Gene cloning and heterologous expression of a novel endoglucanase, swollenin, from Trichoderma pseudokoningii S38

Towards an understanding of the enzymatic degradation of complex plant mannan structures

Plant cell walls are composed of a heterogeneous mixture of polysaccharides that require several different enzymes to degrade. These enzymes are important for a variety of biotechnological processes, from biofuel production to food processing. Several classical mannanolytic enzyme functions of glycoside hydrolases (GH), such as β-mannanase, β-mannosidase and α-galactosidase activities, are helpful for efficient mannan hydrolysis. In this light, we bring three enzymes into the model of mannan degradation that have received little or no attention. By linking their three-dimensional structures and substrate specificities, we have predicted the interactions and cooperativity of these novel enzymes with classical mannanolytic enzymes for efficient mannan hydrolysis. The novel exo-β-1,4-mannobiohydrolases are indispensable for the production of mannobiose from the terminal ends of mannans, this product being the preferred product for short-chain mannooligosaccharides (MOS)-specific β-mannosidases. Second, the side-chain cleaving enzymes, acetyl mannan esterases (AcME), remove acetyl decorations on mannan that would have hindered backbone cleaving enzymes, while the backbone cleaving enzymes liberate MOS, which are preferred substrates of the debranching and sidechain cleaving enzymes. The nonhydrolytic expansins and swollenins disrupt the crystalline regions of the biomass, improving their accessibility for AcME and GH activities. Finally, lytic polysaccharide monooxygenases have also been implicated in promoting the degradation of lignocellulosic biomass or mannan degradation by classical mannanolytic enzymes, possibly by disrupting adsorbed mannan residues. Modelling effective enzymatic mannan degradation has implications for improving the saccharification of biomass for the synthesis of value-added and upcycling of lignocellulosic wastes.

Effects on Capsicum annuum Plants Colonized with Trichoderma atroviride P. Karst Strains Genetically Modified in Taswo1, a Gene Coding for a Protein with Expansin-like Activity

Here, we analyzed the effects on Capsicum annuum plants of Trichoderma atroviride P. Karst strains altered in the expression of SWOLLENIN (SWO1), a protein with amorphogenic activity on plant cell wall components. Strains of T. atroviride that overexpressed the Taswo1 gene were constructed as well as deletion mutants. A novel, cheap and accurate method for assessing root colonization was developed. Colonization assays showed that the Taswo1 overexpressing strains invaded the host root better than the WT, resulting in a stronger plant growth-promoting effect. The expression of plant defense marker genes for both the systemic acquired resistance and induced systemic resistance pathways was enhanced in plants inoculated with Taswo1 overexpressing strains, while inoculation with deletion mutant strains resulted in a similar level of expression to that observed upon inoculation with the wild-type strain. Response to pathogen infection was also enhanced in the plants inoculated with the Taswo1 overexpressing strains, and surprisingly, an intermediate level of protection was achieved with the mutant strains. Tolerance to abiotic stresses was also higher in plants inoculated with the Taswo1 overexpressing strains but was similar in plants inoculated with the wild-type or the mutant strains. Compatible osmolyte production in drought conditions was studied. This study may contribute to improving Trichoderma biocontrol and biofertilization abilities.

A Swollenin From Talaromyces leycettanus JCM12802 Enhances Cellulase Hydrolysis Toward Various Substrates

Swollenins exist within some fungal species and are candidate accessory proteins for the biodegradation of cellulosic substrates. Here, we describe the identification of a swollenin gene, Tlswo, in Talaromyces leycettanus JCM12802. Tlswo was successfully expressed in both Trichoderma reesei and Pichia pastoris. Assay results indicate that TlSWO is capable of releasing reducing sugars from lichenan, barley β-glucan, carboxymethyl cellulose sodium (CMC-Na) and laminarin. The specific activity of TlSWO toward lichenan, barley β-glucan, carboxymethyl cellulose sodium (CMC-Na) and laminarin is 9.0 ± 0.100, 8.9 ± 0.100, 2.3 ± 0.002 and 0.79 ± 0.002 U/mg, respectively. Additionally, TlSWO had disruptive activity on Avicel and a synergistic effect with cellobiohydrolases, increasing the activity on pretreated corn stover by up to 72.2%. The functional diversity of TlSWO broadens its applicability in experimental settings, and indicating that it may be a promising candidate for future industrial applications.

