Production of cellulases and hemicellulases by three Penicillium species: effect of substrate and evaluation of cellulase adsorption by capillary electrophoresis

A Novel Cellobiohydrolase I (CBHI) from Penicillium digitatum: Production, Purification, and Characterization

A new cellulase producer strain of Penicillium digitatum (RV 06) was previously obtained from rotten maize grains. This work aim was to optimize the production and characterize this microorganism produced cellulase. A CMCase maximum production (1.6 U/mL) was obtained in stationary liquid culture, with an initial pH of 5.0, at 25 °C, with 1% lactose as carbon source, and cultured for 5 days. The produced enzyme was purified by ammonium sulfate precipitation and exclusion chromatography. The purified enzyme optimal temperature and pH were 60 °C and 5.2, respectively. The experimental T_m of thermal inactivation was 63.68 °C, and full activity was recovered after incubation of 7 h at 50 °C. The purified 74 kDa CMCase presented K_M for CMC of 11.2 mg/mL, V_max of 0.13 μmol/min, k_cat of 52 s^-1, and k_cat/K_M of 4.7 (mg/mL)^-1 s^-1. The purified enzyme had a high specificity for CMC and p-nitrophenyl cellobioside and released glucose and cellobiose as final products of the CMC hydrolysis. The enzyme trypsin digestion produced peptides whose masses were obtained by MALDI-TOF/TOF mass spectrometry, which was also used to obtain two peptide sequences. These peptide sequences and the mass peak profile retrieved a CBHI within the annotated genome of P. digitatum PD1. Sequence alignments and phylogenetic analysis confirmed this enzyme as a CBHI of the glycoside hydrolase family 7. The P. digitatum PD1 protein in silico structural model revealed a coil and β-conformation predominance, which was confirmed by circular dichroism of the P. digitatum RV 06 purified enzyme.

DNA Stable-Isotope Probing Delineates Carbon Flows from Rice Residues into Soil Microbial Communities Depending on Fertilization

Decomposition of crop residues in soil is mediated by microorganisms whose activities vary with fertilization. The complexity of active microorganisms and their interactions utilizing residues is impossible to disentangle without isotope applications. Thus, 13C-labeled rice residues were employed, and DNA stable-isotope probing (DNA-SIP) combined with high-throughput sequencing was applied to identify microbes active in assimilating residue carbon (C). Manure addition strongly modified microbial community compositions involved in the C flow from rice residues. Relative abundances of the bacterial genus Lysobacter and fungal genus Syncephalis were increased, but abundances of the bacterial genus Streptomyces and fungal genus Trichoderma were decreased in soils receiving mineral fertilizers plus manure (NPKM) compared to levels in soils receiving only mineral fertilizers (NPK). Microbes involved in the flow of residue C formed a more complex network in NPKM than in NPK soils because of the necessity to decompose more diverse organic compounds. The fungal species (Jugulospora rotula and Emericellopsis terricola in NPK and NPKM soils, respectively) were identified as keystone species in the network and may significantly contribute to residue C decomposition. Most of the fungal genera in NPKM soils, especially Chaetomium, Staphylotrichum, Penicillium, and Aspergillus, responded faster to residue addition than those in NPK soils. This is connected with the changes in the composition of the rice residue during degradation and with fungal adaptation (abundance and activity) to continuous manure input. Our findings provide fundamental information about the roles of key microbial groups in residue decomposition and offer important cues on manipulating the soil microbiome for residue utilization and C sequestration in soil.IMPORTANCE Identifying and understanding the active microbial communities and interactions involved in plant residue utilization are key questions to elucidate the transformation of soil organic matter (SOM) in agricultural ecosystems. Microbial community composition responds strongly to management, but little is known about specific microbial groups involved in plant residue utilization and, consequently, microbial functions under different methods of fertilization. We combined DNA stable-isotope (13C) probing and high-throughput sequencing to identify active fungal and bacterial groups degrading residues in soils after 3 years of mineral fertilization with and without manure. Manuring changed the active microbial composition and complexified microbial interactions involved in residue C flow. Most fungal genera, especially Chaetomium, Staphylotrichum, Penicillium, and Aspergillus, responded to residue addition faster in soils that historically had received manure. We generated a valuable library of microorganisms involved in plant residue utilization for future targeted research to exploit specific functions of microbial groups in organic matter utilization and C sequestration.

A review on commercial-scale high-value products that can be produced alongside cellulosic ethanol

The demand for fossil derivate fuels and chemicals has increased, augmenting concerns on climate change, global economic stability, and sustainability on fossil resources. Therefore, the production of fuels and chemicals from alternative and renewable resources has attracted considerable and growing attention. Ethanol is a promising biofuel that can reduce the consumption of gasoline in the transportation sector and related greenhouse gas (GHG) emissions. Lignocellulosic biomass is a promising feedstock to produce bioethanol (cellulosic ethanol) because of its abundance and low cost. Since the conversion of lignocellulose to ethanol is complex and expensive, the cellulosic ethanol price cannot compete with those of the fossil derivate fuels. A promising strategy to lower the production cost of cellulosic ethanol is developing a biorefinery which produces ethanol and other high-value chemicals from lignocellulose. The selection of such chemicals is difficult because there are hundreds of products that can be produced from lignocellulose. Multiple reviews and reports have described a small group of lignocellulose derivate compounds that have the potential to be commercialized. Some of these products are in the bench scale and require extensive research and time before they can be industrially produced. This review examines chemicals and materials with a Technology Readiness Level (TRL) of at least 8, which have reached a commercial scale and could be shortly or immediately integrated into a cellulosic ethanol process.

