Recombinant cellobiose dehydrogenase from Thermothelomyces thermophilus: Its functional characterization and applicability in cellobionic acid production

The fungus Thermothelomyces thermophilus is a thermotolerant microorganism that has been explored as a reservoir for enzymes (hydrolytic enzymes and oxidoreductases). The functional analysis of a recombinant cellobiose dehydrogenase (MtCDHB) from T. thermophilus demonstrated a thermophilic behavior, an optimal pH in alkaline conditions for inter-domain electron transfer, and catalytic activity on cellooligosaccharides with different degree of polymerization. Its applicability was evaluated to the sustainable production of cellobionic acid (CBA), a potential pharmaceutical and cosmetic ingredient rarely commercialized. Dissolving pulp was used as a disaccharide source for MtCDHB. Initially, recombinant exoglucanases (MtCBHI and MtCBHII) from T. thermophilus hydrolyzed the dissolving pulp, resulting in 87% cellobiose yield, which was subsequently converted into CBA by MtCDHB, achieving a 66% CBA yield after 24 h. These findings highlight the potential of MtCDHB as a novel approach to obtaining CBA through the bioconversion of a plant-based source.

Using low-shear aerated and agitated bioreactor for producing two specific laccases by trametes versicolor cultures induced by 2,5-xylidine: Process development and economic analysis

Laccase isoforms from basidiomycetes exhibit a superior redox potential compared to commercially available laccases obtained from ascomycete fungi, rendering them more reactive toward mono-substituted phenols and polyphenolic compounds. However, basidiomycetes present limitations for large-scale culture in liquid media, restraining the current availability of laccases from this fungal class. To advance laccase production from basidiomycetes, a newly designed 14-L low-shear aerated and agitated bioreactor provided enzyme titers up to 23.5 IU/mL from Trametes versicolor cultures. Produced enzymes underwent ultrafiltration and LC/MS-MS characterization, revealing the predominant production of only two out of the ten laccases predicted in the T. versicolor genome. Process simulation and economic analysis using SuperPro designer® suggested that T. versicolor laccase could be produced at US$ 3.60/kIU in a 200-L/batch enterprise with attractive economic parameters and a payback period of 1.7 years. The study indicates that new bioreactors with plain design help to produce low-cost enzymes from basidiomycetes.

A green pathway for lignin valorization: Enzymatic lignin depolymerization in biocompatible ionic liquids and deep eutectic solvents

Lignin depolymerization, which enables the breakdown of a complex and heterogeneous aromatic polymer into relatively uniform derivatives, serves as a critical process in valorization of lignin. Enzymatic lignin depolymerization has become a promising biological strategy to overcome the heterogeneity of lignin, due to its mild reaction conditions and high specificity. However, the low solubility of lignin compounds in aqueous environments prevents efficient lignin depolymerization by lignin-degrading enzymes. The employment of biocompatible ionic liquids (ILs) and deep eutectic solvents (DESs) in lignin fractionation has created a promising pathway to enzymatically depolymerize lignin within these green solvents to increase lignin solubility. In this review, recent research progress on enzymatic lignin depolymerization, particularly in a consolidated process involving ILs/DESs is summarized. In addition, the interactions between lignin-degrading enzymes and solvent systems are explored, and potential protein engineering methodology to improve the performance of lignin-degrading enzymes is discussed. Consolidation of enzymatic lignin depolymerization and biocompatible ILs/DESs paves a sustainable, efficient, and synergistic way to convert lignin into value-added products.

Analysis of Aureobasidium pullulans LB83 secretome reveals distinct carbohydrate active enzymes for biomass saccharification

Aureobasidium pullulans LB83 is a versatile biocatalyst that produces a plethora of bioactive products thriving on a variety of feedstocks under the varying culture conditions. In our last study using this microorganism, we found cellulase activity (FPase, 2.27 U/ml; CMCase, 7.42 U/ml) and other plant cell wall degrading enzyme activities grown on sugarcane bagasse and soybean meal as carbon source and nitrogen, respectively. In the present study, we provide insights on the secretome analysis of this enzymatic cocktail. The secretome analysis of A. pullulans LB83 by Liquid Chromatography coupled to Mass Spectroscopy (LC-MS/MS) revealed 38 classes of Carbohydrate Active enZymes (CAZymes) of a total of 464 identified proteins. These CAZymes consisted of 21 glycoside hydrolases (55.26%), 12 glycoside hydrolases harboring carbohydrate-binding module (31.58%), 4 carbohydrate esterases (10.53%) and one glycosyl transferase (2.63%). To the best of our knowledge, this is the first report on the secretome analysis of A. pullulans LB83.

Oxidative Machinery of basidiomycetes as potential enhancers in lignocellulosic biorefineries: A lytic polysaccharide monooxygenases approach

Basidiomycetes are renowned as highly effective decomposers of plant materials, due to their extensive array of oxidative enzymes, which enable them to efficiently break down complex lignocellulosic biomass structures. Among the oxidative machinery of industrially relevant basidiomycetes, the role of lytic polysaccharide monooxygenases (LPMO) in lignocellulosic biomass deconstruction is highlighted. So far, only a limited number of basidiomycetes LPMOs have been identified and heterologously expressed. These LPMOs have presented activity on cellulose and hemicellulose, as well as participation in the deconstruction of lignin. Expanding on this, the current review proposes both enzymatic and non-enzymatic mechanisms of LPMOs for biomass conversion, considering the significance of the Carbohydrate-Binding Modules and other C-terminal regions domains associated with their structure, which is involved in the deconstruction of lignocellulosic biomass.

Staphylococcus aureus microbial biofilms degradation using cellobiose dehydrogenase from Thermothelomyces thermophilus M77

This work reports biochemical characterization of Thermothelomyces thermophilus cellobiose dehydrogenase (TthCDHIIa) and its application as an antimicrobial and antibiofilm agent. We demonstrate that TthCDHIIa is thermostable in different ionic solutions and is capable of oxidizing multiple mono and oligosaccharide substrates and to continuously produce H2O2. Kinetics measurements depict the enzyme catalytic characteristics consistent with an Ascomycota class II CDH. Our structural analyses show that TthCDHIIa substrate binding pocket is spacious enough to accommodate larger cello and xylooligosaccharides. We also reveal that TthCDHIIa supplemented with cellobiose reduces the viability of S. aureus ATCC 25923 up to 32 % in a planktonic growth model and also inhibits its biofilm growth on 62.5 %. Furthermore, TthCDHIIa eradicates preformed S. aureus biofilms via H2O2 oxidative degradation of the biofilm matrix, making these bacteria considerably more susceptible to gentamicin and tetracycline.