TgSWO from Trichoderma guizhouense NJAU4742 promotes growth in cucumber plants by modifying the root morphology and the cell wall architecture

BACKGROUND

Colonization of Trichoderma spp. is essential for exerting their beneficial functions on the plant. However, the interactions between Trichoderma spp. and plant roots are still not completely understood. The aim of this study was to investigate how TgSWO affect Trichoderma guizhouense to establish themselves in the plant rhizosphere and promote plant growth. In this study, we deeply analyzed the molecular mechanism by which the functional characterization of the TgSWO by expressing different functional region deletion proteins (FRDP) of TgSWO.

RESULTS

Root scanning analysis results showed that TgSWO could dramatically increase root density and promote growth. In addition, we also found that TgSWO could expand root cell walls, subsequently increase root colonization. Moreover, knockout of TgSWO mutants (KO) or overexpression of TgSWO mutants (OE) produced greatly reduced or increased the number of cucumber root, respectively. To clarify the molecular mechanism of TgSWO in plant-growth-promotion, we analyzed the ability of different FRDP to expand the root cell wall. The root cell wall architecture were considerably altered when treated by ΔCBD protein (the TgSWO gene of lacking in the CBD domain was cloned and heterologously expressed), in correlation with the present YoaJ domain of TgSWO. In contrast, neither the expansion of cell walls nor the increase of roots was detectable in ΔYoaJ protein.

CONCLUSIONS

Our results emphasize the YoaJ domain is the most critical functional area of TgSWO during the alteration of cell wall architecture. Simultaneously, the results obtained in this study also indicate that TgSWO might play a plant-growth-promotion role in the Trichoderma-plant interactions by targeting the root cell wall.

Bacterial expansins and related proteins from the world of microbes

The discovery of microbial expansins emerged from studies of the mechanism of plant cell growth and the molecular basis of plant cell wall extensibility. Expansins are wall-loosening proteins that are universal in the plant kingdom and are also found in a small set of phylogenetically diverse bacteria, fungi, and other organisms, most of which colonize plant surfaces. They loosen plant cell walls without detectable lytic activity. Bacterial expansins have attracted considerable attention recently for their potential use in cellulosic biomass conversion for biofuel production, as a means to disaggregate cellulosic structures by nonlytic means ("amorphogenesis"). Evolutionary analysis indicates that microbial expansins originated by multiple horizontal gene transfers from plants. Crystallographic analysis of BsEXLX1, the expansin from Bacillus subtilis, shows that microbial expansins consist of two tightly packed domains: the N-terminal domain D1 has a double-ψ β-barrel fold similar to glycosyl hydrolase family-45 enzymes but lacks catalytic residues usually required for hydrolysis; the C-terminal domain D2 has a unique β-sandwich fold with three co-linear aromatic residues that bind β-1,4-glucans by hydrophobic interactions. Genetic deletion of expansin in Bacillus and Clavibacter cripples their ability to colonize plant tissues. We assess reports that expansin addition enhances cellulose breakdown by cellulase and compare expansins with distantly related proteins named swollenin, cerato-platanin, and loosenin. We end in a speculative vein about the biological roles of microbial expansins and their potential applications. Advances in this field will be aided by a deeper understanding of how these proteins modify cellulosic structures.

A novel expansin protein from the white-rot fungus Schizophyllum commune

A novel expansin protein (ScExlx1) was found, cloned and expressed from the Basidiomycete fungus Schizophylum commune. This protein showed the canonical features of plant expansins. ScExlx1 showed the ability to form “bubbles” in cotton fibers, reduce the size of avicel particles and enhance reducing sugar liberation from cotton fibers pretreated with the protein and then treated with cellulases. ScExlx1 was able to bind cellulose, birchwood xylan and chitin and this property was not affected by different sodium chloride concentrations. A novel property of ScExlx1 is its capacity to enhance reducing sugars (N-acetyl glucosamine) liberation from pretreated chitin and further added with chitinase, which has not been reported for any expansin or expansin-like protein. To the best of our knowledge, this is the first report of a bona fide fungal expansin found in a basidiomycete and we could express the bioactive protein in Pichia pastoris.