Screening of potential IL-tolerant cellulases and their efficient saccharification of IL-pretreated lignocelluloses

Lignocellulosic biomass as one of the most abundant and renewable resources has great potential for biofuel production. The complete conversion of biomass to biofuel is achieved through the effective pretreatment process and the following enzyme saccharification. Ionic liquids (ILs) are considered as a green solvent for lignocellulose pretreatment. However, ILs exhibit an inhibitory effect on cellulase activity, leading to a subsequent decrease in the efficiency of saccharification. The screening of new potential IL-tolerant cellulases is important. In the current study, a fungal strain with a relatively high cellulase production was isolated and identified as Penicillium oxalicum HC6. The culture conditions were optimized using corn stover and peptone as the carbon source and nitrogen source at pH 4.0 and 30 °C with an inoculation size of 2% (v/v) for 8 days. It was found that P. oxalicum HC6 exhibited potential salt tolerance with the increase of the enzyme production at a salt concentration of 5.0% (w/v). In addition, high enzyme activities were obtained at pH 4.0–6.0 and 50–65 °C. The crude enzyme from P. oxalicum HC6 with good thermal stability was also stable in the presence of salt and ILs. Good yields of reducing sugar were obtained by the crude enzyme from P. oxalicum HC6 after the saccharification of corn stover that was pretreated by ILs. P. oxalicum HC6 with potentially salt-tolerant and IL-tolerant enzymes has great potential application in the enzymatic saccharification of lignocellulose.

Lignocellulosic biomass as one of the most abundant and renewable resources has great potential for biofuel production.

Efficient yeast cell-surface display of an endoglucanase of Aspergillus flavus and functional characterization of the whole-cell enzyme

The endoglucanase gene endo753 from Aspergillus flavus NRRL3357 strains was cloned, and the recombinant Endo753 was displayed on the cell surface of Saccharomyces cerevisiae EBY100 strain by the C-terminal fusion using Aga2p protein as anchor attachment tag. The results of indirect immunofluorescence and Western blot confirmed the expression and localization of Endo753 on the yeast cell surface. The hydrolytic activity test of the whole-cell enzyme revealed that Endo753 immobilized on the yeast cell surface had high endoglucanase activity. The functional characterization of the whole-cell enzyme was investigated, and the whole-cell enzyme displayed the maximum activity at pH 8 and 50 °C. The enzyme was stable in a pH range of 7.0-10.0. Furthermore, the whole-cell enzyme displayed high thermostability below 50 °C and moderate stability between 50 and 70 °C. These properties make endo753 a good candidate in bioethanol production from lignocellulosic materials after displaying on the yeast cell surface.

Optimization of cellulase production by Penicillium sp

The production of cellulolytic enzymes (β-exoglucanase, β-endoglucanase and β-glucosidase) by Penicillium sp. on three different media in liquid shake culture conditions was compared. The organism exhibited relatively highest activity of endoglucanase among three enzymes measured at 7-day interval during the course of its growth on Czapek-Dox medium supplemented with 0.5 % (w/v) cellulose. Cellulose at 0.5 %, lactose at 0.5 %, sawdust at 0.5 %, yeast extract at 0.2 % as a nitrogen source, pH 5.0 and 30 °C temperature were found to be optimal for growth and cellulase production by Penicillium sp. Yields of Fpase, CMCase and β-glucosidase, attained on optimized medium with Penicillium sp. were 8.7, 25 and 9.52 U/ml, respectively with increment of 9.2, 5.9 and 43.8-folds over titers of the respective enzyme on unoptimised medium. Cellulase of the fungal culture with the ratio of β-glucosidase to Fpase greater than one will hold potential for biotechnological applications.

A novel bZIP transcription factor ClrC positively regulates multiple stress responses, conidiation and cellulase expression in Penicillium oxalicum

Cellulase production in filamentous fungi is largely regulated at the transcriptional level, and several transcription factors have been reported to be involved in this process. In this study, we identified ClrC, a novel transcription factor in cellulase production in Penicillium oxalicum. ClrC and its orthologs have a highly conserved basic leucine zipper (bZIP) DNA binding domain, and their biological functions have not been explored. Deletion of clrC resulted in pleiotropic effects, including altered growth, reduced conidiation and increased sensitivity to oxidative and cell wall stresses. In particular, the clrC deletion mutant ΔclrC showed 46.1% ± 8.1% and 58.0% ± 8.7% decreases in production of filter paper enzyme and xylanase activities in cellulose medium, respectively. In contrast, 57.4% ± 10.0% and 70.9% ± 19.4% increased production of filter paper enzyme, and xylanase was observed in the clrC overexpressing strain, respectively. The transcription levels of major cellulase genes, as well as two cellulase transcriptional activator genes, clrB and xlnR, were significantly downregulated in ΔclrC, but substantially upregulated in clrC overexpressing strains. Furthermore, we observed that the absence of ClrC reduced full induction of cellulase expression even in the clrB overexpressing strain. These results indicated that ClrC is a novel and efficient engineering target for improving cellulolytic enzyme production in filamentous fungi.