Production of recombinant lytic polysaccharide monooxygenases and evaluation effect of its addition into Aspergillus fumigatus var. niveus cocktail for sugarcane bagasse saccharification

Lignocellulosic biomass is a promising alternative for producing biofuels, despite its recalcitrant nature. There are microorganisms in nature capable of efficiently degrade biomass, such as the filamentous fungi. Among them, Aspergillus fumigatus var. niveus (AFUMN) has a wide variety of carbohydrate-active enzymes (CAZymes), especially hydrolases, but a low number of oxidative enzymes in its genome. To confirm the enzymatic profile of this fungus, this study analyzed the secretome of AFUMN cultured in sugarcane bagasse as the sole carbon source. As expected, the secretome showed a predominance of hydrolytic enzymes compared to oxidative activity. However, it is known that hydrolytic enzymes act in synergy with oxidative proteins to efficiently degrade cellulose polymer, such as the Lytic Polysaccharide Monooxygenases (LPMOs). Thus, three LPMOs from the fungus Thermothelomyces thermophilus (TtLPMO9D, TtLPMO9H, and TtLPMO9O) were selected, heterologous expressed in Aspergillus nidulans, purified, and used to supplement the AFUMN secretome to evaluate their effect on the saccharification of sugarcane bagasse. The saccharification assay was carried out using different concentrations of AFUMN secretome supplemented with recombinant T. thermophilus LPMOs, as well as ascorbic acid as reducing agent for oxidative enzymes. Through a statistic design created by Design-Expert software, we were able to analyze a possible cooperative effect between these components. The results indicated that, in general, the addition of TtLPMO9D and ascorbic acid did not favor the conversion process in this study, while TtLPMO9O had a highly significant cooperative effect in bagasse saccharification compared to the control using only AFUMN secretome.

Endoglucanase effects on energy consumption in mechanical fibrillation of cellulose fibers into nanocelluloses

Enzymatic processing is seen as a promising means of moving toward environment-friendly industrial processes such as the use of endoglucanase (EG) enzyme in the production of nanocellulose. However, the properties that make EG pretreatment effective in the isolation of fibrillated cellulose remain a subject of debate. To address this issue, we considered EGs from four glycosyl hydrolase (GH) families (5, 6, 7 and 12) and investigated the roles of the tri-dimensional structures and catalytic features depending on the presence of a carbohydrate binding module (CBM). By using eucalyptus Kraft wood fibers, we produced cellulose nanofibrils (CNF) using mild enzymatic pretreatment followed by disc ultra-refining. Compared with the control (in the absence of pretreatment), the GH5 and GH12 enzymes (CBM free) reduced the fibrillation energy by approximately 15 %. The most efficient energy reduction, 25 and 32 %, was achieved with GH5 and GH6 linked to CBM, respectively. They improved the rheological properties of the CNF suspensions (noting that neither of these EGs released soluble products). Interestingly, while the hydrolytic activity was significant (released soluble products), GH7-CBM did not lead to a reduction in fibrillation energy. Hence, the large molecular weight and wide cleft of GH7-CBM led to soluble sugar release but contributed little to fibrillation. Our findings suggest that the improved fibrillation observed upon EG pretreatment is not a consequence of hydrolytic activity or release of products but mostly related to efficient adsorption on the substrate and modification of the surface viscoelastic (amorphogenesis).

Polymer ultrastructure governs AA9 lytic polysaccharide monooxygenases functionalization and deconstruction efficacy on cellulose nano-crystals

Lytic Polysaccharide MonoOxygenases display great variability towards cellulose ultrastructure while performing oxidative functionalization of the polymers. Aiming at employing AA9-LPMOs for isolation of cellulose nano-crystals (CNCs), the ratio between functionalization/crystalline degradation became a crucial parameter. Here are reported the constraints posed by the substrate ultrastructure on the activity of seven different AA9 LPMOs representative of various regioselectivity and substrate affinity: TtAA9E, TaAA9A, PcAA9D, MtAA9A, MtAA9D, MtAA9I-CBM and MtAA9J. The substrate crystallinity and dry matter loading greatly affected the seven AA9s in an enzyme-specific manner, impacting their efficiency for CNCs functionalization purposes. X-ray diffraction pattern analyses were used to assess the cracking efficacy of the enzymatic treatment to de-crystallize CNCs, revealing that those AA9s with minor efficiency in releasing oligosaccharides resulted instead the most disruptive towards the crystal lattice and in reducing the particle sizes. These non-catalytic effects were found comparable with the one caused by the expansin BsEXLX1 enzyme.

Exploring lignin depolymerization by a bi-enzyme system containing aryl alcohol oxidase and lignin peroxidase in aqueous biocompatible ionic liquids

Enzymatic depolymerization of lignin to produce low molecular weight products requires mild reaction conditions and exhibits higher selectivity compared to thermochemical lignin depolymerization. However, it remains challenging to depolymerize lignin enzymatically, partially due to the low solubility of lignin in aqueous phase. This study aimed to develop a novel approach to combine aqueous lignin extraction with enzymatic lignin depolymerization in biocompatible ionic liquids. A bi-enzyme system containing aryl alcohol oxidase (AAO) and lignin peroxidase (LiP) was developed to depolymerize lignin. Temperature and pH profiles for LiP and AAO were determined. Biocompatibilities of LiP and AAO in different deep eutectic solvents and ionic liquids were investigated. Aqueous cholinium glycinate was found to be an efficient and suitable solvent to solubilize lignin and serve as a biocompatible medium for enzymes to work. LiP and AAO together reduced lignin molecular weight in both solid and liquid phase after enzymatic lignin depolymerization.

Light-stimulated T. thermophilus two-domain LPMO9H: Low-resolution SAXS model and synergy with cellulases

Lytic polysaccharide monooxygenases (LPMOs), monocopper enzymes that oxidatively cleave recalcitrant polysaccharides, have important biotechnological applications. Thermothelomyces thermophilus is a rich source of biomass-active enzymes, including many members from auxiliary activities family 9 LPMOs. Here, we report biochemical and structural characterization of recombinant TtLPMO9H which oxidizes cellulose at the C1 and C4 positions and shows enhanced activity in light-driven catalysis assays. TtLPMO9H also shows activity against xyloglucan. The addition of TtLPMO9H to endoglucanases from four different glucoside hydrolase families (GH5, GH12, GH45 and GH7) revealed that the product formation was remarkably increased when TtLPMO9H was combined with GH7 endoglucanase. Finally, we determind the first low resolution small-angle X-ray scattering model of the two-domain TtLPMO9H in solution that shows relative positions of its two functional domains and a conformation of the linker peptide, which can be relevant for the catalytic oxidation of cellulose and xyloglucan.

