Expression of multi-functional cellulase gene mfc in Coprinus cinereus under control of different basidiomycete promoters

Current perspective on production and applications of microbial cellulases: a review

The potential of cellulolytic enzymes has been widely studied and explored for bioconversion processes and plays a key role in various industrial applications. Cellulase, a key enzyme for cellulose-rich waste feedstock-based biorefinery, has increasing demand in various industries, e.g., paper and pulp, juice clarification, etc. Also, there has been constant progress in developing new strategies to enhance its production, such as the application of waste feedstock as the substrate for the production of individual or enzyme cocktails, process parameters control, and genetic manipulations for enzyme production with enhanced yield, efficiency, and specificity. Further, an insight into immobilization techniques has also been presented for improved reusability of cellulase, a critical factor that controls the cost of the enzyme at an industrial scale. In addition, the review also gives an insight into the status of the significant application of cellulase in the industrial sector, with its techno-economic analysis for future applications. The present review gives a complete overview of current perspectives on the production of microbial cellulases as a promising tool to develop a sustainable and greener concept for industrial applications.

Identification of a Heat-Inducible Element of Cysteine Desulfurase Gene Promoter in Lentinula edodes

Volatile organosulfur compounds are the main components that contribute to the unique aroma of dried Lentinula edodes. They are mainly generated during the hot-air drying process, and cysteine desulfurase is the key enzyme in this process. Temperature may be an essential factor of volatile organosulfur compound production by influencing the expression of the cysteine desulfurase gene. In this study, the promoter sequence of the cysteine desulfurase gene (pCS) was cloned and analyzed using bioinformatics tools. A series of 5′deletion fragments and site-directed mutations of pCS were constructed to identify the element that responds to heat stress. Six heat shock transcription factor (HSTF) binding sites were predicted by SCPD (The Promoter Database of Saccharomyces cerevisiae) and three of the binding sites were predicted by Yeastract (Yeast Search for Transcriptional Regulators and Consensus Tracking) in pCS. The results indicated that pCS was able to drive the expression of the EGFP (Enhanced Green Fluorescent Protein) gene in L. edodes. Moreover, the fluorescence intensity increased after heat stress. The changes in fluorescence intensity of different 5′deletion fragments showed that the heat response region was located between −500 bp and −400 bp in pCS. The site-directed mutation analysis further showed that the heat-inducible element was between −490 bp and −500 bp (TTTCTAGAAT) in pCS. Our results provide molecular insight for studying the formation of volatile organosulfur compounds in dried L. edodes.

A novel thermostable GH10 xylanase with activities on a wide variety of cellulosic substrates from a xylanolytic Bacillus strain exhibiting significant synergy with commercial Celluclast 1.5 L in pretreated corn stover hydrolysis

BACKGROUND

Cellulose and hemicellulose are the two largest components in lignocellulosic biomass. Enzymes with activities towards cellulose and xylan have attracted great interest in the bioconversion of lignocellulosic biomass, since they have potential in improving the hydrolytic performance and reducing the enzyme costs. Exploring glycoside hydrolases (GHs) with good thermostability and activities on xylan and cellulose would be beneficial to the industrial production of biofuels and bio-based chemicals.

RESULTS

A novel GH10 enzyme (XynA) identified from a xylanolytic strain Bacillus sp. KW1 was cloned and expressed. Its optimal pH and temperature were determined to be pH 6.0 and 65 °C. Stability analyses revealed that XynA was stable over a broad pH range (pH 6.0-11.0) after being incubated at 25 °C for 24 h. Moreover, XynA retained over 95% activity after heat treatment at 60 °C for 60 h, and its half-lives at 65 °C and 70 °C were about 12 h and 1.5 h, respectively. More importantly, in terms of substrate specificity, XynA exhibits hydrolytic activities towards xylans, microcrystalline cellulose (filter paper and Avicel), carboxymethyl cellulose (CMC), cellobiose, p-nitrophenyl-β-d-cellobioside (pNPC), and p-nitrophenyl-β-d-glucopyranoside (pNPG). Furthermore, the addition of XynA into commercial cellulase in the hydrolysis of pretreated corn stover resulted in remarkable increases (the relative increases may up to 90%) in the release of reducing sugars. Finally, it is worth mentioning that XynA only shows high amino acid sequence identity (88%) with rXynAHJ14, a GH10 xylanase with no activity on CMC. The similarities with other characterized GH10 enzymes, including xylanases and bifunctional xylanase/cellulase enzymes, are no more than 30%.