Characterization of oil-palm trunk residue degradation enzymes derived from the isolated fungus, Penicillium rolfsii c3-2(1) IBRL

This study characterizes crude enzymes derived from Penicillium rolfsii c3-2(1) IBRL, a mesophilic fungus isolated from the local soil of Malaysia. Prior to enzyme activity evaluation, P. rolfsii c3-2(1) IBRL was inoculated into a broth medium containing oil-palm trunk residues for the preparation of crude enzymes. Oil-palm trunk residues were optimally hydrolysed at pH5.0 and 50°C. P. rolfsii c3-2(1) IBRL-derived crude enzymes displayed higher thermal stability compared with the commercial enzymes, Celluclast 1.5 L and Acellerase 1500. Moreover, the hydrolysing activities of the P. rolfsii c3-2(1) IBRL-derived crude enzymes (xylan, arabinan, and laminarin) were superior compared to that of Celluclast 1.5 L and Acellerase 1500, and exhibit 2- to 3-fold and 3- to 4-fold higher oil-palm trunk residues-hydrolysing specific activity, respectively. This higher hydrolysis efficiency may be attributed to the weak 'lignin-binding' ability of the P. rolfsii c3-2(1) IBRL-derived enzymes compared to the commercial enzymes.

Mutagenesis and evaluation of cellulase properties and cellulose hydrolysis of Talaromyces piceus

A fungal species with a high yield of β-glucosidase was isolated and identified as Talaromyces piceus 9-3 (anamorph: Penicillium piceum) by morphological and molecular characterization. Through dimethyl sulphate mutagenesis, the cellulase over-producing strain T. piceus H16 was obtained. The FPase activity and β-glucosidase activity of T. piceus H16 were 5.83 and 53.12 IU ml(-1) respectively--a 5.34- and 4.43-times improvement from the parent strain T. piceus 9-3. The optimum pH and temperature for enzyme activity were pH 5.0 and 50 °C for FPase activity and pH 5.0 and 55 °C for β-glucosidase activity, respectively. The cellulase were quite stable at 37 °C, only losing <10% of their initial activity after 24 h of incubation. Hydrolysis analysis results showed that a highly efficient synergistic effect was achieved by combining cellulase from T. piceus H16 with that from Trichoderma reesei RUT C30 on hydrolyzing different substrates due to the high β-glucosidase activity of T. piceus H16. These data suggest that T. piceus H16 can be used as a potential cellulase producer with good prospects.

Novel pH-Stable Glycoside Hydrolase Family 3 β-Xylosidase from Talaromyces amestolkiae: an Enzyme Displaying Regioselective Transxylosylation

This paper reports on a novel β-xylosidase from the hemicellulolytic fungus Talaromyces amestolkiae. The expression of this enzyme, called BxTW1, could be induced by beechwood xylan and was purified as a glycoprotein from culture supernatants. We characterized the gene encoding this enzyme as an intronless gene belonging to the glycoside hydrolase gene family 3 (GH3). BxTW1 exhibited transxylosylation activity in a regioselective way. This feature would allow the synthesis of oligosaccharides or other compounds not available from natural sources, such as alkyl glycosides displaying antimicrobial or surfactant properties. Regioselective transxylosylation, an uncommon combination, makes the synthesis reproducible, which is desirable for its potential industrial application. BxTW1 showed high pH stability and Cu(2+) tolerance. The enzyme displayed a pI of 7.6, a molecular mass around 200 kDa in its active dimeric form, and Km and Vmax values of 0.17 mM and 52.0 U/mg, respectively, using commercial p-nitrophenyl-β-d-xylopyranoside as the substrate. The catalytic efficiencies for the hydrolysis of xylooligosaccharides were remarkably high, making it suitable for different applications in food and bioenergy industries.

Optimization of cellulase production by Penicillium oxalicum using banana agrowaste as a substrate

The purpose of this study was to produce a higher amount of cellulase by using an alternative carbon source, such as banana agrowaste, and to optimize the fermentation parameters for a high yield. In the present study, cellulase-producing Penicillium was isolated from a decaying wood sample. Different nutritional and environmental factors were investigated to assess their effect on cellulase production. The highest crude enzyme production was observed at a pH 6.0 and a temperature of 28°C in a medium that was supplemented with banana agrowaste as the carbon source. Pretreatment with 2N NaOH, at 7% substrate (banana agrowaste) concentration yielded the highest cellulase activity. Further to this, the effect of other parameters such as inoculum age, inoculum size, static and agitated conditions were also studied. It is concluded that Penicillium oxalicum is a powerful cellulase-producer strain under our tested experimental conditions using banana agrowaste as the carbon source.