Fed-batch production of Thermothelomyces thermophilus lignin peroxidase using a recombinant Aspergillus nidulans strain in stirred-tank bioreactor

Enzymatic lignin depolymerization is considered a favorable approach to utilize lignin due to the higher selectivity and less energy requirement when compared to thermochemical lignin valorization. Lignin peroxidase (LiP) is one of the key enzymes involved in lignin degradation and possesses high redox potential to oxidize non-phenolic structures and phenolic compounds in lignin. However, the production of LiP is mainly from white-rot fungi at small scales. It is critical to discover new LiP from other microorganisms and produce LiP at large scales. This study aims to produce a novel LiP originally from Thermothelomyces thermophiles using a recombinant Aspergillus nidulans strain. The LiP production medium was optimized, and different fed-batch strategies for LiP production were investigated to improve LiP activity, yield, and productivity. Results demonstrated that LiP production was enhanced by using multi-pulse fed-batch fermentation. A maximum LiP activity of 1,645 mU/L with a protein concentration of 0.26 g/L was achieved.

Comparative analysis of two recombinant LPMOs from Aspergillus fumigatus and their effects on sugarcane bagasse saccharification

Lytic polysaccharide monooxygenases (LPMOs) have been introduced into industrial cocktails used for biomass saccharification due to their capacity to boost enzymatic conversion of recalcitrant cellulose. The genome of the thermotolerant ascomycete Aspergillus fumigatus encodes 7 genes for LPMOs that belong to auxiliary activity family 9 (AA9). Here, we cloned, successfully expressed and performed biochemical evaluation of two CBM-less A. fumigatus LPMOs (AfAA9A and AfAA9B). A high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) analysis demonstrated that AfAA9A and AfAA9B are able to oxide cellulose at C1 and C1/C4 positions, respectively. Synergic effects of LPMOs (separately and in combination) with cellulases were investigated. Supplementation of Celluclast 1.5 L with a low concentration of AfAA9B improved in 20 % the saccharification of sugarcane bagasse pretreated by steam explosion (SEB), while AfAA9A did not improvethe saccharification. Analysis of the hydrolyzed biomass by confocal laser scanning microscopy (CLSM) showed the LPMOs are promoting lignin oxidation in the lignocellulosic material. This study complements the available results concerning the utilization of LPMOs in the enzymatic saccharification of lignocellulosic biomass.

Functional characterization of a novel thermophilic exo-arabinanase from Thermothielavioides terrestris

Arabinanases from glycoside hydrolase family GH93 are enzymes with exo-activity that hydrolyze the α-1,5 bonds between arabinose residues present on arabinan. Currently, several initiatives aiming to use byproducts rich in arabinan such as pectin and sugar beet pulp as raw material to produce various compounds of interest are being developed. However, it is necessary to use robust enzymes that have an optimal performance under pH and temperature conditions used in the industrial processes. In this work, the first GH93 from the thermophilic fungus Thermothielavioides terrestris (Abn93T) was heterologously expressed in Aspergillus nidulans, purified and biochemically characterized. The enzyme is a thermophilic glycoprotein (optimum activity at 70 °C) with prolonged stability in acid pHs (4.0 to 6.5). The presence of glycosylation affected slightly the hydrolytic capacity of the enzyme, which was further increased by 34% in the presence of 1 mM CoCl₂. Small-angle X-ray scattering results show that Abn93T is a globular-like-shaped protein with a slight bulge at one end. The hydrolytic mechanism of the enzyme was elucidated using capillary zone electrophoresis and molecular docking calculations. Abn93T has an ability to produce (in synergism with arabinofuranosidases) arabinose and arabinobiose from sugar beet arabinan, which can be explored as fermentable sugars and prebiotics. KEY POINTS: • Thermophilic exo-arabinanase from family GH93 • Molecular basis of arabinan depolymerization.

Production of cellulases by Aureobasidium pullulans LB83: optimization, characterization, and hydrolytic potential for the production of cellulosic sugars

Aureobasidium pullulans LB83 was evaluated for cellulase production under submerged fermentation conditions. Different process variables such as carbon sources (corn cob, sugarcane bagasse, and sugarcane straw), synthetic (urea, ammonium sulfate, and peptone), and non-synthetic (soybean meal, rice, and corn meal) nitrogen sources and inoculum size were evaluated by one parameter at-a-time strategy. Aureobasidium pullulans LB83 showed maximum cellulase activity (FPase, 2.27 U/mL; CMCase, 7.42 U/mL) on sugarcane bagasse. Among the nitrogen sources, soybean meal as a non-synthetic nitrogen sources showed a maximum cellulase activity (FPase 2.45 U/mL; CMCase, 6.86 U/mL) after 60 hr. The inoculum size of 1.6 × 106 CFU/mL had the maximum FPase and CMCase activities of 3.14 and 8.74 U/mL, respectively. For the enzymatic hydrolysis, both the commercial cellulase (10 FPU/g of Cellic CTec 2 (#A) and 10 FPU/g of crude enzyme extract (CEE) (#B), and varying ratio of CTec 2 and CEE in combination #C (5 FPU/g of CTec 2 + 5 FPU/g CEE), combination #D (2.5 FPU/g of CTec 2 + 7.5 FPU/g CEE), and combination #E (7.5 FPU/g of CTec 2 + 2.5 FPU/g CEE) were assessed for enzymatic hydrolysis of delignified sugarcane bagasse. Enzyme combination #C showed maximum hydrolysis yield of 92.40%. The study shows the hydrolytic potential of cellulolytic enzymes from A. pullulans LB83 for lignocellulosic sugars production from delignified sugarcane bagasse.

The Secretome of Phanerochaete chrysosporium and Trametes versicolor Grown in Microcrystalline Cellulose and Use of the Enzymes for Hydrolysis of Lignocellulosic Materials