CONCLUSIONS

XynA is a novel thermostable GH10 xylanase with a wide substrate spectrum. It displays good stability in a broad range of pH and high temperatures, and exhibits activities towards xylans and a wide variety of cellulosic substrates, which are not found in other GH10 enzymes. The enzyme also has high capacity in saccharification of pretreated corn stover. These characteristics make XynA a good candidate not only for assisting cellulase in lignocellulosic biomass hydrolysis, but also for the research on structure-function relationship of bifunctional xylanase/cellulase.

Laccase production and pellet morphology of Coprinopsis cinerea transformants in liquid shake flask cultures

Laccase production and pellet formation of transformants of Coprinopsis cinerea strain FA2222 of C. cinerea laccase gene lcc1 subcloned behind the gpdII-promoter from Agaricus bisporus were compared with a control transformant carrying no extra laccase gene. At the optimum growth temperature of 37 °C, maximal laccase yields of 2.9 U/ml were obtained by the best lcc1 transformant pYSK7-26 in liquid shake flask cultures. Reduction in temperature to 25 °C increased laccase yields up to 9.2 U/ml. The control transformant had no laccase activities at 37 °C but native activity at 25 °C (3.5 U/ml). Changing the temperature had severe effects on the morphology of the mycelial pellets formed during cultivation, but links of distinct pellet morphologies to native or recombinant laccase production could not be established. Automated image analysis was used to characterise pellet formation and morphological parameters (pellet area, diameter, convexity and mycelial structure). Cross sections of selected pellets showed that they differentiated in an outer rind and an inner medulla of loosened hyphae. Pellets at 25 °C had a small and dense outer zone and adopted with time a smooth surface. Pellets at 37 °C had a broader outer zone and a fringy surface due to generation of more and larger protuberances in the rind that when released can serve for production of further pellets.

Combining sestc engineered A. niger with sestc engineered S. cerevisiae to produce rice straw ethanol via step-by-step and in situ saccharification and fermentation

The development of agricultural residue ethanol has a profound effect on the environment protection and energy supply. To increase the production efficiency of straw ethanol and reduce operation progress, the single-enzyme-system-three-cellulase gene (sestc) engineered Aspergillus niger and sestc engineered Saccharomyces cerevisiae were combined to produce ethanol using the pretreated rice straw as the substrate. The present results showed that both the step-by-step and in situ saccharification and fermentation can effectively produce ethanol using rice straw as the carbon substrate. The conversion rates of ethanol were 12.76 and 14.56 g per 1 kg of treated rice straw, respectively, via step-by-step and in situ processes. In situ process has higher ethanol conversion efficiency of rice straw and fewer operation processes as compared with step-by-step process. Therefore, in situ saccharification and fermentation is a more economical and effective pathway to convert rice straw into ethanol. This study provides a reference to the conversion of lignocellulosic residues into ethanol with a combination of two kinds of sestc engineered strains.