Population, diversity and characteristics of cellulolytic microorganisms from the Indo-Burma Biodiversity hotspot

Forest ecosystem harbour a large number of biotic components where cellulolytic microorganisms participate actively in the biotransformation of dead and decaying organic matter and soil nutrient cycling. This study explores the aerobic culturable cellulolytic microorganisms in the forest soils of North East India. Soil samples rich in dead and decaying organic matter were collected from eight conserved forests during the season when microbes were found to be most active. Cellulolytic microorganisms were isolated using selective media in which cellulose was the sole carbon source. Population of culturable, aerobic, cellulolytic microorganisms were found to be higher at the incubation temperature that corresponds to the natural ambient temperature of the site of sample collection. Bacterial population was higher in all of the sites than fungal population. Bacterial population ranged from 1.91 × 10(5) to 3.35 × 10(6) CFU g(-1) dry soil while actinomycetes and fungal population ranged from 9.13 × 10(2) to 3.46 × 10(4) CFU g(-1) dry soil and 9.36 × 10(2) to 4.31 × 10(4) CFU g(-1) dry soil, respectively. It was observed that though many isolates showed activity on the CMC plate assay, very few isolates showed significant filter paper activity. Three cellulolytic fungal isolates showing high FPase activity were characterised, identified and submitted to GenBank as Talaromyces verruculosus SGMNPf3 (KC937053), Trichoderma gamsii SGSPf7 (KC937055) and Trichoderma atroviride SGBMf4 (KC937054).

Genome shuffling of Aspergillus glaucus HGZ-2 for enhanced cellulase production

The production of cellulase from Aspergillus glaucus HGZ-2 was improved by using genome shuffling. The starting populations, obtained by UV irradiation, were subjected to recursive protoplast fusion. The optimal conditions for protoplast formation and regeneration were 7 mg/ml snailase and 5 mg/ml cellulase at 34 °C for 3.0 h using 0.7 M NaCl as an osmotic stabilizer. The protoplasts were inactivated under UV for 30 min or heated at 50 °C for 50 min, and a fusant probability of about 100 % was observed. The positive colonies were created by fusing the inactivated protoplasts. The optimal conditions for protoplast fusion were PEG6000 concentration of 35 %, CaCl2 concentration of 0.02 M, and incubation time of 12 min. After two rounds of genome shuffling, one strain (Y) was obtained. Its filter paper cellulase (FPase) and carboxymethyl cellulase (CMCase) activity reached 71 and 70 U/ml, respectively, which were increased by 1.95-fold and 1.72-fold in comparison with that of its ancestor strain. The results indicated that genome shuffling was an efficient means for the improved production of cellulases by A. glaucus HGZ-2.

Optimisation of Cellulase Production by Penicillium funiculosum in a Stirred Tank Bioreactor Using Multivariate Response Surface Analysis

Increasing interest in the production of second-generation ethanol necessitates the low-cost production of enzymes from the cellulolytic complex (endoglucanases, exoglucanases, and β-glucosidases), which act synergistically in cellulose breakdown. The present work aimed to optimise a bioprocess to produce these biocatalysts from the fungus Penicillium funiculosum ATCC11797. A statistical full factorial design (FFD) was employed to determine the optimal conditions for cellulase production. The optimal composition of culture media using Avicel (10 g·L⁻¹) as carbon source was determined to include urea (1.2 g·L⁻¹), yeast extract (1.0 g·L⁻¹), KH₂PO₄ (6.0 g·L⁻¹), and MgSO₄·7H₂O (1.2 g·L⁻¹). The growth process was performed in batches in a bioreactor. Using a different FFD strategy, the optimised bioreactor operational conditions of an agitation speed of 220 rpm and aeration rate of 0.6 vvm allowed the obtainment of an enzyme pool with activities of 508 U·L⁻¹ for FPase, 9,204 U·L⁻¹ for endoglucanase, and 2,395 U·L⁻¹ for β-glucosidase. The sequential optimisation strategy was effective and afforded increased cellulase production in the order from 3.6 to 9.5 times higher than production using nonoptimised conditions.

Functional characterization of protein kinase CK2 regulatory subunits regulating Penicillium oxalicum asexual development and hydrolytic enzyme production

Casein kinase CK2 is a ubiquitous and conserved phosphate transferase that is critical for the growth and development of eukaryotic cells. In Penicillium oxalicum, one catalytic subunit (CK2A) and two regulatory subunits (CK2B1 and CK2B2) of CK2 were annotated. In this study, CK2 regulatory subunit-defective mutants Δck2B1 and Δck2B2 were constructed to investigate the biological function of CK2 in P. oxalicum. The Δck2B1 strain exhibited minimal changes in morphogenesis and conidiation, whereas the Δck2B2 strain showed delayed conidial germination and drastically reduced conidiation compared with the parent strain. The defect in conidiation in Δck2B2 could be attributed to the reduced expression of transcription factor BrlA. Both Δck2B1 and Δck2B2 showed delayed autolysis in carbon-starvation medium compared with the parent strain. Cellulase and amylase production were decreased considerably in both mutants. The transcript abundances of the main extracellular glycoside hydrolase genes cel7A-2, bgl1, and amy15A, as well as those of three related transcriptional activators (i.e., ClrB, XlnR, and AmyR), were reduced or delayed in the mutants. Epistasis analysis suggested that CK2B1 and CK2B2 might function upstream of transcription factor CreA by inhibiting its repressing activity. In summary, CK2 plays important roles in development and extracellular enzyme production in P. oxalicum, with both unique and overlapping functions performed by the two regulatory subunits.