The ability of white-rot fungi to degrade polysaccharides in lignified plant cell walls makes them a suitable reservoir for CAZyme prospects. However, to date, CAZymes from these species are barely studied, which limits their use in the set of choices for biomass conversion in modern biorefineries. The current work joined secretome studies of two representative white-rot fungi, Phanerochaete chrysosporium and Trametes versicolor, with expression analysis of cellobiohydrolase (CBH) genes, and use of the secretomes to evaluate enzymatic conversion of simple and complex sugarcane-derived substrates. Avicel was used to induce secretion of high levels of CBHs in the extracellular medium. A total of 56 and 58 proteins were identified in cultures of P. chrysosporium and T. versicolor, respectively, with 78-86% of these proteins corresponding to plant cell wall degrading enzymes (cellulolytic, hemicellulolytic, pectinolytic, esterase, and auxiliary activity). CBHI predominated among the plant cell wall degrading enzymes, corresponding to 47 and 34% of the detected proteins in P. chrysosporium and T. versicolor, respectively, which confirms that Avicel is an efficient CBH inducer in white-rot fungi. The induction by Avicel of genes encoding CBHs (cel) was supported by high expression levels of cel7D and cel7C in P. chrysosporium and T. versicolor, respectively. Both white-rot fungi secretomes enabled hydrolysis experiments at 10 FPU/g substrate, despite the varied proportions of CBHs and other enzymes present in each case. When low recalcitrance sugarcane pith was used as a substrate, P. chrysosporium and T. versicolor secretomes performed similarly to Cellic® CTec2. However, the white-rot fungi secretomes were less efficient than Cellic® CTec2 during hydrolysis of more recalcitrant substrates, such as acid or alkaline sulfite-pretreated sugarcane bagasse, likely because Cellic® CTec2 contains an excess of CBHs compared with the white-rot fungi secretomes. General comparison of the white-rot fungi secretomes highlighted T. versicolor enzymes for providing high glucan conversions, even at lower proportion of CBHs, probably because the other enzymes present in this secretome and CBHs lacking carbohydrate-binding modules compensate for problems associated with unproductive binding to lignin.

Optimization of process parameters and fermentation strategy for xylanase production in a stirred tank reactor using a mutant Aspergillus nidulans strain

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In batch fermentation, xylanase productivity was 313 U/mL/day.

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Maximum xylanase productivity was achieved at aeration of 2 vvm and 400 rpm.

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The optimum kLa for an efficient xylanase production was found to be 38.5 h⁻¹.

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Repeated batch fermentation increased xylanase productivity to 373 U/mL/day.

The present work studied the optimization of aeration rate, agitation rate and oxygen transfer and the use of various batch fermentation strategies for xylanase production from a recombinant Aspergillus nidulans strain in a 3 L stirred tank reactor. Maximum xylanase production of 1250 U/mL with productivity of 313 U/mL/day was obtained under an aeration rate of 2 vvm and an agitation rate of 400 rpm using batch fermentation. The optimum volumetric oxygen transfer coefficient (k_La) for efficient xylanase production was found to be 38.6 h⁻¹. Fed batch mode and repeated batch fermentation was also performed with k_La was 38.6 h⁻¹. Xylanase enzyme productivity increased to 327 with fed batch fermentation and 373 U/mL/day with repeated batch fermentation. Also, maximum xylanase activity increased to 1410 U/mL with fed batch fermentation and 1572 U/mL with repeated batch fermentation.

Heterologous expression and functional characterization of a GH10 endoxylanase from Aspergillus fumigatus var. niveus with potential biotechnological application

Xylanases decrease the xylan content in pretreated biomass releasing it from hemicellulose, thus improving the accessibility of cellulose for cellulases. In this work, an endo-β-1,4-xylanase from Aspergillus fumigatus var. niveus (AFUMN-GH10) was successfully expressed. The structural analysis and biochemical characterization showed this AFUMN-GH10 does not contain a carbohydrate-binding module. The enzyme retained its activity in a pH range from 4.5 to 7.0, with an optimal temperature at 60 °C. AFUMN-GH10 showed the highest activity in beechwood xylan. The mode of action of AFUMN-GH10 was investigated by hydrolysis of APTS-labeled xylohexaose, which resulted in xylotriose and xylobiose as the main products. AFUMN-GH10 released 27% of residual xylan from hydrothermally-pretreated corn stover and 14% of residual xylan from hydrothermally-pretreated sugarcane bagasse. The results showed that environmentally friendly pretreatment followed by enzymatic hydrolysis with AFUMN-GH10 in low concentration is a suitable method to remove part of residual and recalcitrant hemicellulose from biomass.

The secretome of two representative lignocellulose-decay basidiomycetes growing on sugarcane bagasse solid-state cultures

Secretome evaluations of lignocellulose-decay basidiomycetes can reveal new enzymes in selected fungal species that degrade specific substrates. Proteins discovered in such studies can support biorefinery development. Brown-rot (Gloeophyllum trabeum) and white-rot (Pleurotus ostreatus) fungi growing in sugarcane bagasse solid-state cultures produced 119 and 63 different extracellular proteins, respectively. Several of the identified enzymes are suitable for in vitro biomass conversion, including a range of cellulases (endoglucanases, cellobiohydrolases and β-glucosidases), hemicellulases (endoxylanases, α-arabinofuranosidases, α-glucuronidases and acetylxylan esterases) and carbohydrate-active auxiliary proteins, such as AA9 lytic polysaccharide monooxygenase, AA1 laccase and AA2 versatile peroxidase. Extracellular oxalate decarboxylase was also detected in both fungal species, exclusively in media containing sugarcane bagasse. Interestingly, intracellular AA6 quinone oxidoreductases were also exclusively produced under sugarcane bagasse induction in both fungi. These enzymes promote quinone redox cycling, which is used to produce Fenton's reagents by lignocellulose-decay fungi. Hitherto undiscovered hypothetical proteins that are predicted in lignocellulose-decay fungi genomes appeared in high relative abundance in the cultures containing sugarcane bagasse, which suggests undisclosed, new biochemical mechanisms that are used by lignocellulose-decay fungi to degrade sugarcane biomass. In general, lignocellulose-decay fungi produce a number of canonical hydrolases, as well as some newly observed enzymes, that are suitable for in vitro biomass digestion in a biorefinery context.

Terbinafine resistance conferred by multiple copies of the salicylate 1-monooxygenase gene in Trichophyton rubrum

Resistance to antifungals is a leading concern in the treatment of human mycoses. We demonstrate that the salA gene, encoding salicylate 1-monooxygenase, is involved in resistance of the dermatophyte Trichophyton rubrum to terbinafine, one of the most effective antifungal drugs against dermatophytes. A strain with multiple copies of salA was constructed and exhibited elevated expression of salA and increased terbinafine resistance. This reflects a mechanism not yet reported in a pathogenic fungus.

Feruloyl esterases: Biocatalysts to overcome biomass recalcitrance and for the production of bioactive compounds

Ferulic acid and its hydroxycinnamate derivatives represent one of the most abundant forms of low molecular weight phenolic compounds in plant biomass. Feruloyl esterases are part of a microorganism's plant cell wall-degrading enzymatic arsenal responsible for cleaving insoluble wall-bound hydroxycinnamates and soluble cytosolic conjugates. Stimulated by industrial requirements, accelerating scientific discoveries and knowledge transfer, continuous improvement efforts have been made to identify, create and repurposed biocatalysts dedicated to plant biomass conversion and biosynthesis of high-added value molecules. Here we review the basic knowledge and recent advances in biotechnological characteristics and the gene content encoding for feruloyl esterases. Information about several enzymes is systematically organized according to their function, biochemical properties, substrate specificity, and biotechnological applications. This review contributes to further structural, functional, and biotechnological R&D both for obtaining hydroxycinnamates from agricultural by-products as well as for lignocellulose biomass treatments aiming for production of bioethanol and other derivatives of industrial interest.

