. The endoglucanase activity was positively modulated in the presence of Na⁺, Li⁺, Ca²⁺, 2-mercaptoethanol (2-ME), and glycerol. The thermodynamic parameters calculated for CelC307 confirmed its inherent thermostability. The characterized CelC307 may be a suitable candidate for various biotechnological applications.

Lytic polysaccharide monooxygenases as powerful tools in enzymatically assisted preparation of nano-scaled cellulose from lignocellulose: A review

Nanocellulose, either in the form of fibers or crystals, constitutes a renewable, biobased, biocompatible material with advantageous mechanical properties that can be isolated from lignocellulosic biomass. Enzyme-assisted isolation of nanocellulose is an attractive, environmentally friendly approach that leads to products of higher quality compared to their chemically prepared counterparts. Lytic polysaccharide monooxygenases (LPMOs) are enzymes that oxidatively cleave the β-1,4-glycosidic bond of polysaccharides upon activation of O₂ or H₂O₂ and presence of an electron donor. Their use for treatment of cellulose fibers towards the preparation of nano-scaled cellulose is related to the ability of LPMOs to create nicking points on the fiber surface, thus facilitating fiber disruption and separation. The aim of this review is to describe the mode of action of LPMOs on cellulose fibers towards the isolation of nanostructures, thus highlighting their great potential for the production of nanocellulose as a novel value added product from lignocellulose.

Heterologous expression and characterization of glycoside hydrolase with its potential applications in hyperthermic environment

With the progressive focus on renewable energy via biofuels production from lignocellulosic biomass, cellulases are the key enzymes that play a fundamental role in this regard. This study aims to unravel the characteristics of Thermotoga maritima MSB8 (Tma) (a hyperthermophile from hot springs) thermostable glycoside hydrolase enzyme. Here, a glycoside hydrolase gene of Thermotoga maritima (Tma) was heterologously expressed and characterized. The gene was placed in the pQE-30 expression vector under the T5 promotor, and the construct pQE-30-Gh was then successfully integrated into Escherichia coli BL21 (DH5α) genome by transformation. Sequence of the glycoside hydrolase contained an open reading frame of 2.124 kbp, encoded a polypeptide of 721 amino acid residues. The molecular weight of the recombinant protein estimated was 79 kDa. The glycoside hydrolase was purified by Ni⁺²-NTA affinity chromatography and its enzymatic activity was investigated. The recombinant enzyme is highly stable within an extreme pH range (2.0–7.0) and highly thermostable at 80 °C for 72 h indicating its viability in hyperthermic environment and acidic nature. Moreover, the Ca²⁺ and Mn²⁺ introduction stimulated the residual activity of recombinant enzyme. Conclusively, the thermostable glycoside hydrolase possesses potential to be exploited for industrial applications at hyperthermic environment.

Novel thermo-alkali-stable cellulase-producing Serratia sp. AXJ-M cooperates with Arthrobacter sp. AXJ-M1 to improve degradation of cellulose in papermaking black liquor

There is an urgent requirement to treat cellulose present in papermaking black liquor since it induces severe economic wastes and causes environmental pollution. We characterized cellulase activity at different temperatures and pH to seek thermo-alkali-stable cellulase-producing bacteria, a natural consortium of Serratia sp. AXJ-M and Arthrobacter sp. AXJ-M1 was used to improve the degradation of cellulose. Notably, the enzyme activities and the degradation rate of cellulose were increased by 30%-70% and 30% after co-culture, respectively. In addition, the addition of cosubstrates increased the degradation rate of cellulose beyond 30%. The thermo-alkali-stable endoglucanase (bcsZ) gene was derived from the strain AXJ-M and was cloned and expressed. The purified bcsZ displayed the maximum activity at 70 °C and pH 9. Mn²⁺, Ca²⁺, Mg²⁺ and Tween-20 had beneficial effects on the enzyme activity. Structurally, bcsZ potentially catalyzed the degradation of cellulose. The co-culture with ligninolytic activities significantly decreased target the parameters (cellulose 45% and COD 95%) while using the immobilized fluidized bed reactors (FBRs). Finally, toxicological tests and antioxidant enzyme activities indicated that the co-culture had a detoxifying effect on black liquor. Our study showed that Serratia sp. AXJ-M acts synergistically with Arthrobacter sp. AXJ-M1 may be potentially useful for bioremediation for black liquor.

Improvement of catalytic performance of endoglucanase CgEndo from Colletotrichum graminicola by site-directed mutagenesis

In order to improve the catalytic efficiency of cellulase for more effective utilization of lignocellulose, a novel endoglucanase (CgEndo) from Colletotrichum graminicola was expressed by Pichia pastoris X33 and modified by site-directed mutagenesis. Two mutants, Y63S and N20D/S113T, with 62.31% and 57.14% increased enzyme activities were obtained, respectively. On this basis, their biochemical properties, kinetic parameters, structural information as well as the application in biomass degradation were investigated and compared with the wild-type CgEngo. The results indicated that the mutation Y63S and N20D/S113T resulted in an improvement of proximity between enzyme and substrate through conformational changes of the catalytic region, which might contribute to the higher enzyme activities and catalysis efficiency (K_cat/K_m) of Y63S and N20D/S113T. These findings laid important foundation for the further engineering of this endoglucanase and practical application in efficient degradation of cellulosic biomass in nature.

