Production of xylanase and β-xylosidase from autohydrolysis liquor of corncob using two fungal strains

Characterization of the complete mitochondrial genome of Aspergillus terricola (Aspergillaceae, Eurotiales), isolated from soy sauce fermentation system

In the present study, the complete mitochondrial genome of Aspergillus terricola É.J. Marchal 1893 was sequenced and assembled. The mitochondrial genome of A. terricola was composed of circular DNA molecules, with a total size of 28,689 bp. The GC content of the A. terricola mitochondrial genome was 26.34%. A total of 18 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, and 26 transfer RNA (tRNA) genes were detected in the A. terricola mitochondrial genome. Phylogenetic analysis based on the combined mitochondrial gene dataset indicated that the A. terricola exhibited a close relationship with A. parasiticus.

Cloning and characterization of the β-xylosidase from Dictyoglomus turgidum for high efficient biotransformation of 10-deacetyl-7-xylosltaxol

With the aim of finding an extracellular biocatalyst that can efficiently remove the C-7 xylose group from 10-deacetyl-7-xylosltaxol, a Dictyoglomus turgidum β-xylosidase was cloned and expressed in Escherichia coli BL21 (DE3). The molecular mass of purified Dt-Xyl3 was approximately 84 kDa. The recombinant Dt-Xyl3 was most active at pH 5.0 and 75 °C, retaining 88% activity at 65 °C for 1 h, and displaying excellent stability over pH 4.0-7.5 for 24 h. In terms of kinetic parameters, the K_m and V_max values for pNPX were 0.8316 mM and 5.0178 μmol/mL·min, respectively. Moreover, Dt-Xyl3 was activated by Mn²⁺ and Ba²⁺ and inhibited by Cu²⁺, Ni⁺ and Al³⁺. In particular, it displayed high tolerance to salts with 60.8% activity in 20% (w/v) NaCl. Ethanol and methanol at 5-15% showed little effect on the enzymatic activity. Dt-Xyl3 demonstrated multifunctional activities followed by pNPX, pNPAraf and pNPG and had a high selectivity for cleaving the outer xylose moieties of 10-deacetyl-7-xylosltaxol with K_cat/K_m 110.87 s^-1/mM, which produced 10-deacetyl-taxol to semi-synthesize paclitaxel. Under the optimized conditions (60 °C, pH 4.5, enzyme dosage of 0.5 U/mL), 1 g of 10-deacetyl-7-xylosltaxol was transformed to its corresponding aglycone 10-deacetyl-taxol within 30 min, with a molar conversion of 98%. This is the first report that Dictyoglomus turgidum can produce extracellular GH3 β-xylosidase with highly specific activity for 10-deacetyl-7-xylosltaxol biotransformation, thus leading to the application of β-xylosidase Dt-Xyl3 as a biocatalyst in biopharmaceutics.

Mycoviruses mediate mycotoxin regulation in Aspergillus ochraceus

To date, no demonstration of a direct correlation between the presence of mycoviruses and the quantitative or qualitative modulation of mycotoxins has been shown. In our study, we transfected a virus-free ochratoxin A (OTA)-producing isolate of Aspergillus ochraceus with purified mycoviruses from a different A. ochraceus isolate and from Penicillium aurantiogriseum. Among the mycoviruses tested, only Aspergillus ochraceus virus (AoV), a partitivirus widespread in A. ochraceus, caused a specific interaction that led to an overproduction of OTA, which is regulated by the European Commission and is the second most important contaminant of food and feed commodities. Gene expression analysis failed to reveal a specific viral upregulation of the mRNA of genes considered to play a role in the OTA biosynthetic pathway. Furthermore, AoOTApks1, a polyketide synthase gene considered essential for OTA production, is surprisingly absent in the genome of our OTA-producing isolate. The possible biological and evolutionary implications of the mycoviral regulation of mycotoxin production are discussed.