Construction of recombinant sestc Saccharomyces cerevisiae for consolidated bioprocessing, cellulase characterization, and ethanol production by in situ fermentation

Bioethanol is an important oil substitute produced by the sugar fermentation process. To improve the efficiency of cellulase expression of Saccharomyces cerevisiae, a eukaryotic expression vector harboring a single-enzyme-system-three-cellulase gene (sestc) was integrated into the S. cerevisiae genome by the protoplast method. Using PCR screening, RT-PCR, and “transparent circle” detection, several recombinant S. cerevisiae strains, capable of efficiently expressing the heterogeneous cellulase, were selected. The total activity of cellulase, endo-β-D-glucanase, exo-β-D-glucanase, and xylanase of the recombinant S. cerevisiae transformant (designated number 14) was 1.1, 378, 1.44, and 164 U ml⁻¹, respectively, which was 27.5-, 63-, 24-, and 19-fold higher than that of the wild-type strain. The concentration of ethanol produced by the engineered S. cerevisiae strain was 8.1 gl⁻¹, with wheat bran as the carbon source, under submerged conditions; this was 57.86-fold higher than that produced by the wild-type strain (0.14 gl⁻¹).

Construction of Aspergillus niger integrated with cellulase gene from Ampullaria gigas Spix for improved enzyme production and saccharification of alkaline-pretreated rice straw

Aspergillus niger is an important microorganism that has been used for decades to produce extracellular enzymes. In this study, a novel Aspergillus niger strain integrated with a eukaryotic expression vector harboring the gpd-Shi promoter of shiitake mushrooms and cellulase gene of Ampullaria gigas Spix was engineered to improve cellulase production for the achievement of highly efficient saccharification of agricultural residues. In one strain, designated ACShi27, which exhibited the highest total cellulase expression, total cellulase, endoglucanase, exoglucanase, and xylanase expression levels were 1.73, 16.23, 17.73, and 150.83 U ml⁻¹, respectively; these values were 14.5, 22.3, 24.6, and 17.3% higher than those of the wild-type Aspergillus niger M85 using wheat bran as an induction substrate. Production of cellulases and xylanase by solid-state fermentation followed by in situ saccharification of ACShi27 was investigated with alkaline-pretreated rice straw as a substrate. After 2 days of enzyme induction at 30 °C, followed by 48 h of saccharification at 50 °C, the conversion rate of carbon polymers into reducing sugar reached 293.2 mg g⁻¹, which was 1.23-fold higher than that of the wild-type strain. The expression of sestc in Aspergillus niger can improve the total cellulase and xylanase activity and synergism, thereby enhancing the lignocellulose in situ saccharification.

Paradoxical performance of tryptophan synthase gene trp1 (+) in transformations of the basidiomycete Coprinopsis cinerea

Several transformation strains of Coprinopsis cinerea carry the defective tryptophan synthase allele trp1-1,1-6 which can be complemented by introduction of the trp1 (+) wild-type gene. Regularly in C. cinerea, single-trp1 (+)-vector transformations yield about half the numbers of clones than cotransformations with a non-trp1 (+)-plasmid done in parallel. The effect is also observed with the orthologous Schizophyllum commune trpB (+) gene shown here to function as a selection marker in C. cinerea. Parts of single-trp1 (+) - or single-trpB (+) -vector transformants are apparently lost. This paradoxical phenomenon relates to de-regulation of aromatic amino acid biosynthesis pathways. Adding tryptophan precursors to protoplast regeneration agar or feeding with other aromatic amino acids increases loss of single-trp1 (+)-vector transformants and also sets off loss of clones in cotransformation with a non-trp1 (+)-plasmid. Feedback control by tryptophan and cross-pathway control by tyrosine and phenylalanine are both active in the process. We deduce from the observations that more cotransformants than single-vector transformants are obtained by in average less disturbance of the tryptophan biosynthesis pathway. DNA in C. cinerea transformation usually integrates into the genome at multiple ectopic places. Integration events for a single vector per nucleus should statistically be 2-fold higher in single-vector transformations than in cotransformations in which the two different molecules compete for the same potential integration sites. Integration of more trp1 (+) copies into the genome might more likely lead to sudden tryptophan overproduction with subsequent rigid shut-down of the pathway. Blocking ectopic DNA integration in a Δku70 mutant abolished the effect of doubling clone numbers in cotransformations due to preferred single trp1 (+) integration by homologous recombination at its native genomic site.