Conversion of organosolv pretreated hardwood biomass into 5-hydroxymethylfurfural (HMF) by combining enzymatic hydrolysis and isomerization with homogeneous catalysis

BACKGROUND

Over the last few years, valorization of lignocellulosic biomass has been expanded beyond the production of second-generation biofuels to the synthesis of numerous platform chemicals to be used instead of their fossil-based counterparts. One such well-researched example is 5-hydroxymethylfurfural (HMF), which is preferably produced by the dehydration of fructose. Fructose is obtained by the isomerization of glucose, which in turn is derived by the hydrolysis of cellulose. However, to avoid harsh reaction conditions with high environmental impact, an isomerization step towards fructose is necessary, as fructose can be directly dehydrated to HMF under mild conditions. This work presents an optimized process to produce fructose from beechwood biomass hydrolysate and subsequently convert it to HMF by employing homogeneous catalysis.

RESULTS

The optimal saccharification conditions were identified at 10% wt. solids loading and 15 mg enzyme/g_solids, as determined from preliminary trials on pure cellulose (Avicel® PH-101). Furthermore, since high rate glucose isomerization to fructose requires the addition of sodium tetraborate, the optimum borate to glucose molar ratio was determined to 0.28 and was used in all experiments. Among 20 beechwood solid pulps obtained from different organosolv pretreatment conditions tested, the highest fructose production was obtained with acetone (160 °C, 120 min), reaching 56.8 g/100 g pretreated biomass. A scale-up hydrolysis in high solids (25% wt.) was then conducted. The hydrolysate was subjected to isomerization eventually leading to a high-fructose solution (104.5 g/L). Dehydration of fructose to HMF was tested with 5 different catalysts (HCl, H₃PO₄, formic acid, maleic acid and H-mordenite). Formic acid was found to be the best one displaying 79.9% sugars conversion with an HMF yield and selectivity of 44.6% and 55.8%, respectively.

CONCLUSIONS

Overall, this work shows the feasibility of coupling bio- and chemo-catalytic processes to produce HMF from lignocellulose in an environmentally friendly manner. Further work for the deployment of biocatalysts for the oxidation of HMF to its derivatives could pave the way for the emergence of an integrated process to effectively produce biobased monomers from lignocellulose.

Cello-oligosaccharides production from lignocellulosic biomass and their emerging prebiotic applications

Cello-oligosaccharides (COS) are linear oligosaccharides composed of β-1,4-linked glucopyranose units. They comprise a group of important new oligosaccharides of significant interest and potential applications in the pharmaceutical, food, chemical, and feed industries, currently emerging as potential prebiotic compounds. COS from lignocellulosic biomass, specifically the agro-industrial residues and by-products of the forestry industry, constitute a new attractive process that imposes the sustainable use of biomass resources. Two main strategies have been used for the production of COS: acid-based and enzyme-based cellulose hydrolysis. The latter has been considered more attractive due to the use of milder reaction conditions and less production of monomers. This review summarizes that although COS is emerging as a potential prebiotic with also other potential applications, there is a lack of information regarding the large-scale production, which could be associated with the recalcitrant nature of cellulose compared to other polysaccharides, which hinders the hydrolysis of its dense network.

High efficient degradation of glucan/glucomannan to cello-/mannan-oligosaccharide by endoglucanase via tetrasaccharide as intermediate

Here, we report an efficient endoglucanase from Aureobasidium pullulans (termed ApCel5A) was expressed in Pichia pastoris. ApCel5A shows two different enzyme activities of endoglucanase (1270 U/mg) and mannanase (31.2 U/mg). Through engineering the signal peptide and fed-batch fermentation, the enzyme activity of endoglucanase was improved to 6.63-folds, totally. Its efficient synergism with Celluclast 1.5 L, excellent tolerance to low pH (2.5), cholate and protease suggests potential application in bioresources, food and feed industries. Site-directed mutagenesis experiments present that ApCel5A residues Glu²⁴⁵ and Glu³⁵⁸ are key catalytic sites, while Asp¹¹⁸, Asp¹²², Asp¹⁹⁸ and Asp³¹⁴ play an auxiliary role. More importantly, ApCel5A display high degradation efficiency of glucan and glucomannan substrates by using tetrasaccharide contained reducing end of glucose residue as an intermediate. This study elucidated the effective methods to improve an endoglucanase expression and detailed catalytic mechanism for degradation of various substrates, which provides a new insight for endoglucanase application.

Valorization of outer tunic of the marine filter feeder Ciona intestinalis towards the production of second-generation biofuel and prebiotic oligosaccharides

BACKGROUND

One of the sustainable development goals focuses on the biomass-based production as a replacement for fossil-based commodities. A novel feedstock with vast potentials is tunicate biomass, which can be pretreated and fermented in a similar way to lignocellulose. Ciona intestinalis is a marine filter feeder that is cultivated to produce fish feed. While the inner tissue body is used for feed production, the surrounding tunic remains as a cellulose-rich by-product, which can be further separated into outer and inner tunic. Ethanol production from organosolv-pretreated whole-tunic biomass was recently validated. The aim of the present study was to evaluate the potential of organosolv pretreated outer-tunic biomass for the production of biofuels and cellobiose that is a disaccharide with prebiotic potential.

RESULTS

As a result, 41.4 g/L of ethanol by Saccharomyces cerevisiae, corresponding to a 90.2% theoretical yield, was achieved under the optimal conditions when the tunicate biomass was pretreated at 195 °C for 60 min at a liquid-to-solid ratio of 50. In addition, cellobiose production by enzymatic hydrolysis of the pretreated tunicate biomass was demonstrated with a maximum conversion yield of 49.7 wt. %.

CONCLUSIONS

The utilisation of tunicate biomass offers an eco-friendly and sustainable alternative for value-added biofuels and chemicals. The cultivation of tunicate biomass in shallow coastal sea improves the quality of the water and ensures sustainable production of fish feed. Moreover, there is no competition for arable land, which leaves the latter available for food and feed production.