A novel non-hydrolytic protein from Pseudomonas oryzihabitans enhances the enzymatic hydrolysis of cellulose

Several kinds of protein such as the expansin, expansin-like proteins and LPMOs (lytic polysaccharide monooxygenases) are known to exert enhancement effects on cellulase activity. In this study, a novel cellulase synergistic protein named POEP1 was purified from the culture filtrate of Pseudomonas oryzihabitans CGMCC 6169, and was homogeneous on SDS-PAGE with a molecular weight of 60kDa. Mass spectrometry analysis indicated that it was an unknown protein without sequence similarity to the expansin and expansin-like proteins. Evaluation of the enzymatic hydrolysis of filter paper revealed that POEP1 had no cellulase activity but displayed high synergistic activity of 364% at a cellulase concentration of 0.1FPU/g of filter paper. When a mixture containing 0.6FPU cellulase and 700μg POEP1 per g of cellulose was evaluated, the maximal sugar yield was achieved, which was 2.2-fold greater than that with the cellulase alone. POEP1 was found to have functional similarity to the expansin and expansin-like proteins, which could decrease both the hydrogen-bond intensity and crystallinity, and cause the filter paper disruption. This study provided evidence for the existence of novel bacterial proteins in nature serving the same function as expansin and expansin-like proteins.

Towards a carbon-negative sustainable bio-based economy

The bio-based economy relies on sustainable, plant-derived resources for fuels, chemicals, materials, food and feed rather than on the evanescent usage of fossil resources. The cornerstone of this economy is the biorefinery, in which renewable resources are intelligently converted to a plethora of products, maximizing the valorization of the feedstocks. Innovation is a prerequisite to move a fossil-based economy toward sustainable alternatives, and the viability of the bio-based economy depends on the integration between plant (green) and industrial (white) biotechnology. Green biotechnology deals with primary production through the improvement of biomass crops, while white biotechnology deals with the conversion of biomass into products and energy. Waste streams are minimized during these processes or partly converted to biogas, which can be used to power the processing pipeline. The sustainability of this economy is guaranteed by a third technology pillar that uses thermochemical conversion to valorize waste streams and fix residual carbon as biochar in the soil, hence creating a carbon-negative cycle. These three different multidisciplinary pillars interact through the value chain of the bio-based economy.

Characterization of a novel swollenin from Penicillium oxalicum in facilitating enzymatic saccharification of cellulose

Background

Plant expansins and fungal swollenin that can disrupt crystalline cellulose have great potential for applications in conversion of biomass. Recent studies have been mainly focused on Trichoderma reesei swollenin that show relatively low activity in the promotion of cellulosic hydrolysis. Our aim was to isolate a novel swollenin with greater disruptive activity, to establish an efficient way of producing recombinant swollenin, and to optimize the procedure using swollenin in facilitation of cellulosic hydrolysis.

Results

A novel gene encoding a swollenin-like protein, POSWOI, was isolated from the filamentous fungus Penicillium oxalicum by Thermal Asymmetric Interlaced PCR (TAIL-PCR). It consisted of a family 1 carbohydrate-binding module (CBM1) followed by a linker connected to a family 45 endoglucanase-like domain. Using the cellobiohydrolase I promoter, recombinant POSWOI was efficiently produced in T. reesei with a yield of 105 mg/L, and showed significant disruptive activity on crystalline cellulose. Simultaneous reaction with both POSWOI and cellulases enhanced the hydrolysis of crystalline cellulose Avicel by approximately 50%. Using a POSWOI-pretreatment procedure, cellulases can produce nearly twice as many reducing sugars as without pretreatment. The mechanism by which POSWOI facilitates the saccharification of cellulose was also studied using a cellulase binding assay.

Conclusion

We present a novel fungal swollenin with considerable disruptive activity on crystalline cellulose, and develop a better procedure for using swollenin in facilitating cellulosic hydrolysis. We thus provide a new approach for the effective bioconversion of cellulosic biomass.

Effect of codon optimization on the expression of Trichoderma reesei endoglucanase 1 in Pichia pastoris

Trichoderma reesei cellulases are important biocatalysts for a wide range of industrial applications that include the paper, feed, and textile industries. T. reesei endoglucanase 1 (egl1) was successfully expressed as an active and stable catalyst in Pichia pastoris for the first time. Codon optimization was applied to egl1 of T. reesei to enhance its expression levels in P. pastoris. When compared with the originally cloned egl1 gene of T. reesei, the synthetic codon optimized egl1 gene (egl1s) was expressed at a higher level in P. pastoris. Batch fermentations of both clones with the same copy number under controlled conditions indicated that codon optimized EGI enzyme activity increased to 1.24 fold after 72 h of methanol induction. Our research indicated that P. pastoris is a suitable host for cellulase production.