Insights into high-efficiency lignocellulolytic enzyme production by Penicillium oxalicum GZ-2 induced by a complex substrate

BACKGROUND

Agricultural residue is more efficient than purified cellulose at inducing lignocellulolytic enzyme production in Penicillium oxalicum GZ-2, but in Trichoderma reesei RUT-C30, cellulose induces a more efficient response. To understand the reasons, we designed an artificially simulated plant biomass (cellulose plus xylan) to study the roles and relationships of each component in the production of lignocellulolytic enzymes by P. oxalicum GZ-2.

RESULTS

The changes in lignocellulolytic enzyme activity, gene expression involving (hemi)cellulolytic enzymes, and the secretome of cultures grown on Avicel (A), xylan (X), or a mixture of both (AX) were studied. The addition of xylan to the cellulose culture did not affect fungal growth but significantly increased the activity of cellulase and hemicellulase. In the AX treatment, the transcripts of cellulase genes (egl1, egl2, egl3, sow, and cbh2) and hemicellulase genes (xyl3 and xyl4) were significantly upregulated (P <0.05). The proportion of biomass-degrading proteins in the secretome was altered; in particular, the percentage of cellulases and hemicellulases was increased. The percentage of cellulases and hemicellulases in the AX secretome increased from 4.5% and 7.6% to 10.3% and 21.8%, respectively, compared to the secretome of the A treatment. Cellobiohydrolase II (encoded by cbh2) and xylanase II (encoded by xyl2) were the main proteins in the secretome, and their corresponding genes (cbh2 and xyl2) were transcripted at the highest levels among the cellulolytic and xylanolytic genes. Several important proteins such as swollenin, cellobiohydrolase, and endo-beta-1,4-xylanase were only induced by AX. Bray-Curtis similarity indices, a dendrogram analysis, and a diversity index all demonstrated that the secretome produced by P. oxalicum GZ-2 depended on the substrate and that strain GZ-2 directionally adjusted the compositions of lignocellulolytic enzymes in its secretome to preferably degrade a complex substrate.

CONCLUSION

The addition of xylan to the cellulose medium not only induces more hemicellulases but also strongly activates cellulase production. The proportion of the biomass-degrading proteins in the secretome was altered significantly, with the proportion of cellulases and hemicellulases especially increased. Xylan and cellulose have positively synergistic effects, and they play a key role in the induction of highly efficient lignocellulolytic enzymes.

Taxonomic revision of the cellulose-degrading fungus Acremonium cellulolyticus nomen nudum to Talaromyces based on phylogenetic analysis

The cellulase-producing fungal strain Y-94, isolated in Japan and invalidly described as Acremonium cellulolyticus nom. nud. strain Y-94, seldom forms enteroarthric conidia under nutrient starvation conditions. Phylogenetic analysis using ITS1-5.8S-ITS2 and RNA polymerase II large subunit gene sequences revealed that strain Y-94 is closely related to Talaromyces, given that these Y-94 sequences showed 100% identity with those of Talaromyces pinophilus NBRC 100533^T . By contrast, the identity between β-tubulin-encoding genes from strain Y-94 and T. pinophilus NBRC 100533^T was 98.1%. Morphological and phenotypic differences between these strains in colony color, conidiophore formation, and cellulase productivity were observed. Together, these data indicated that strain Y-94 belonged to the genus Talaromyces. We propose that strain Y-94 is a new species, Talaromyces cellulolyticus, on the basis of morphology and molecular evidence. The ex-holotype is Y-94 (= FERM BP-5826, CBS 136886 [holotype] TNS-F-48752).

Penicillium decumbens BrlA extensively regulates secondary metabolism and functionally associates with the expression of cellulase genes