Production of antibacterial peptide from bee venom via a new strategy for heterologous expression

Honey bee is important economic insect that not only pollinates fruits and crops but also provides products with various physiological activities. Bee venom is a functional agent that is widely applied in clinical treatment and pharmacy. Secapin is one of these agents that have a significant role in therapy. The functions of secapin from the bee venom have been documented, but little information is known about its heterologous expression under natural condition. Moreover, few scholars verified experimentally the functions of secapin from bee venom in vitro. In this study, we successfully constructed a heterologous expression vector, which is different from conventional expression system. A transgenic approach was established for transformation of secapin gene from the venom of Apis mellifera carnica (Ac-sec) into the edible fungi, Coprinus cinereus. Ac-sec was encoded by a 234 bp nucleotide that contained a signal peptide domain and two potential phosphorylation sites. The sequence exhibited highly homology with various secapins characterized from honey bee and related species. Southern blot data indicated that Ac-sec was present as single or multiple copy loci in the C. cinereus genome. By co-transformation and double-layer active assay, Ac-sec was expressed successfully in C. cinereus and the antibacterial activity of the recombinants was identified, showing notable antibacterial activities on different bacteria. Although Ac-sec is from the venom of Apidae, phylogenetic analysis demonstrated that Ac-sec was more closely related to that of Vespid than to bee species from Apidae. The molecular characteristics of Ac-sec and the potential roles of small peptides in biology were discussed.

Bioproduction of baccatin III, an advanced precursor of paclitaxol, with transgenic Flammulina velutipes expressing the 10-deacetylbaccatin III-10-O-acetyl transferase gene

BACKGROUND

10-Deacetylbaccatin III (10-DAB) and baccatin III are intermediates in the biosynthesis of Taxol (an anti-cancer drug) and useful precursors for semi-synthesis of the drug. In this study, a bioconversion system was established for the production of baccatin III, an advanced precursor of paclitaxel, in the transgenic mushroom Flammulina velutipes expressing the 10-deacetylbaccatin III-10β-O-acetyltransferase gene. The expression vector pgFvs-TcDBAT containing the 10-deacetylbaccatin III-10β-O-acetyltransferase (DBAT) gene was constructed and transformed into the cells of F. velutipes by polyethylene glycol-mediated protoplast transformation.

RESULTS

Polymerase chain reaction and Southern blotting analysis verified the successful integration of the exogenous DBAT gene into the genome of F. velutipes. Reverse transcription polymerase chain reaction and enzyme activity analyses confirmed that the DBAT gene was expressed in F. velutipes, and DBAT is able to convert substrate into baccatin III.

CONCLUSION

The DBAT gene from the plant Taxus chinensis can be functionally expressed in F. velutipes. Transgenic F. velutipes expressing the DBAT gene is able to produce the target product, baccatin III. This is the first report about the transformation and expression of paclitaxel biosynthetic gene in the edible mushroom F. velutipes. This represents a significant step towards bio-production of paclitaxel and its advanced precursor baccatin III in an edible fungus.

Overproduction of geranylgeraniol in Coprinopsis cinerea by the expression of geranylgeranyl diphosphate synthase gene

(E, E, E)-Geranylgeraniol (GGOH) is a valuable ingredient of many perfumes and a valuable precursor for synthesizing pharmaceuticals. In an attempt to increase the GGOH concentration in Coprinopsis cinerea, we demonstrated that the expression of geranylgeranyl diphosphate synthase (ggpps) gene isolated from Taxus x media could promote GGOH production. Furthermore, the concentrations of squalene and ergosterol were measured in the engineered strains. Expectedly, significant decreases of squalene and ergosterol levels were observed in those strains transformed with ggpps gene. This could be explained by the partial redirection of metabolic flux from squalene to GGOH, whose biosynthesis competes for the same precursor with squalene. This work suggested that the expression of ggpps in higher fungi was an effective method for bio-production of GGOH.