The Genome of a Thermo Tolerant, Pathogenic Albino Aspergillus fumigatus

Biotechnologists are interested in thermo tolerant fungi to manufacture enzymes active and stable at high temperatures, because they provide improved catalytic efficiency, strengthen enzyme substrate interactions, accelerate substrate enzyme conversion rates, enhance mass transfer, lower substrate viscosity, lessen contamination risk and offer the potential for enzyme recycling. Members of the genus Aspergillus live a wide variety of lifestyles, some embrace GRAS status routinely employed in food processing while others such as Aspergillus fumigatus are human pathogens. A. fumigatus produces melanins, pyomelanin protects the fungus against reactive oxygen species and DHN melanin produced by the pksP gene cluster confers the gray-greenish color. pksP mutants are attenuated in virulence. Here we report on the genomic DNA sequence of a thermo tolerant albino Aspergillus isolated from rain forest composted floors. Unexpectedly, the nucleotide sequence was 95.7% identical to the reported by Aspergillus fumigatus Af293. Genome size and predicted gene models were also highly similar, however differences in DNA content and conservation were observed. The albino strain, classified as Aspergillus fumigatus var. niveus, had 160 gene models not present in A. fumigatus Af293 and A. fumigatus Af293 had 647 not found in the albino strain. Furthermore, the major pigment generating gene cluster pksP appeared to have undergone genomic rearrangements and a key tyrosinase present in many aspergilli was missing from the genome. Remarkably however, despite the lack of pigmentation A. fumigatus var. niveus killed neutropenic mice and survived macrophage engulfment at similar rates as A. fumigatus Af293.

Cloning, heterologous expression and biochemical characterization of a non-specific endoglucanase family 12 from Aspergillus terreus NIH2624

The cellulases from Glycoside Hydrolyses family 12 (GH12) play an important role in cellulose degradation and plant cell wall deconstruction being widely used in a number of bioindustrial processes. Aiming to contribute toward better comprehension of these class of the enzymes, here we describe a high-yield secretion of a endoglucanase GH12 from Aspegillus terreus (AtGH12), which was cloned and expressed in Aspergillus nidulans strain A773. The purified protein was used for complete biochemical and functional characterization. The optimal temperature and pH of the enzyme were 55°C and 5.0 respectively, which has high activity against β-glucan and xyloglucan and also is active toward glucomannan and CMC. The enzyme retained activity up to 60°C. AtGH12 is strongly inhibited by Cu²⁺, Fe²⁺, Cd²⁺, Mn²⁺, Ca²⁺, Zn²⁺ and EDTA, whereas K⁺, Tween, Cs⁺, DMSO, Triton X-100 and Mg²⁺ enhanced the enzyme activity. Furthermore, SAXS data reveal that the enzyme has a globular shape and CD analysis demonstrated a prevalence of a β-strand structure corroborating with typical β-sheets fold commonly found for other endoglucanases from GH12 family.

Xyloglucan breakdown by endo-xyloglucanase family 74 from Aspergillus fumigatus

Xyloglucan is the most abundant hemicellulose in primary walls of spermatophytes except for grasses. Xyloglucan-degrading enzymes are important in lignocellulosic biomass hydrolysis because they remove xyloglucan, which is abundant in monocot-derived biomass. Fungal genomes encode numerous xyloglucanase genes, belonging to at least six glycoside hydrolase (GH) families. GH74 endo-xyloglucanases cleave xyloglucan backbones with unsubstituted glucose at the -1 subsite or prefer xylosyl-substituted residues in the -1 subsite. In this work, 137 GH74-related genes were detected by examining 293 Eurotiomycete genomes and Ascomycete fungi contained one or no GH74 xyloglucanase gene per genome. Another interesting feature is that the triad of tryptophan residues along the catalytic cleft was found to be widely conserved among Ascomycetes. The GH74 from Aspergillus fumigatus (AfXEG74) was chosen as an example to conduct comprehensive biochemical studies to determine the catalytic mechanism. AfXEG74 has no CBM and cleaves the xyloglucan backbone between the unsubstituted glucose and xylose-substituted glucose at specific positions, along the XX motif when linked to regions deprived of galactosyl branches. It resembles an endo-processive activity, which after initial random hydrolysis releases xyloglucan-oligosaccharides as major reaction products. This work provides insights on phylogenetic diversity and catalytic mechanism of GH74 xyloglucanases from Ascomycete fungi.

ANTIFUNGAL SUSCEPTIBILITY TESTING AND GENOTYPING CHARACTERIZATION OF Cryptococcus neoformans AND gattii ISOLATES FROM HIV-INFECTED PATIENTS OF RIBEIRÃO PRETO, SÃO PAULO, BRAZIL

Cryptococcosis is a leading invasive fungal infection in immunocompromised patients. Considering the high prevalence and severity of these infections in immunocompromised patients attended at HC-FMRP-USP, the present research aimed to characterize the clinical isolates of Cryptococcus strains by biochemical and molecular methods and evaluate antifungal susceptibility of clinical isolates. Fifty isolates from 32 HIV-positive patients were obtained at HC-FMRP-USP. Most of the isolates (78.1%) were identified as C. neoformans, and 100% of C. neoformans and C. gattii strains were susceptible to amphotericin B, ketoconazole and fluconazole. All isolates were classified as serotype A (grubbii variety) by PCR and most of them were characterized in mating type MATa. PCR analysis of specific M13 microsatellite sequence revealed that VNI type was predominant among C. neoformans, while VGII was predominant among C. gattii. The strains did not show a significant resistance to the antifungals tested, and Canavanine-Glycine-Bromthymol Blue Agar (CGB) proved to be a reliable test presenting a good correlation with the molecular characterization. C. neoformans isolated from disseminated infections in the same patient showed molecular identity when different anatomical sites were compared; besides, the studied strains did not present a significant increase in resistance to antifungal agents. In addition, the homogeneity of the molecular types and detection of the mating types suggested a low possibility of crossing among the strains.