Penicillium decumbens has been used in the industrial production of lignocellulolytic enzymes in China for more than 15 years. Conidiation is essential for most industrial fungi because conidia are used as starters in the first step of fermentation. To investigate the mechanism of conidiation in P. decumbens, we generated mutants defective in two central regulators of conidiation, FluG and BrlA. Deletion of fluG resulted in neither "fluffy" phenotype nor alteration in conidiation, indicating possible different upstream mechanisms activating brlA between P. decumbens and Aspergillus nidulans. Deletion of brlA completely blocked conidiation. Further investigation of brlA expression in different media (nutrient-rich or nutrient-poor) and different culture states (liquid or solid) showed that brlA expression is required but not sufficient for conidiation. The brlA deletion strain exhibited altered hyphal morphology with more branches. Genome-wide expression profiling identified BrlA-dependent genes in P. decumbens, including genes previously reported to be involved in conidiation as well as previously reported chitin synthase genes and acid protease gene (pepB). The expression levels of seven secondary metabolism gene clusters (from a total of 28 clusters) were drastically regulated in the brlA deletion strain, including a downregulated cluster putatively involved in the biosynthesis of the mycotoxins roquefortine C and meleagrin. In addition, the expression levels of most cellulase genes were upregulated in the brlA deletion strain detected by real-time quantitative PCR. The brlA deletion strain also exhibited an 89.1 % increase in cellulase activity compared with the wild-type strain. The results showed that BrlA in P. decumbens not only has a key role in regulating conidiation, but it also regulates secondary metabolism extensively as well as the expression of cellulase genes.

Increased production of cellulases and xylanases by Penicillium echinulatum S1M29 in batch and fed-batch culture

The development of more productive strains of microorganisms and processes that increase enzyme levels can contribute to the economically efficient production of second generation ethanol. To this end, cellulases and xylanases were produced with the S1M29 mutant strain of Penicillium echinulatum, using different concentrations of cellulose (20, 40, and 60 g L(-1)) in batch and fed-batch processes. The highest activities of FPase (8.3 U mL(-1)), endoglucanases (37.3 U mL(-1)), and xylanases (177 U mL(-1)) were obtained in fed-batch cultivation with 40 g L(-1) of cellulose. The P. echinulatum enzymatic broth and the commercial enzyme Cellic CTec2 were tested for hydrolysis of pretreated sugar cane bagasse. Maximum concentrations of glucose and xylose were achieved after 72 h of hydrolysis. Glucose yields of 28.0% and 27.0% were obtained using the P. echinulatum enzymatic extract and Cellic CTec2, respectively.

Cellulase and Xylanase Production by Penicillium echinulatum in Submerged Media Containing Cellulose Amended with Sorbitol

The present work investigated the use of sorbitol as a soluble carbon source, in association with cellulose, to produce cellulases and xylanases in submerged cultures of Penicillium echinulatum 9A02S1. Because cellulose is an insoluble carbon source, in cellulase production, there are some problems with rheology and oxygen transfer. The submerged fermentations containing media composed of 0, 0.25, 0.5, 0.75, and 1% (w/v) sorbitol and cellulose that were added at different times during the cultivation; 0.2% (w/v) soy bran; 0.1% (w/v) wheat bran; and a solution of salts. The highest filter paper activity (FPA) (1.95  ±  0.04 IU·mL⁻¹) was obtained on the seventh day in the medium containing 0.5% (w/v) sorbitol and 0.5% (w/v) cellulose added 24 h after the start of cultivation. However, the CMCases showed an activity peak on the sixth day (9.99 ± 0.75 IU·mL⁻¹) in the medium containing 0.75% (w/v) sorbitol and 0.75% (w/v) cellulose added after 12 h of cultivation. The xylanases showed the highest activity in the medium with 0.75% (w/v) sorbitol and 0.25% (w/v) cellulose added 36 h after the start of cultivation. This strategy enables the reduction of the cellulose concentration, which in high concentrations can cause rheological and oxygen transfer problems.

Enzyme affinity to cell types in wheat straw (Triticum aestivum L.) before and after hydrothermal pretreatment

BACKGROUND

Wheat straw used for bioethanol production varies in enzymatic digestibility according to chemical structure and composition of cell walls and tissues. In this work, the two biologically different wheat straw organs, leaves and stems, are described together with the effects of hydrothermal pretreatment on chemical composition, tissue structure, enzyme adhesion and digestion. To highlight the importance of inherent cell wall characteristics and the diverse effects of mechanical disruption and biochemical degradation, separate leaves and stems were pretreated on lab-scale and their tissue structures maintained mostly intact for image analysis. Finally, samples were enzymatically hydrolysed to correlate digestibility to chemical composition, removal of polymers, tissue composition and disruption, particle size and enzyme adhesion as a result of pretreatment and wax removal. For comparison, industrially pretreated wheat straw from Inbicon A/S was included in all the experiments.

RESULTS

Within the same range of pretreatment severities, industrial pretreatment resulted in most hemicellulose and epicuticular wax/cutin removal compared to lab-scale pretreated leaves and stems but also in most re-deposition of lignin on the surface. Tissues were furthermore degraded from tissues into individual cells while lab-scale pretreated samples were structurally almost intact. In both raw leaves and stems, endoglucanase and exoglucanase adhered most to parenchyma cells; after pretreatment, to epidermal cells in all the samples. Despite heavy tissue disruption, industrially pretreated samples were not as susceptible to enzymatic digestion as lab-scale pretreated leaves while lab-scale pretreated stems were the least digestible.

CONCLUSIONS

Despite preferential enzyme adhesion to epidermal cells after hydrothermal pretreatment, our results suggest that the single most important factor determining wheat straw digestibility is the fraction of parenchyma cells rather than effective tissue disruption.