Heterologous expression and biochemical characterization of a thermostable endo-β-1,4-glucanase from Colletotrichum orchidophilum

To develop new cellulases for efficient utilization of the lignocellulose, an endoglucanase (CoCel5A) gene from Colletotrichum orchidophilum was synthesized and a recombinant Pichia pastoris GS115/pPIC9K/cocel5A was constructed for secretory expression of CoCel5A. After purification, the protein CoCel5A was biochemically characterized. The endoglucanase CoCel5A exhibited the optimal activity at 55-75 °C and high thermostability (about 85% residual activity) at the temperature of 55 °C after incubation for 3 h. The highest activity of CoCel5A was detected when 100 mM citric acid buffer (pH 4.0-5.0) was used and excellent pH stability (up to 95% residual activity) was observed after incubation in 100 mM citric acid buffer (pH 3.0-6.0) at 4 °C for 24 h. Carboxymethyl cellulose sodium salt (n = approx. 500) (CMC) and β-D-glucan were the best substrates for CoCel5A among the tested substrates. The kinetic parameters V_max, K_m, and K_cat/K_m values against CMC were 290.70 U/mg, 2.65 mg/mL, and 75.67 mL/mg/s, respectively; and 228.31 U/mg, 2.06 mg/mL, and 76.45 mL/mg/s against β-D-glucan, respectively, suggesting that CoCel5A has high affinity and catalytic efficiency. These properties supported the potential application of CoCel5A in biotechnological and environmental fields.

Novel Routes in Transformation of Lignocellulosic Biomass to Furan Platform Chemicals: From Pretreatment to Enzyme Catalysis

The constant depletion of fossil fuels along with the increasing need for novel materials, necessitate the development of alternative routes for polymer synthesis. Lignocellulosic biomass, the most abundant carbon source on the planet, can serve as a renewable starting material for the design of environmentally-friendly processes for the synthesis of polyesters, polyamides and other polymers with significant value. The present review provides an overview of the main processes that have been reported throughout the literature for the production of bio-based monomers from lignocellulose, focusing on physicochemical procedures and biocatalysis. An extensive description of all different stages for the production of furans is presented, starting from physicochemical pretreatment of biomass and biocatalytic decomposition to monomeric sugars, coupled with isomerization by enzymes prior to chemical dehydration by acid Lewis catalysts. A summary of all biotransformations of furans carried out by enzymes is also described, focusing on galactose, glyoxal and aryl-alcohol oxidases, monooxygenases and transaminases for the production of oxidized derivatives and amines. The increased interest in these products in polymer chemistry can lead to a redirection of biomass valorization from second generation biofuels to chemical synthesis, by creating novel pathways to produce bio-based polymers.

A Thermostable Aspergillus fumigatus GH7 Endoglucanase Over-Expressed in Pichia pastoris Stimulates Lignocellulosic Biomass Hydrolysis

In the context of avoiding the use of non-renewable energy sources, employing lignocellulosic biomass for ethanol production remains a challenge. Cellulases play an important role in this scenario: they are some of the most important industrial enzymes that can hydrolyze lignocellulose. This study aims to improve on the characterization of a thermostable Aspergillus fumigatus endo-1,4-β-glucanase GH7 (Af-EGL7). To this end, Af-EGL7 was successfully expressed in Pichia pastoris X-33. The kinetic parameters K_m and V_max were estimated and suggested a robust enzyme. The recombinant protein was highly stable within an extreme pH range (3.0-8.0) and was highly thermostable at 55 °C for 72 h. Low Cu²⁺ concentrations (0.1-1.0 mM) stimulated Af-EGL7 activity up to 117%. Af-EGL7 was tolerant to inhibition by products, such as glucose and cellobiose. Glucose at 50 mM did not inhibit Af-EGL7 activity, whereas 50 mM cellobiose inhibited Af-EGL7 activity by just 35%. Additionally, the Celluclast^® 1.5L cocktail supplemented with Af-EGL7 provided improved hydrolysis of sugarcane bagasse "in natura", sugarcane exploded bagasse (SEB), corncob, rice straw, and bean straw. In conclusion, the novel characterization of Af-EGL7 conducted in this study highlights the extraordinary properties that make Af-EGL7 a promising candidate for industrial applications.

Optimization of cell culture and cell disruption processes to enhance the production of thermophilic cellulase FnCel5A in E.coli using response surface methodology

FnCel5A from Fervidobacterium nodosum is one of the most thermostable endoglucanases that have phenomenal characteristics, such as high activity, pH stability, and multi-specificity towards various substrates. However, large-scale thermophilic enzyme production is still a challenge. Herein, we focus on an optimization approach based on response surface methodology to improve the production of this enzyme. First, a Box-Behnken design was used to examine physiochemical parameters such as induction temperatures, isopropylβ-D-1-thiogalactopyranoside concentrations and induction times on the heterogeneous expression of FnCel5A gene in E. coli. The best culture was collected after adding 0.56 mM IPTG and incubating it for 29.5 h at 24°C. The highest enzymatic activity observed was 3.31 IU/mL. Second, an economical "thermolysis" cell lysis method for the liberation of the enzymes was also optimized using Box-Behnken design. The optimal levels of the variables were temperature 77°C, pH 7.71, and incubation time of 20 min, which gave about 74.3% higher activity than the well-established bead-milling cell disruption method. The maximum productivity of FnCel5A achieved (5772 IU/L) illustrated that its production increased significantly after combining both optimal models. This strategy can be scaled-up readily for overproduction of FnCel5A from recombinant E.coli to facilitate its usage in biomass energy production.