The functional properties of a xyloglucanase (GH12) of Aspergillus terreus expressed in Aspergillus nidulans may increase performance of biomass degradation

Filamentous fungi are attractive hosts for heterologous protein expression due to their capacity to secrete large amounts of enzymes into the extracellular medium. Xyloglucanases, which specifically hydrolyze xyloglucan, have been recently applied in lignocellulosic biomass degradation and conversion in many other industrial processes. In this context, this work aimed to clone, express, and determine the functional properties of a recombinant xyloglucanase (AtXEG12) from Aspergillus terreus, and also its solid-state (SSF) and submerged (SmF) fermentation in bioreactors. The purified AtXEG12 showed optimum pH and temperature of 5.5 and 65 °C, respectively, demonstrating to be 90 % stable after 24 h of incubation at 50 °C. AtXEG12 activity increased in the presence of 2-mercaptoethanol (65 %) and Zn⁺² (45 %), while Cu⁺² and Ag⁺ ions drastically decreased its activity. A substrate assay showed, for the first time for this enzyme's family, xylanase activity. The enzyme exhibited high specificity for tamarind xyloglucan (K _M 1.2 mg mL^-1) and V _max of 17.4 μmol min^-1 mg^-1 of protein. The capillary zone electrophoresis analysis revealed that AtXEG12 is an endo-xyloglucanase. The heterologous xyloglucanase secretion was greater than the production by wild-type A. terreus cultivated in SmF. On the other hand, AtXEG12 activity reached by SSF was sevenfold higher than values achieved by SmF, showing that the expression of recombinant enzymes can be significantly improved by cultivation under SSF.

Exploring glycoside hydrolases and accessory proteins from wood decay fungi to enhance sugarcane bagasse saccharification

BACKGROUND

Glycoside hydrolases (GHs) and accessory proteins are key components for efficient and cost-effective enzymatic hydrolysis of polysaccharides in modern, biochemically based biorefineries. Currently, commercialized GHs and accessory proteins are produced by ascomycetes. However, the role of wood decay basidiomycetes proteins in biomass saccharification has not been extensively pursued. Wood decay fungi degrade polysaccharides in highly lignified tissues in natural environments, and are a promising enzyme source for improving enzymatic cocktails that are designed for in vitro lignocellulose conversion.

RESULTS

GHs and accessory proteins were produced by representative brown- and white-rot fungi, Laetiporus sulphureus and Pleurotus ostreatus, respectively. Concentrated protein extracts were then used to amend commercial enzymatic cocktails for saccharification of alkaline-sulfite pretreated sugarcane bagasse. The main enzymatic activities found in the wood decay fungal protein extracts were attributed to endoglucanases, xylanases and β-glucosidases. Cellobiohydrolase (CBH) activities in the L. sulphureus and P. ostreatus extracts were low and nonexistent, respectively. The initial glucan conversion rates were boosted when the wood decay fungal proteins were used to replace half of the enzymes from the commercial cocktails. L. sulphureus proteins increased the glucan conversion levels, with values above those observed for the full load of commercial enzymes. Wood decay fungal proteins also enhanced the xylan conversion efficiency due to their high xylanase activities. Proteomic studies revealed 104 and 45 different proteins in the P. ostreatus and L. sulphureus extracts, respectively. The enhancement of the saccharification of alkaline-pretreated substrates by the modified enzymatic cocktails was attributed to the following protein families: GH5- and GH45-endoglucanases, GH3-β-glucosidases, and GH10-xylanases.

CONCLUSIONS

The extracellular proteins produced by wood decay fungi provide useful tools to improve commercial enzyme cocktails that are currently used for the saccharification of alkaline-pretreated lignocellulosic substrates. The relevant proteins encompass multiple glycoside hydrolase families, including the GH5- and GH45-endoglucanases, GH3-β-glucosidases, and GH10-xylanases.

Co-cultivation of Aspergillus nidulans Recombinant Strains Produces an Enzymatic Cocktail as Alternative to Alkaline Sugarcane Bagasse Pretreatment

Plant materials represent a strategic energy source because they can give rise to sustainable biofuels through the fermentation of their carbohydrates. A clear example of a plant-derived biofuel resource is the sugar cane bagasse exhibiting 60-80% of fermentable sugars in its composition. However, the current methods of plant bioconversion employ severe and harmful chemical/physical pretreatments raising biofuel cost production and environmental degradation. Replacing these methods with co-cultivated enzymatic cocktails is an alternative. Here we propose a pretreatment for sugarcane bagasse using a multi-enzymatic cocktail from the co-cultivation of four Aspergillus nidulans recombinant strains. The co-cultivation resulted in the simultaneous production of GH51 arabinofuranosidase (AbfA), GH11 endo-1,4-xylanase (XlnA), GH43 endo-1,5-arabinanase (AbnA) and GH12 xyloglucan specific endo-β-1,4-glucanase (XegA). This core set of recombinant enzymes was more efficient than the alternative alkaline method in maintaining the cellulose integrity and exposing this cellulose to the following saccharification process. Thermogravimetric and differential thermal analysis revealed residual byproducts on the alkali pretreated biomass, which were not found in the enzymatic pretreatment. Therefore, the enzymatic pretreatment was residue-free and seemed to be more efficient than the applied alkaline method, which makes it suitable for bioethanol production.

Continuous xylanase production with Aspergillus nidulans under pyridoxine limitation using a trickle bed reactor

A trickle bed reactor (TBR) with recycle was designed and tested using Aspergillus nidulans with a pyridoxine marker and over-expressing/secreting recombinant client xylanase B (XynB). The pyridoxine marker prevented the fungus from synthesizing its own pyridoxine and fungus was unable to grow when no pyridoxine was present in the medium; however, enzyme production was unaffected. Uncontrolled mycelia growth that led to clogging of the TBR was observed when fungus without a pyridoxine marker was used for XynB production. Using the fungus with pyridoxine marker, the TBR was operated continuously for 18 days and achieved a XynB output of 41 U/ml with an influent and effluent flow rate of 0.5 ml/min and a recycle flow rate of 56 ml/min. Production yields in the TBR were 1.4 times greater than a static tray culture and between 1.1 and 67 times greater than yields for SSF enzyme production stated in the literature.

Understanding the function of conserved variations in the catalytic loops of fungal glycoside hydrolase family 12

Enzymes that cleave the xyloglucan backbone at unbranched glucose residues have been identified in GH families 5, 7, 12, 16, 44, and 74. Fungi produce enzymes that populate 20 of 22 families that are considered critical for plant biomass deconstruction. We searched for GH12-encoding genes in 27 Eurotiomycetes genomes. After analyzing 50 GH12-related sequences, the conserved variations of the amino acid sequences were examined. Compared to the endoglucanases, the endo-xyloglucanase-associated YSG deletion at the negative subsites of the catalytic cleft with a SST insertion at the reducing end of the substrate-binding crevice is highly conserved. In addition, a highly conserved alanine residue was identified in all xyloglucan-specific enzymes, and this residue is substituted by arginine in more promiscuous glucanases. To understand the basis for the xyloglucan specificity displayed by certain GH12 enzymes, two fungal GH12 endoglucanases were chosen for mutagenesis and functional studies: an endo-xyloglucanase from Aspergillus clavatus (AclaXegA) and an endoglucanase from A. terreus (AtEglD). Comprehensive molecular docking studies and biochemical analyses were performed, revealing that mutations at the entrance of the catalytic cleft in AtEglD result in a wider binding cleft and the alteration of the substrate-cleavage pattern, implying that a trio of residues coordinates the interactions and binding to linear glycans. The loop insertion at the crevice-reducing end of AclaXegA is critical for catalytic efficiency to hydrolyze xyloglucan. The understanding of the structural elements governing endo-xyloglucanase activity on linear and branched glucans will facilitate future enzyme modifications with potential applications in industrial biotechnology.