Enhancement of heterologous gene expression in Flammulina velutipes using polycistronic vectors containing a viral 2A cleavage sequence

Agrobacterium tumefaciens-mediated transformation for edible mushrooms has been previously established. However, the enhancement of heterologous protein production and the expression of multi-target genes remains a challenge. In this study, heterologous protein expression in the enoki mushroom Flammulina velutipes was notably enhanced using 2A peptide-mediated cleavage to co-express multiple copies of single gene. The polycistronic expression vectors were constructed by connecting multi copies of the enhanced green fluorescent protein (egfp) gene using 2A peptides derived from porcine teschovirus-1. The P2A peptides properly self-cleaved as shown by the formation of the transformants with antibiotic resistant capacity and exciting green fluorescence levels after introducing the vectors into F. velutipes mycelia. The results of western blot analysis, epifluorescent microscopy and EGFP production showed that heterologous protein expression in F. velutipes using the polycistronic strategy increased proportionally as the gene copy number increased from one to three copies. In contrast, much lower EGFP levels were detected in the F. velutipes transformants harboring four copies of the egfp gene due to mRNA instability. The polycistronic strategy using 2A peptide-mediated cleavage developed in this study can not only be used to express single gene in multiple copies, but also to express multiple genes in a single reading frame. It is a promising strategy for the application of mushroom molecular pharming.

Agrobacterium tumefaciens mediated fused egfp-hph gene expression under the control of gpd promoter in Pleurotus ostreatus

A transformation system for the basidiomycete Pleurotus ostreatus was established using agrobacterium-mediated infection. Following P. ostreatus glyceraldehyde-3-phosphate dehydrogenase gene analysis, its promoter region including two introns was used as cis-regulatory element to drive expression of enhanced green fluorescent protein (eGFP). As a selection marker, the hygromycin phosphotransferase (hph) gene cassette was used in the binary vector pPEH. Mycelia without pretreatment were found to be the most efficient recipients in transformation experiments while fruiting body tissue or basidiospores showed lower transformation rates. A transformation efficiency of 75% was achieved. After subculturing, putative transformants were screened by PCR and Southern blot analysis showing the expected ectopic integration of the transforming DNA. At the same time, the promotor region was shown to drive expression of selection marker as well as eGFP that could be visualized, which will be helpful for future investigation using Agrobacterium tumefaciens mediated transformation for functional characterization of genes in the mushroom forming basidioymcete P. ostreatus.

Heterologous expression of the immunomodulatory protein gene from Ganoderma sinense in the basidiomycete Coprinopsis cinerea

AIMS

FIP-gsi, a fungal immunomodulatory protein found in Ganoderma sinense, has antitumour, anti-allergy and immunomodulatory activities and is regulated by the fip-gsi gene. In this study, we aimed to express the fip-gsi gene from G. sinense in Coprinopsis cinerea to increase yield of FIPs-gsi.

METHODS AND RESULTS

A fungal expression vector pBfip-gsi containing the gpd promoter from Agaricus bisporus and the fip-gsi gene from the G. sinense was constructed and transformed into C. cinerea. PCR and Southern blotting analysis verified the successful integration of the exogenous gene fip-gsi into the genome of C. cinerea. RT-PCR and Northern blotting analysis confirmed that the fip-gsi gene was transcribed in C. cinerea. The yield of the FIP-gsi protein reached 314mg kg(-1) fresh mycelia. The molecular weight of the FIP-gsi was 13kDa, and the FIP-gsi was capable of hemagglutinating mouse red blood cells, but no such activity was observed towards human red blood cells in vitro.

CONCLUSIONS

The fip-gsi from G. sinense has been successfully translated in C. cinerea, and the yield of bioactive FIP-gsi protein was high.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report using the C. cinerea for the heterologous expression of FIP-gsi protein and it might supply a basis for large-scale production of the protein.