A novel fungal GH30 xylanase with xylobiohydrolase auxiliary activity

BACKGROUND

The main representatives of hemicellulose are xylans, usually decorated β-1,4-linked d-xylose polymers, which are hydrolyzed by xylanases. The efficient utilization and complete hydrolysis of xylans necessitate the understanding of the mode of action of xylan degrading enzymes. The glycoside hydrolase family 30 (GH30) xylanases comprise a less studied group of such enzymes, and differences regarding the substrate recognition have been reported between fungal and bacterial GH30 xylanases. Besides their role in the utilization of lignocellulosic biomass for bioenergy, such enzymes could be used for the tailored production of prebiotic xylooligosaccharides (XOS) due to their substrate specificity.

RESULTS

The expression of a putative GH30_7 xylanase from the fungus Thermothelomyces thermophila (synonyms Myceliophthora thermophila, Sporotrichum thermophile) in Pichia pastoris resulted in the production and isolation of a novel xylanase with unique catalytic properties. The novel enzyme designated TtXyn30A, exhibited an endo- mode of action similar to that of bacterial GH30 xylanases that require 4-O-methyl-d-glucuronic acid (MeGlcA) decorations, in contrast to most characterized fungal ones. However, TtXyn30A also exhibited an exo-acting catalytic behavior by releasing the disaccharide xylobiose from the non-reducing end of XOS. The hydrolysis products from beechwood glucuronoxylan were MeGlcA substituted XOS, and xylobiose. The major uronic XOS (UXOS) were the aldotriuronic and aldotetrauronic acid after longer incubation indicating the ability of TtXyn30A to cleave linear parts of xylan and UXOS as well.

CONCLUSIONS

Hereby, we reported the heterologous production and biochemical characterization of a novel fungal GH30 xylanase exhibiting endo- and exo-xylanase activity. To date, considering its novel catalytic properties, TtXyn30A shows differences with most characterized fungal and bacterial GH30 xylanases. The discovered xylobiohydrolase mode of action offers new insights into fungal enzymatic systems that are employed for the utilization of lignocellulosic biomass. The recombinant xylanase could be used for the production of X2 and UXOS from glucuronoxylan, which in turn would be utilized as prebiotics carrying manifold health benefits.

Valorization of waste forest biomass toward the production of cello-oligosaccharides with potential prebiotic activity by utilizing customized enzyme cocktails

BACKGROUND

Production of value-added materials from lignocellulosic biomass residues is an emerging sector that has attracted much attention as it offers numerous benefits from an environmental and economical point of view. Non-digestible oligosaccharides represent a group of carbohydrates that are resistant to gastrointestinal digestion, and therefore, they are considered as potential prebiotic candidates. Such oligosaccharides can derive from the biomass cellulose fraction through a controlled enzymatic hydrolysis that eliminates the yield of monomers.

RESULTS

In the present study, hydrolysis of organosolv-pretreated forest residues (birch and spruce) was tested in the presence of four cellulases (EG5, CBH7, CBH6, EG7) and one accessory enzyme (LPMO). The optimal enzyme combinations were comprised of 20% EG5, 43% CBH7, 22% TtLPMO, 10% PaCbh6a and 5% EG7 in the case of birch and 35% EG5, 45% CBH7, 10% TtLPMO, 10% PaCbh6a and 5% EG7 in the case of spruce, leading to 22.3% and 19.1 wt% cellulose conversion into cellobiose, respectively. Enzymatic hydrolysis was applied on scale-up reactions, and the produced oligosaccharides (consisted of > 90% cellobiose) were recovered and separated from glucose through nanofiltration at optimized temperature (50 °C) and pressure (10 bar) conditions, yielding a final product with cellobiose-to-glucose ratio of 21.1 (birch) and 20.2 (spruce). Cellobiose-rich hydrolysates were tested as fermentative substrates for different lactic acid bacteria. It was shown that they can efficiently stimulate the growth of two Lactobacilli strains.

CONCLUSIONS

Controlled enzymatic hydrolysis with processive cellulases, combined with product recovery and purification, as well as enzyme recycling can potentially support the sustainable production of food-grade oligosaccharides from forest biomass.

Side-by-side biochemical comparison of two lytic polysaccharide monooxygenases from the white-rot fungus Heterobasidion irregulare on their activity against crystalline cellulose and glucomannan

Our comparative studies reveal that the two lytic polysaccharide monooxygenases HiLPMO9B and HiLPMO9I from the white-rot conifer pathogen Heterobasidion irregulare display clear difference with respect to their activity against crystalline cellulose and glucomannan. HiLPMO9I produced very little soluble sugar on bacterial microcrystalline cellulose (BMCC). In contrast, HiLPMO9B was much more active against BMCC and even released more soluble sugar than the H. irregulare cellobiohydrolase I, HiCel7A. Furthermore, HiLPMO9B was shown to cooperate with and stimulate the activity of HiCel7A, both when the BMCC was first pretreated with HiLPMO9B, as well as when HiLPMO9B and HiCel7A were added together. No such stimulation was shown by HiLPMO9I. On the other hand, HiLPMO9I was shown to degrade glucomannan, using a C4-oxidizing mechanism, whereas no oxidative cleavage activity of glucomannan was detected for HiLPMO9B. Structural modeling and comparison with other glucomannan-active LPMOs suggest that conserved sugar-interacting residues on the L2, L3 and LC loops may be essential for glucomannan binding, where 4 out of 7 residues are shared by HiLPMO9I, but only one is found in HiLPMO9B. The difference shown between these two H. irregulare LPMOs may reflect distinct biological roles of these enzymes within deconstruction of different plant cell wall polysaccharides during fungal colonization of softwood.