Production and characterization of acidophilic xylanolytic enzymes from Penicillium oxalicum GZ-2

Multiple acidophilic xylanolytic enzymes were produced by Penicillium oxalicum GZ-2 during growth on wheat straw, rice straw, corn stover, and wheat bran. The expression of xylanase isoforms was dependent on substrate type and nitrogen source. The zymograms produced by the SDS-PAGE resolution of the crude enzymes indicated that wheat straw was the best inducer, resulting in the highest xylanase (115.2U/mL) and β-xylosidase (89mU/mL) activities during submerged fermentation. The optimum temperature and pH for xylanase activity were 50°C and 4.0, respectively; however, the crude xylanase enzymes exhibited remarkable stability over a broad pH range and showed more than 90% activity at 50°C for 30min at pH 4.0-8.0. The results revealed that P. oxalicum GZ-2 is a promising acidophilic xylanase-producing microorganism that has great potential to be used in biofuels, animal feed, and food industry applications.

Optimisation of synergistic biomass-degrading enzyme systems for efficient rice straw hydrolysis using an experimental mixture design

Synergistic enzyme system for the hydrolysis of alkali-pretreated rice straw was optimised based on the synergy of crude fungal enzyme extracts with a commercial cellulase (Celluclast™). Among 13 enzyme extracts, the enzyme preparation from Aspergillus aculeatus BCC 199 exhibited the highest level of synergy with Celluclast™. This synergy was based on the complementary cellulolytic and hemicellulolytic activities of the BCC 199 enzyme extract. A mixture design was used to optimise the ternary enzyme complex based on the synergistic enzyme mixture with Bacillus subtilis expansin. Using the full cubic model, the optimal formulation of the enzyme mixture was predicted to the percentage of Celluclast™: BCC 199: expansin=41.4:37.0:21.6, which produced 769 mg reducing sugar/g biomass using 2.82 FPU/g enzymes. This work demonstrated the use of a systematic approach for the design and optimisation of a synergistic enzyme mixture of fungal enzymes and expansin for lignocellulosic degradation.

Performance of hemicellulolytic enzymes in culture supernatants from a wide range of fungi on insoluble wheat straw and corn fiber fractions

Filamentous fungi are a good source of hemicellulolytic enzymes for biomass degradation. Enzyme preparations were obtained as culture supernatants from 78 fungal isolates grown on wheat straw as carbon source. These enzyme preparations were utilized in the hydrolysis of insoluble wheat straw and corn fiber xylan rich fractions. Up to 14% of the carbohydrates in wheat straw and 34% of those in corn fiber were hydrolyzed. The degree of hydrolysis by the enzymes depended on the origin of the fungal isolate and on the complexity of the substrate to be degraded. Penicillium, Trichoderma or Aspergillus species, and some non-identified fungi proved to be the best producers of hemicellulolytic enzymes for degradation of xylan rich materials. This study proves that the choice for an enzyme preparation to efficiently degrade a natural xylan rich substrate, is dependent on the xylan characteristics and could not be estimated by using model substrates.

Transcription analysis of lignocellulolytic enzymes of Penicillium decumbens 114-2 and its catabolite-repression-resistant mutant

Penicillium decumbens 114-2 is a fast-growing filamentous fungus which secretes a variety of lignocellulolytic enzymes. Its catabolite-repression-resistant mutant JU-A10 with high secretion capacity of cellulolytic enzymes has been used industrially for biomass hydrolysis. Transcription levels of 6 important lignocellulolytic enzymes genes (cel5A, cel6A, cel7A, cel7B, xyn10A, and xyn11A) from both strains were determined on different carbon sources (glucose, sorbose, lactose, cellobiose, cellulose, and cellulose-wheat bran), by means of a real-time quantitative polymerase chain reaction. For both strains, the 6 genes are coordinately regulated at transcriptional level. Glucose and cellobiose repressed whereas cellulose and cellulose-wheat bran induced expression of 6 genes in both strains. Expression levels of all genes tested in the mutant strain JU-A10 were substantially higher than those in wild-type strain 114-2 on all carbon sources. On glucose repression condition, the mutant JU-A10 appeared obviously derepressed. Lactose was first proved to have an inductive effect on lignocellulolytic enzyme genes expression at lower concentration in Penicillium spp.

A specific, robust, and automated method for routine at-line monitoring of the concentration of cellulases in genetically modified sugarcane plants

Bagasse is one of the waste crop materials highlighted as commercially viable for cellulosic bio-ethanol production via enzymatic conversion to release fermentable sugars. Genetically modified sugarcane expressing cellobiohydrolases (CBH), endoglucanase (EG), and β-glucosidases (BG) provide a more cost-effective route to cellulose breakdown compared to culturing these enzymes in microbial tanks. Hence, process monitoring of the concentration profile of these key cellulases in incoming batches of sugarcane is required for fiscal measures and bio-ethanol process control. The existing methods due to their non-specificity, requirement of trained analysts, low sample throughput, and low amenability to automation are unsuitable for this purpose. Therefore, this paper explores a membrane-based sample preparation method coupled to capillary zone electrophoresis (CZE) to quantify these enzymes. The maximum enzyme extraction efficiency was obtained by using a polyethersulfone membrane with molecular cut-off of 10 kDa. The use of 15 mM, pH 7.75, phosphate buffer resulted in CZE separation and quantification of CBH, EG, and BG within 10 min. Migration time reproducibility was between 0.56% and 0.7% and hence, suitable for use with automatic peak detection software. Therefore, the developed CZE method is suitable for at-line analysis of BG, CBH, and EG in every batch of harvested sugarcane.