High-level expression and efficient purification of bioactive swollenin in Aspergillus oryzae

The bioactivity of swollenin is beneficial to cellulose decomposition by cellulase despite the lack of hydrolytic activity itself. In order to improve the productivity of swollenin, the effects of culture conditions on the expression level in recombinant Aspergillus oryzae were investigated systematically. With regard to the bioactivity of swollenin, glycerin and peanut meal were the optimal carbon or nitrogen source, respectively. The highest level production of swollenin (50 mg L(-1)) was attained after 88 h cultivation with the initial pH of 5.6 in the culture medium. Then the soluble swollenin was effectively purified from the cultural supernatant by ammonium sulfate precipitation and cationic exchange chromatography with recovery yield of 53.2%. The purified swollenin was fully bioactive due to its strong synergistic activity with cellulose.

Access to cellulose limits the efficiency of enzymatic hydrolysis: the role of amorphogenesis

The efficient enzymatic saccharification of cellulose at low cellulase (protein) loadings continues to be a challenge for commercialization of a process for bioconversion of lignocellulose to ethanol. Currently, effective pretreatment followed by high enzyme loading is needed to overcome several substrate and enzyme factors that limit rapid and complete hydrolysis of the cellulosic fraction of biomass substrates. One of the major barriers faced by cellulase enzymes is their limited access to much of the cellulose that is buried within the highly ordered and tightly packed fibrillar architecture of the cellulose microfibrils. Rather than a sequential 'shaving' or 'planing' of the cellulose fibrils from the outside, it has been suggested that these inaccessible regions are disrupted or loosened by non-hydrolytic proteins, thereby increasing the cellulose surface area and making it more accessible to the cellulase enzyme complex. This initial stage in enzymatic saccharification of cellulose has been termed amorphogenesis. In this review, we describe the various amorphogenesis-inducing agents that have been suggested, and their possible role in enhancing the enzymatic hydrolysis of cellulose.

Endoglucanase activities and growth of marine-derived fungi isolated from the sponge Haliclona simulans

AIMS

The conversion of cheap cellulosic biomass to more easily fermentable sugars requires the use of costly cellulases. We have isolated a series of marine sponge-derived fungi and screened these for cellulolytic activity to determine the potential of this unique environmental niche as a source of novel cellulase activities.

METHODS AND RESULTS

Fungi were isolated from the marine sponge Haliclona simulans. Phylogenetic analysis of these and other fungi previously isolated from H. simulans showed fungi from three phyla with very few duplicate species. Cellulase activities were determined using plate-based assays using different media and sea water concentrations while extracellular cellulase activities were determined using 3,5-dinitrosalicylic acid (DNSA)-based assays. Total and specific cellulase activities were determined using a range of incubation temperatures and compared to those for the cellulase overproducing mutant Hypocrea jecorina QM9414. Several of the strains assayed produced total or relative endoglucanase activities that were higher than H. jecorina, particularly at lower reaction temperatures.

CONCLUSIONS

Marine sponges harbour diverse fungal species and these fungi are a good source of endoglucanase activities. Analysis of the extracellular endoglucanase activities revealed that some of the marine-derived fungi produced high endoglucanase activities that were especially active at lower temperatures.

SIGNIFICANCE AND IMPACT OF THE STUDY

Marine-derived fungi associated with coastal marine sponges are a novel source of highly active endoglucanases with significant activity at low temperatures and could be a source of novel cellulase activities.

Transcriptional profiling of cellulase and expansin-related genes in a hypercellulolytic Trichoderma reesei

Expression kinetics of six cellulase and four expansin-related genes were studied in the hypercellulolytic Trichoderma reesei CL847 mutant in response to Solka Floc cellulose and soluble inducers. Real-time PCR showed a parallel increase of transcript levels for the cellulase genes cbh1/cel7a, egl1/cel7b, egl4/cel61a, the beta-glucosidase genes bgl1/cel3a, bgl2/cel1a, and the swo1 gene, encoding the cell-wall loosening protein swollenin. To evaluate a putative implication of three newly identified expansin/family 45 endoglucanase-like (EEL) proteins in lignocellulose degradation, their expression was also analysed. Only eel2 was found to be transcribed under the present conditions, and showed constitutive expression similar to the endoglucanase encoding cel5b gene.