Insights into the Synergistic Biodegradation of Waste Papers Using a Combination of Thermostable Endoglucanase and Cellobiohydrolase from Chaetomium thermophilum

Enzymatic hydrolysis is considered an efficient and environmental strategy for the degradation of organic waste materials. Compared to mesophilic cellulases, thermostable cellulases with considerable activity are more advantageous in waste paper hydrolysis, particularly in terms of their participation in synergistic action. In this study, the synergistic effect of two different types of thermostable Chaetomium thermophilum cellulases, the endoglucanase CTendo45 and the cellobiohydrolase CtCel6, on five common kinds of waste papers was investigated. CtCel6 significantly enhanced the bioconversion process, and CTendo45 synergistically increased the degradation, with a maximum degree of synergistic effect of 1.67 when the mass ratio of CTendo45/CtCel6 was 5:3. The synergistic degradation products of each paper material were also determined. Additionally, the activities of CTendo45 and CtCel6 were found to be insensitive to various metals at 2 mM and 10 mM ion concentrations. This study gives an initial insight into a satisfactory synergistic effect of C. thermophilum thermostable cellulases for the hydrolysis of different paper materials, which provides a potential combination of enzymes for industrial applications, including environmentally friendly waste management and cellulosic ethanol production.

Cellulases from Thermophiles Found by Metagenomics

Cellulases are a heterogeneous group of enzymes that synergistically catalyze the hydrolysis of cellulose, the major component of plant biomass. Such reaction has biotechnological applications in a broad spectrum of industries, where they can provide a more sustainable model of production. As a prerequisite for their implementation, these enzymes need to be able to operate in the conditions the industrial process requires. Thus, cellulases retrieved from extremophiles, and more specifically those of thermophiles, are likely to be more appropriate for industrial needs in which high temperatures are involved. Metagenomics, the study of genes and gene products from the whole community genomic DNA present in an environmental sample, is a powerful tool for bioprospecting in search of novel enzymes. In this review, we describe the cellulolytic systems, we summarize their biotechnological applications, and we discuss the strategies adopted in the field of metagenomics for the discovery of new cellulases, focusing on those of thermophilic microorganisms.

Fine-Tuned Enzymatic Hydrolysis of Organosolv Pretreated Forest Materials for the Efficient Production of Cellobiose

Non-digestible oligosaccharides (NDOs) are likely prebiotic candidates that have been related to the prevention of intestinal infections and other disorders for both humans and animals. Lignocellulosic biomass is the largest carbon source in the biosphere, therefore cello-oligosacharides (COS), especially cellobiose, are potentially the most widely available choice of NDOs. Production of COS and cellobiose with enzymes offers numerous benefits over acid-catalyzed processes, as it is milder, environmentally friendly and produces fewer by-products. Cellobiohydrolases (CBHs) and a class of endoglucanases (EGs), namely processive EGs, are key enzymes for the production of COS, as they have higher preference toward glycosidic bonds near the end of cellulose chains and are able to release soluble products. In this work, we describe the heterologous expression and characterization of two CBHs from the filamentous fungus Thermothelomyces thermophila, as well as their synergism with proccessive EGs for cellobiose release from organosolv pretreated spruce and birch. The properties, inhibition kinetics and substrate specific activities for each enzyme are described in detail. The results show that a combination of EGs belonging to Glycosyl hydrolase families 5, 6, and 9, with a CBHI and CBHII in appropriate proportions, can enhance the production of COS from forest materials, underpinning the potential of these biocatalysts in the production of NDOs.

A bifunctional cellulase-xylanase of a new Chryseobacterium strain isolated from the dung of a straw-fed cattle

A new cellulolytic strain of Chryseobacterium genus was screened from the dung of a cattle fed with cereal straw. A putative cellulase gene (cbGH5) belonging to glycoside hydrolase family 5 subfamily 46 (GH5_46) was identified and cloned by degenerate PCR plus genome walking. The CbGH5 protein was overexpressed in Pichia pastoris, purified and characterized. It is the first bifunctional cellulase-xylanase reported in GH5_46 as well as in Chryseobacterium genus. The enzyme showed an endoglucanase activity on carboxymethylcellulose of 3237 μmol min-1  mg-1 at pH 9, 90 °C and a xylanase activity on birchwood xylan of 1793 μmol min-1  mg-1 at pH 8, 90 °C. The activity level and thermophilicity are in the front rank of all the known cellulases and xylanases. Core hydrophobicity had a positive effect on the thermophilicity of this enzyme. When similar quantity of enzymatic activity units was applied on the straws of wheat, rice, corn and oilseed rape, CbGH5 could obtain 3.5-5.0× glucose and 1.2-1.8× xylose than a mixed commercial cellulase plus xylanase of Novozymes. When applied on spent mushroom substrates made from the four straws, CbGH5 could obtain 9.2-15.7× glucose and 3.5-4.3× xylose than the mixed Novozymes cellulase+xylanase. The results suggest that CbGH5 could be a promising candidate for industrial lignocellulosic biomass conversion.

Recombinant expression of thermostable processive MtEG5 endoglucanase and its synergism with MtLPMO from Myceliophthora thermophila during the hydrolysis of lignocellulosic substrates

BACKGROUND

Filamentous fungi are among the most powerful cellulolytic organisms in terrestrial ecosystems. To perform the degradation of lignocellulosic substrates, these microorganisms employ both hydrolytic and oxidative mechanisms that involve the secretion and synergism of a wide variety of enzymes. Interactions between these enzymes occur on the level of saccharification, i.e., the release of neutral and oxidized products, but sometimes also reflected in the substrate liquefaction. Although the synergism regarding the yield of neutral sugars has been extensively studied, further studies should focus on the oxidized sugars, as well as the effect of enzyme combinations on the viscosity properties of the substrates.