Expression, purification, crystallization and preliminary X-ray diffraction analysis of Aspergillus terreus endo-β-1,4-glucanase from glycoside hydrolase family 12

Endoglucanases are important enzymes that are involved in the modification and degradation of cellulose. Filamentous fungi such as Aspergillus terreus are effective biomass degraders in nature owing to their capacity to produce an enzymatic arsenal of glycoside hydrolases, including endoglucanase from glycoside hydrolase family 12 (GH12). The A. terreus GH12 endoglucanase was cloned and overexpressed in A. nidulans, purified and crystallized. A single crystal was obtained from a solution consisting of 2 M ammonium sulfate, 5%(v/v) 2-propanol. X-ray diffraction data were collected to a resolution of 1.85 Å using synchrotron radiation and a preliminary molecular-replacement solution was obtained in the trigonal space group P3(2)21. The unit-cell parameters were a = b = 103.24, c = 48.96 Å.

Biomass-to-bio-products application of feruloyl esterase from Aspergillus clavatus

The structural polysaccharides contained in plant cell walls have been pointed to as a promising renewable alternative to petroleum and natural gas. Ferulic acid is a ubiquitous component of plant polysaccharides, which is found in either monomeric or dimeric forms and is covalently linked to arabinosyl residues. Ferulic acid has several commercial applications in food and pharmaceutical industries. The study herein introduces a novel feruloyl esterase from Aspergillus clavatus (AcFAE). Along with a comprehensive functional and biophysical characterization, the low-resolution structure of this enzyme was also determined by small-angle X-ray scattering. In addition, we described the production of phenolic compounds with antioxidant capacity from wheat arabinoxylan and sugarcane bagasse using AcFAE. The ability to specifically cleave ester linkages in hemicellulose is useful in several biotechnological applications, including improved accessibility to lignocellulosic enzymes for biofuel production.

Functional characterization and synergic action of fungal xylanase and arabinofuranosidase for production of xylooligosaccharides

Plant cell wall degrading enzymes are key technological components in biomass bioconversion platforms for lignocellulosic materials transformation. Cost effective production of enzymes and identification of efficient degradation routes are two economic bottlenecks that currently limit the use of renewable feedstocks through an environmental friendly pathway. The present study describes the hypersecretion of an endo-xylanase (GH11) and an arabinofuranosidase (GH54) by a fungal expression system with potential biotechnological application, along with comprehensive characterization of both enzymes, including spectrometric analysis of thermal denaturation, biochemical characterization and mode of action description. The synergistic effect of these enzymes on natural substrates such as sugarcane bagasse, demonstrated the biotechnological potential of using GH11 and GH54 for production of probiotic xylooligosaccharides from plant biomass. Our findings shed light on enzymatic mechanisms for xylooligosaccharide production, as well as provide basis for further studies for the development of novel enzymatic routes for use in biomass-to-bioethanol applications.

High-yield secretion of multiple client proteins in Aspergillus

Production of pure and high-yield client proteins is an important technology that addresses the need for industrial applications of enzymes as well as scientific experiments in protein chemistry and crystallization. Fungi are utilized in industrial protein production because of their ability to secrete large quantities of proteins. In this study, we engineered a high-expression-secretion vector, pEXPYR that directs proteins towards the extracellular medium in two Aspergillii host strains, examine the effect of maltose-induced over-expression and protein secretion as well as time and pH-dependent protein stability in the medium. We describe five client proteins representing a core set of hemicellulose degrading enzymes that accumulated up to 50-100 mg/L of protein. Using a recyclable genetic marker that allows serial insertion of multiple genes, simultaneous hyper-secretion of three client proteins in a single host strain was accomplished.

Two structurally discrete GH7-cellobiohydrolases compete for the same cellulosic substrate fiber

BACKGROUND

Cellulose consisting of arrays of linear beta-1,4 linked glucans, is the most abundant carbon-containing polymer present in biomass. Recalcitrance of crystalline cellulose towards enzymatic degradation is widely reported and is the result of intra- and inter-molecular hydrogen bonds within and among the linear glucans. Cellobiohydrolases are enzymes that attack crystalline cellulose. Here we report on two forms of glycosyl hydrolase family 7 cellobiohydrolases common to all Aspergillii that attack Avicel, cotton cellulose and other forms of crystalline cellulose.

RESULTS

Cellobiohydrolases Cbh1 and CelD have similar catalytic domains but only Cbh1 contains a carbohydrate-binding domain (CBD) that binds to cellulose. Structural superpositioning of Cbh1 and CelD on the Talaromyces emersonii Cel7A 3-dimensional structure, identifies the typical tunnel-like catalytic active site while Cbh1 shows an additional loop that partially obstructs the substrate-fitting channel. CelD does not have a CBD and shows a four amino acid residue deletion on the tunnel-obstructing loop providing a continuous opening in the absence of a CBD. Cbh1 and CelD are catalytically functional and while specific activity against Avicel is 7.7 and 0.5 U.mg prot-1, respectively specific activity on pNPC is virtually identical. Cbh1 is slightly more stable to thermal inactivation compared to CelD and is much less sensitive to glucose inhibition suggesting that an open tunnel configuration, or absence of a CBD, alters the way the catalytic domain interacts with the substrate. Cbh1 and CelD enzyme mixtures on crystalline cellulosic substrates show a strong combinatorial effort response for mixtures where Cbh1 is present in 2:1 or 4:1 molar excess. When CelD was overrepresented the combinatorial effort could only be partially overcome. CelD appears to bind and hydrolyze only loose cellulosic chains while Cbh1 is capable of opening new cellulosic substrate molecules away from the cellulosic fiber.

CONCLUSION

Cellobiohydrolases both with and without a CBD occur in most fungal genomes where both enzymes are secreted, and likely participate in cellulose degradation. The fact that only Cbh1 binds to the substrate and in combination with CelD exhibits strong synergy only when Cbh1 is present in excess, suggests that Cbh1 unties enough chains from cellulose fibers, thus enabling processive access of CelD.