Characterization of the endoglucanase and glucomannanase activities of a glycoside hydrolase family 45 protein from Penicillium decumbens 114-2

The gene encoding a glycoside hydrolase (GH) family 45 endoglucanase (Cel45A) was cloned from P. decumbens 114-2 and expressed in Pichia pastoris. To our knowledge, this is the first report of characterization of a GH family 45 protein from Penicillium species. The purified recombinant enzyme showed a higher activity on konjac glucomannan (KGM) than on sodium carboxymethyl cellulose (CMC-Na) or phosphoric acid swollen cellulose (PASC). The highest hydrolytic activity was detected at pH5.0 on KGM and pH 3.5 on CMC-Na, indicating the mode of action on the two substrates may be different for Cel45A. The optimum temperatures on the two substrates were both 60 degrees C and about 90% relative activities were retained at 70 degrees C. Products released from PASC and CMC-Na were mainly cellobiose, cellotriose and cellotetraose. The protein with higher glucomannanase activity might help the efficient degradation of lignocellulose by P. decumbens in the natural state.

Cellulases from Penicillium funiculosum: production, properties and application to cellulose hydrolysis

The objective of this work is to investigate the utilization of two abundant agricultural residues in Brazil for the production and application of cellulolytic enzymes. Different materials obtained after pretreatment of sugarcane bagasse, as well as pure synthetic substrates, were considered for cellulase production by Penicillium funiculosum. The best results for FPase (354 U L(-1)) and beta-glucosidase (1,835 U L(-1)) production were observed when sugarcane bagasse partially delignified cellulignin (PDC) was used. The crude extract obtained from PDC fermentation was then partially characterized. Optimal temperatures for cellulase action ranged from 52 to 58 degrees C and pH values of around 4.9 contributed to maximum enzyme activity. At 37 degrees C, the cellulases were highly stable, losing less than 15% of their initial activity after 23 h of incubation. There was no detection of proteases in the P. funiculosum extract, but other hydrolases, such as endoxylanases, were identified (147 U L(-1)). Finally, when compared to commercial preparations, the cellulolytic complex from P. funiculosum showed more well-balanced amounts of beta-glucosidase, endo- and exoglucanase, resulting in the desired performance in the presence of a lignocellulosic material. Cellulases from this filamentous fungus had a higher glucose production rate (470 mg L(-1) h(-1)) when incubated with corn cob than with Celluclast, GC 220 and Spezyme (312, 454 and 400 mg L(-1) h(-1), respectively).

Enzymatic hydrolysis of steam-pretreated lignocellulosic materials with Trichoderma atroviride enzymes produced in-house

BACKGROUND

Improvement of the process of cellulase production and development of more efficient lignocellulose-degrading enzymes are necessary in order to reduce the cost of enzymes required in the biomass-to-bioethanol process.

RESULTS

Lignocellulolytic enzyme complexes were produced by the mutant Trichoderma atroviride TUB F-1663 on three different steam-pretreated lignocellulosic substrates, namely spruce, wheat straw and sugarcane bagasse. Filter paper activities of the enzymes produced on the three materials were very similar, while beta-glucosidase and hemicellulase activities were more dependent on the nature of the substrate. Hydrolysis of the enzyme preparations investigated produced similar glucose yields. However, the enzymes produced in-house proved to degrade the xylan and the xylose oligomers less efficiently than a commercial mixture of cellulase and beta-glucosidase. Furthermore, accumulation of xylose oligomers was observed when the TUB F-1663 supernatants were applied to xylan-containing substrates, probably due to the low beta-xylosidase activity of the enzymes. The efficiency of the enzymes produced in-house was enhanced by supplementation with extra commercial beta-glucosidase and beta-xylosidase. When the hydrolytic capacities of various mixtures of a commercial cellulase and a T. atroviride supernatant produced in the lab were investigated at the same enzyme loading, the glucose yield appeared to be correlated with the beta-glucosidase activity, while the xylose yield seemed to be correlated with the beta-xylosidase level in the mixtures.

CONCLUSION

Enzyme supernatants produced by the mutant T. atroviride TUB F-1663 on various pretreated lignocellulosic substrates have good filter paper activity values combined with high levels of beta-glucosidase activities, leading to cellulose conversion in the enzymatic hydrolysis that is as efficient as with a commercial cellulase mixture. On the other hand, in order to achieve good xylan conversion, the supernatants produced by the mutant have to be supplemented with additional beta-xylosidase activity.