RESULTS

In the present study, the heterologous expression of an endoglucanase (EG) and its combined activity together with a lytic polysaccharide monooxygenase (LPMO), both from the thermophilic fungus Myceliophthora thermophila, are described. The EG gene, belonging to the glycoside hydrolase family 5, was functionally expressed in the methylotrophic yeast Pichia pastoris. The produced MtEG5A (75 kDa) featured remarkable thermal stability and showed high specific activity on microcrystalline cellulose compared to CMC, which is indicative of its processivity properties. The enzyme was capable of releasing high amounts of cellobiose from wheat straw, birch, and spruce biomass. Addition of MtLPMO9 together with MtEG5A showed enhanced enzymatic hydrolysis yields against regenerated amorphous cellulose (PASC) by improving the release not only of the neutral but also of the oxidized sugars. Assessment of activity of MtEG5A on the reduction of viscosity of PASC and pretreated wheat straw using dynamic viscosity measurements revealed that the enzyme is able to perform liquefaction of the model substrate and the natural lignocellulosic material, while when added together with MtLPMO9, no further synergistic effect was observed.

CONCLUSIONS

The endoglucanase MtEG5A from the thermophilic fungus M. thermophila exhibited excellent properties that render it a suitable candidate for use in biotechnological applications. Its strong synergism with LPMO was reflected in sugars release, but not in substrate viscosity reduction. Based on the level of oxidative sugar formation, this is the first indication of synergy between LPMO and EG reported.

Characterization of a thermostable endoglucanase produced by Isoptericola variabilis sp. IDAH9

This study aimed to isolate and evaluate the cellulase activity of cellulolytic bacteria in hot springs of Dehloran, Ilam province, Iran. Water and sludge samples were collected from the hot springs and the bacterial enrichment was performed in a medium containing rice barn and carboxymethyl cellulose (CMC). The cultures were incubated at 50 °C in aerobic conditions. The bacteria were isolated on CMC agar (1%) medium. Cellulase assay of the isolates was measured by the evaluation of endoglucanase enzyme activity, which is also called as carboxymethyl cellulase (CMCase). The isolated thermotolerant bacteria were then identified and optimized for the production of CMCase. Moreover, stabilizing elements of the enzyme were identified with in silico approach. The chosen isolate was identified as Isoptericola variabilis sp. IDAH9. The identified strain produced the most thermostable CMCase at a concentration of 5.6 g/L of ammonium sulfate, 9 g/L CMCase or 12 g/L rice bran, 0/6% Tween-80, and 0.2% sucrose. The produced enzyme showed 80% of the residual activity after 1 h of incubation at 65 °C. In silico data indicated that the remaining residual activity was due to the redundant stabilizing elements in the protein structure. Consequently, I. variabilis can be isolated from the extreme environment and has a thermostable endoglucanase which may be used for various applications after studying them.

Lignocellulose degrading extremozymes produced by Pichia pastoris: current status and future prospects

In this review article, extremophilic lignocellulosic enzymes with special interest on xylanases, β-mannanases, laccases and finally cellulases, namely, endoglucanases, exoglucanases and β-glucosidases produced by Pichia pastoris are reviewed for the first time. Recombinant lignocellulosic extremozymes are discussed from the perspectives of their potential application areas; characteristics of recombinant and native enzymes; the effects of P. pastoris expression system on recombinant extremozymes; and their expression levels and applied strategies to increase the enzyme expression yield. Further, effects of enzyme domains on activity and stability, protein engineering via molecular dynamics simulation and computational prediction, and site-directed mutagenesis and amino acid modifications done are also focused. Superior enzyme characteristics and improved stability due to the proper post-translational modifications and better protein folding performed by P. pastoris make this host favourable for extremozyme production. Especially, glycosylation contributes to the structure, function and stability of enzymes, as generally glycosylated enzymes produced by P. pastoris exhibit better thermostability than non-glycosylated enzymes. However, there has been limited study on enzyme engineering to improve catalytic efficiency and stability of lignocellulosic enzymes. Thus, in the future, studies should focus on protein engineering to improve stability and catalytic efficiency via computational modelling, mutations, domain replacements and fusion enzyme technology. Also metagenomic data need to be used more extensively to produce novel enzymes with extreme characteristics and stability.

A thermostable GH26 endo-β-mannanase from Myceliophthora thermophila capable of enhancing lignocellulose degradation

The endomannanase gene em26a from the thermophilic fungus Myceliophthora thermophila, belonging to the glycoside hydrolase family 26, was functionally expressed in the methylotrophic yeast Pichia pastoris. The putative endomannanase, dubbed MtMan26A, was purified to homogeneity (60 kDa) and subsequently characterized. The optimum pH and temperature for the enzymatic activity of MtMan26A were 6.0 and 60 °C, respectively. MtMan26A showed high specific activity against konjac glucomannan and carob galactomannan, while it also exhibited high thermal stability with a half-life of 14.4 h at 60 °C. Thermostability is of great importance, especially in industrial processes where harsh conditions are employed. With the aim of better understanding its structure-function relationships, a homology model of MtMan26A was constructed, based on the crystallographic structure of a close homologue. Finally, the addition of MtMan26A as a supplement to the commercial enzyme mixture Celluclast® 1.5 L and Novozyme® 188 resulted in enhanced enzymatic hydrolysis of pretreated beechwood sawdust, improving the release of total reducing sugars and glucose by 13 and 12 %, respectively.