Functional characterization and oligomerization of a recombinant xyloglucan-specific endo-β-1,4-glucanase (GH12) from Aspergillus niveus

Xyloglucan is a major structural polysaccharide of the primary (growing) cell wall of higher plants. It consists of a cellulosic backbone (beta-1,4-linked glucosyl residues) that is frequently substituted with side chains. This report describes Aspergillus nidulans strain A773 recombinant secretion of a dimeric xyloglucan-specific endo-β-1,4-glucanohydrolase (XegA) cloned from Aspergillus niveus. The ORF of the A. niveus xegA gene is comprised of 714 nucleotides, and encodes a 238 amino acid protein with a calculated molecular weight of 23.5kDa and isoelectric point of 4.38. The optimal pH and temperature were 6.0 and 60°C, respectively. XegA generated a xyloglucan-oligosaccharides (XGOs) pattern similar to that observed for cellulases from family GH12, i.e., demonstrating that its mode of action includes hydrolysis of the glycosidic linkages between glucosyl residues that are not branched with xylose. In contrast to commercial lichenase, mixed linkage beta-glucan (lichenan) was not digested by XegA, indicating that the enzyme did not cleave glucan β-1,3 or β-1,6 bonds. The far-UV CD spectrum of the purified enzyme indicated a protein rich in β-sheet structures as expected for GH12 xyloglucanases. Thermal unfolding studies displayed two transitions with mid-point temperatures of 51.3°C and 81.3°C respectively, and dynamic light scattering studies indicated that the first transition involves a change in oligomeric state from a dimeric to a monomeric form. Since the enzyme is a predominantly a monomer at 60°C, the enzymatic assays demonstrated that XegA is more active in its monomeric state.

Transcriptional profiling reveals the expression of novel genes in response to various stimuli in the human dermatophyte Trichophyton rubrum

Background

Cutaneous mycoses are common human infections among healthy and immunocompromised hosts, and the anthropophilic fungus Trichophyton rubrum is the most prevalent microorganism isolated from such clinical cases worldwide. The aim of this study was to determine the transcriptional profile of T. rubrum exposed to various stimuli in order to obtain insights into the responses of this pathogen to different environmental challenges. Therefore, we generated an expressed sequence tag (EST) collection by constructing one cDNA library and nine suppression subtractive hybridization libraries.

Results

The 1388 unigenes identified in this study were functionally classified based on the Munich Information Center for Protein Sequences (MIPS) categories. The identified proteins were involved in transcriptional regulation, cellular defense and stress, protein degradation, signaling, transport, and secretion, among other functions. Analysis of these unigenes revealed 575 T. rubrum sequences that had not been previously deposited in public databases.

Conclusion

In this study, we identified novel T. rubrum genes that will be useful for ORF prediction in genome sequencing and facilitating functional genome analysis. Annotation of these expressed genes revealed metabolic adaptations of T. rubrum to carbon sources, ambient pH shifts, and various antifungal drugs used in medical practice. Furthermore, challenging T. rubrum with cytotoxic drugs and ambient pH shifts extended our understanding of the molecular events possibly involved in the infectious process and resistance to antifungal drugs.

Over-expression of genes coding for proline oxidase, riboflavin kinase, cytochrome c oxidase and an MFS transporter induced by acriflavin in Trichophyton rubrum

Acriflavin (3,6-acridinediamine) and other acridine derivatives act in both prokaryotic and eukaryotic cells at the level of DNA-coiling enzymes (topoisomerases) causing the stabilization of the enzyme-DNA cleavable complex. In order to better understand the mode of action of acriflavin, Differential Display RT-PCR was used to isolate transcripts specifically over-expressed during exposure of Trichophyton rubrum mycelia to this drug. Five transcripts, whose differential expressions were confirmed by Northern blotting, revealed genes not previously described in this dermatophyte. Functional grouping identified putative enzymes possibly involved in the mitochondrial respiratory electron-transport chain and in iron transport. These results may be relevant to our understanding of the molecular events involved in the stress response of T. rubrum to acriflavin.

Analysis of Trichophyton rubrum gene expression in response to cytotoxic drugs

Suppressive subtractive hybridization was used to isolate transcripts specifically upregulated during Trichophyton rubrum exposure to acriflavin, fluconazole, griseofulvin, terbinafine or undecanoic acid. Macro-array dot-blot and sequencing of 132 clones, which correspond to genes differentially expressed after exposition of T. rubrum to at least one of these cytotoxic drugs, revealed 39 unique genes. Of these, 32 have not been previously described in T. rubrum, representing an increase in the number of T. rubrum genes that have been identified. The upregulation of the novel genes encoding a retrotransposon element, a carboxylic ester hydrolase, a copper resistance-associated P-type ATPase, a DNA mismatch repair protein and a NIMA (never in mitosis A) interactive protein was confirmed by Northern blot.

A transcript finishing initiative for closing gaps in the human transcriptome

We report the results of a transcript finishing initiative, undertaken for the purpose of identifying and characterizing novel human transcripts, in which RT-PCR was used to bridge gaps between paired EST clusters, mapped against the genomic sequence. Each pair of EST clusters selected for experimental validation was designated a transcript finishing unit (TFU). A total of 489 TFUs were selected for validation, and an overall efficiency of 43.1% was achieved. We generated a total of 59,975 bp of transcribed sequences organized into 432 exons, contributing to the definition of the structure of 211 human transcripts. The structure of several transcripts reported here was confirmed during the course of this project, through the generation of their corresponding full-length cDNA sequences. Nevertheless, for 21% of the validated TFUs, a full-length cDNA sequence is not yet available in public databases, and the structure of 69.2% of these TFUs was not correctly predicted by computer programs. The TF strategy provides a significant contribution to the definition of the complete catalog of human genes and transcripts, because it appears to be particularly useful for identification of low abundance transcripts expressed in a restricted set of tissues as well as for the delineation of gene boundaries and alternatively spliced isoforms.

Characterization of alpha-phase soft proton-exchanged LiNbO3 optical waveguides

Waveguides in LiNbO3 are realized by a soft proton exchange (SPE) process with use of a melt of stearic acid highly diluted by lithium stearate. No phase transitions are formed when alpha-phase waveguides are obtained by SPE. The alpha-phase presents the same crystalline structure as that of pure LiNbO3 crystal, and it maintains the excellent nonlinear and electro-optical properties of the bulk material. The kinetics of the SPE method is studied by the use of secondary-ion mass spectrometry and prism-coupling techniques. The hydrogen effective diffusion coefficient as well as the self-diffusion coefficients of H+ and Li+ ions are determined as a function of the proton-exchange temperature for X-cut LiNbO3.