Development of Thermophilic Tailor-Made Enzyme Mixtures for the Bioconversion of Agricultural and Forest Residues

Even though the main components of all lignocellulosic feedstocks include cellulose, hemicellulose, as well as the protective lignin matrix, there are some differences in structure, such as in hardwoods and softwoods, which may influence the degradability of the materials. Under this view, various types of biomass might require a minimal set of enzymes that has to be tailor-made. Partially defined complex mixtures that are currently commercially used are not adapted to efficiently degrade different materials, so novel enzyme mixtures have to be customized. Development of these cocktails requires better knowledge about the specific activities involved, in order to optimize hydrolysis. The role of filamentous fungus Myceliophthora thermophila and its complete enzymatic repertoire for the bioconversion of complex carbohydrates has been widely proven. In this study, four core cellulases (MtCBH7, MtCBH6, MtEG5, and MtEG7), in the presence of other four "accessory" enzymes (mannanase, lytic polyssacharide monooxygenase MtGH61, xylanase, MtFae1a) and β-glucosidase MtBGL3, were tested as a nine-component cocktail against one model substrate (phosphoric acid swollen cellulose) and four hydrothermally pretreated natural substrates (wheat straw as an agricultural waste, birch, and spruce biomass, as forest residues). Synergistic interactions among different enzymes were determined using a suitable design of experiments methodology. The results suggest that for the hydrolysis of the pure substrate (PASC), high proportions of MtEG7 are needed for efficient yields. MtCBH7 and MtEG7 are enzymes of major importance during the hydrolysis of pretreated wheat straw, while MtCBH7 plays a crucial role in case of spruce. Cellobiohydrolases MtCBH6 and MtCBH7 act in combination and are key enzymes for the hydrolysis of the hardwood (birch). Optimum combinations were predicted from suitable statistical models which were able to further increase hydrolysis yields, suggesting that tailor-made enzyme mixtures targeted toward a particular residual biomass can help maximize hydrolysis yields. The present work demonstrates the change from "one cocktail for all" to "tailor-made cocktails" that are needed for the efficient saccharification of targeted feed stocks prior to the production of biobased products through the biorefinery concept.

A Novel GH7 Endo-β-1,4-Glucanase from Neosartorya fischeri P1 with Good Thermostability, Broad Substrate Specificity and Potential Application in the Brewing Industry

An endo-β-1,4-glucanase gene, cel7A, was cloned from the thermophilic cellulase-producing fungus Neosartorya fischeri P1 and expressed in Pichia pastoris. The 1,410-bp full-length gene encodes a polypeptide of 469 amino acids consisting of a putative signal peptide at residues 1–20, a catalytic domain of glycoside hydrolase family 7 (GH7), a short Thr/Ser-rich linker and a family 1 carbohydrate-binding module (CBM 1). The purified recombinant Cel7A had pH and temperature optima of pH 5.0 and 60°C, respectively, and showed broad pH adaptability (pH 3.0–6.0) and excellent stability at pH3.0–8.0 and 60°C. Belonging to the group of nonspecific endoglucanases, Cel7A exhibited the highest activity on barley β-glucan (2020 ± 9 U mg^–1), moderate on lichenan and CMC-Na, and weak on laminarin, locust bean galactomannan, Avicel, and filter paper. Under simulated mashing conditions, addition of Cel7A (99 μg) reduced the mash viscosity by 9.1% and filtration time by 24.6%. These favorable enzymatic properties make Cel7A as a good candidate for applications in the brewing industry.

Heterologous Expression and Characterization of a GH3 β-Glucosidase from Thermophilic Fungi Myceliophthora thermophila in Pichia pastoris

A novel β-glucosidase of glycoside hydrolase (GH) family 3 from Myceliophthora thermophila (mtbgl3b) was successfully expressed in Pichia pastoris. The full-length gene consists of 2613 bp nucleotides encoding a protein of 870 amino acids. MtBgl3b showed maximum activity at pH 5.0 and remained more than 70 % relative activity at 3.5-6.0. The enzyme displayed the highest activity at 60 °C and kept about 90 % relative activity for 50-65 °C; besides, the enzyme showed psychrophilic trait and remains 51 % relative activity at 40 °C. MtBgl3b exhibited good stability over a wide pH range of 3.0-10.0 and was thermostable at 60 and 65 °C. The enzyme displayed highest activity towards p-nitrophenyl-β-D-glucopyranoside (pNPG), followed by p-nitrophenyl-D-cellobioside (pNPC), cellotetraose, cellotriose, cellobiose, and gentiobiose. When using 10 % cellobiose (w/v) as the substrate, the enzyme showed transglycosylation activity to produce the cellotriose. The kinetic parametric of K m and V max were 2.78 mM and 927.9 μM mg(-1) min(-1), respectively. Finally, the reaction mode of the enzyme and the substrates were analyzed by molecular docking approach.

Site-Directed Mutagenesis of a Hyperthermophilic Endoglucanase Cel12B from Thermotoga maritima Based on Rational Design

To meet the demand for the application of high activity and thermostable cellulases in the production of new-generation bioethanol from nongrain-cellulose sources, a hyperthermostable β-1,4-endoglucase Cel12B from Thermotoga maritima was selected for further modification by gene site-directed mutagenesis method in the present study, based on homology modeling and rational design. As a result, two recombinant enzymes showed significant improvement in enzyme activity by 77% and 87%, respectively, higher than the parental enzyme TmCel12B. Furthermore, the two mutants could retain 80% and 90.5% of their initial activity after incubation at 80°C for 8 h, while only 45% for 5 h to TmCel12B. The Km and Vmax of the two recombinant enzymes were 1.97±0.05 mM, 4.23±0.15 μmol·mg(-1)·min(-1) of TmCel12B-E225H-K207G-D37V, and 2.97±0.12 mM, 3.15±0.21 μmol·mg(-1)·min(-1) of TmCel12B-E225H-K207G, respectively, when using CMC-Na as the substrate. The roles of the mutation sites were also analyzed and evaluated in terms of electron density, hydrophobicity of the modeled protein structures. The recombinant enzymes may be used in the hydrolysis of cellulose at higher temperature in the future. It was concluded that the gene mutagenesis approach of a certain active residues may effectively improve the performance of cellulases for the industrial applications and contribute to the study the thermostable mechanism of thermophilic enzymes.

Development of genetic tools for Myceliophthora thermophila

Background

The thermophilic filamentous fungus Myceliophthora thermophila has many suitable characteristics for industrial biotechnology and could be a promising new chassis system for synthetic biology, particularly the ATCC 42464 strain, whose genome was sequenced in 2011. However, metabolic engineering of this strain using genetic approaches has not been reported owing to a lack of genetic tools for this organism.

Results

In the present study, we developed a high efficiency Agrobacterium tumefaciens mediated transformation system for M. thermophila, including an approach for targeted gene deletion using green fluorescence protein (GFP) as a marker for selection. Up to 145 transformants per 10⁵ conidia were obtained in one transformation plate. Moreover, a ku70 deletion mutant was constructed in the ATCC 42464 background using the tools developed in present study and subsequently characterized. The ku70 deletion construct was designed using resistance to phosphinothricin as the selection marker. Additionally, a GFP-encoding cassette was incorporated that allowed for the selection of site-specific (no fluorescence) or ectopic (fluorescence) integration of the ku70 construct. Transformants with ectopically integrated ku70 deletion constructs were therefore identified using the fluorescent signal of GFP. PCR and Southern blotting analyses of non-fluorescent putative ku70 deletion transformants revealed all 11 tested transformants to be correct deletions. The deletion frequency in a pool of 116 transformants analyzed was 58 %. Moreover, the homologous rate improved about 3 folds under ku70 mutant using the pyrG as a test gene to disrupt in M. thermophila.

Conclusions

We successfully developed an efficient transformation and target gene disruption approach for M. thermophila ATCC 42464 mediated by A. tumefaciens. The tools and the ku70 deletion strain developed here should advance the development of M. thermophila as an industrial host through metabolic engineering and accelerate the elucidation of the mechanism of rapid cellulose degradation in this thermophilic fungus.

Myceliophthora thermophila syn. Sporotrichum thermophile: a thermophilic mould of biotechnological potential

Myceliophthora thermophila syn. Sporotrichum thermophile is a ubiquitous thermophilic mould with a strong ability to degrade organic matter during optimal growth at 45 °C. Both genome analysis and experimental data have suggested that the mould is capable of hydrolyzing all major polysaccharides found in biomass. The mould is able to secrete a large number of hydrolytic enzymes (cellulases, laccases, xylanases, pectinases, lipases, phytases and some other miscellaneous enzymes) employed in various biotechnological applications. Characterization of the biomass-hydrolyzing activity of wild and recombinant enzymes suggests that this mould is highly efficient in biomass decomposition at both moderate and high temperatures. The native enzymes produced by the mould are more efficient in activity than their mesophilic counterparts beside their low enzyme titers. The mould is able to synthesize various biomolecules, which are used in multifarious applications. Genome sequence data of M. thermophila also supported the physiological data. This review describes the biotechnological potential of thermophilic mould, M. thermophila supported by genomic and experimental evidences.

Genomic insights into the fungal lignocellulolytic system of Myceliophthora thermophila

The microbial conversion of solid cellulosic biomass to liquid biofuels may provide a renewable energy source for transportation fuels. Cellulolytic fungi represent a promising group of organisms, as they have evolved complex systems for adaptation to their natural habitat. The filamentous fungus Myceliophthora thermophila constitutes an exceptionally powerful cellulolytic microorganism that synthesizes a complete set of enzymes necessary for the breakdown of plant cell wall. The genome of this fungus has been recently sequenced and annotated, allowing systematic examination and identification of enzymes required for the degradation of lignocellulosic biomass. The genomic analysis revealed the existence of an expanded enzymatic repertoire including numerous cellulases, hemicellulases, and enzymes with auxiliary activities, covering the most of the recognized CAZy families. Most of them were predicted to possess a secretion signal and undergo through post-translational glycosylation modifications. These data offer a better understanding of activities embedded in fungal lignocellulose decomposition mechanisms and suggest that M. thermophila could be made usable as an industrial production host for cellulolytic and hemicellulolytic enzymes.

Transcriptome and exoproteome analysis of utilization of plant-derived biomass by Myceliophthora thermophila

Myceliophthora thermophila is a thermophilic fungus whose genome encodes a wide range of carbohydrate-active enzymes (CAZymes) involved in plant biomass degradation. Such enzymes have potential applications in turning different kinds of lignocellulosic feedstock into sugar precursors for biofuels and chemicals. The present study examined and compared the transcriptomes and exoproteomes of M. thermophila during cultivation on different types of complex biomass to gain insight into how its secreted enzymatic machinery varies with different sources of lignocellulose. In the transcriptome analysis three monocot (barley, oat, triticale) and three dicot (alfalfa, canola, flax) plants were used whereas in the proteome analysis additional substrates, i.e. wood and corn stover pulps, were included. A core set of 59 genes encoding CAZymes was up-regulated in response to both monocot and dicot straws, including nine polysaccharide monooxygenases and GH10, but not GH11, xylanases. Genes encoding additional xylanolytic enzymes were up-regulated during growth on monocot straws, while genes encoding additional pectinolytic enzymes were up-regulated in response to dicot biomass. Exoproteome analysis was generally consistent with the conclusions drawn from transcriptome analysis, but additional CAZymes that accumulated to high levels were identified. Despite the wide variety of biomass sources tested some CAZy family members were not expressed under any condition. The results of this study provide a comprehensive view from both transcriptome and exoproteome levels, of how M. thermophila responds to a wide range of biomass sources using its genomic resources.