Prospecting of soybean hulls as an inducer carbon source for the cellulase production

Cellulases constitute an enzymatic complex involved in the cellulose hydrolysis β-1, 4-glycosidic linkages to release of glucose. Therefore, its application to degrade agro-industrial residues becomes relevant, since glucose is a product of industrial interest, aiming at its conversion into biocommodity production (e.g., enzymes, bioethanol and other value-added biochemicals). Thus, in natura Soybean hulls as well as fractions obtained from its alkaline, autohydrolysis and organosolv pretreatments were used as carbon sources in submerged fermentation processes to evaluate the cellulase-inducing capacity using a Penicillium sp. strain. Results showed an inductive effect on the production of 0.130 and 0.066 U/mL for CMCase and FPase, respectively, using 1% of the in natura residue. Regarding the fraction obtained from soybean hulls pretreated by autohydrolysis and organosolv, avicelase and β-Glucosidase displayed a production of 0.200 and 0.550 U/mL, respectively. Therefore, the use of pretreated Soybean hull revealed its potential as an alternative carbon source for the cellulase production, which may contribute significantly to biotechnological purposes by adding value to an agro-industrial residue.

Characterization of a novel thermostable and xylose-tolerant GH 39 β-xylosidase from Dictyoglomus thermophilum

Background

β-D-xylosidase is a vital exoglycosidase with the ability to hydrolyze xylooligosaccharides to xylose and to biotransform some saponins by cleaving outer β-xylose. β-D-xylosidase is widely used as one of the xylanolytic enzymes in a diverse range of applications, such as fuel, food and the pharmaceutical industry; therefore, more and more studies have focused on the thermostable and xylose-tolerant β-D-xylosidases.

Results

A thermostable β-xylosidase gene (xln-DT) of 1509 bp was cloned from Dictyoglomus thermophilum and expressed in E.coli BL21. According to the amino acid and phylogeny analyses, the β-xylosidase Xln-DT is a novel β-xylosidase of the GH family 39. The recombinant β-xylosidase was purified, showing unique bands on SDS-PAGE, and had a protein molecular weight of 58.7 kDa. The β-xylosidase Xln-DT showed an optimal activity at pH 6.0 and 75 °C, with p-nitrophenyl-β-D-xylopyranoside (pNPX) as a substrate. Xln-DT displayed stability over a pH range of 4.0-7.5 for 24 h and displayed thermotolerance below 85 °C. The values of the kinetic parameters K_m and V_max for pNPX were 1.66 mM and 78.46 U/mg, respectively. In particular, Xln-DT displayed high tolerance to xylose, with 60% activity in the presence of 3 M xylose. Xln-DT showed significant effects on the hydrolyzation of xylobiose. After 3 h, all the xylobiose tested was degraded into xylose. Moreover, β-xylosidase Xln-DT had a high selectivity for cleaving the outer xylose moieties of natural saponins, such as notoginsenoside R1 and astragaloside IV, which produced the ginsenoside Rg1 with stronger anti-fatigue activity and produced cycloastragenol with stronger anti-aging activity, respectively.

Conclusion

This study provides a novel GH 39 β-xylosidase displaying extraordinary properties of highly catalytic activity at temperatures above 75 °C, remarkable hydrolyzing activity of xylooligosaccharides and rare saponins producing ability in the pharmaceutical and commercial industries.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0440-3) contains supplementary material, which is available to authorized users.

Multi-step approach to add value to corncob: Production of biomass-degrading enzymes, lignin and fermentable sugars

This work presents an integrated and multi-step approach for the recovery and/or application of the lignocellulosic fractions from corncob in the production of high value added compounds as xylo-oligosaccharides, enzymes, fermentable sugars, and lignin in terms of biorefinery concept. For that, liquid hot water followed by enzymatic hydrolysis were used. Liquid hot water was performed using different residence times (10-50min) and holding temperature (180-200°C), corresponding to severities (log(R₀)) of 3.36-4.64. The most severe conditions showed higher xylo-oligosaccharides extraction (maximum of 93%) into the hydrolysates and higher recovery of cellulose on pretreated solids (maximum of 65%). Subsequently, hydrolysates and solids were used in the production of xylanases and cellulases, respectively, as well as, pretreated solids were also subjected to enzymatic hydrolysis for the recovery of lignin and fermentable sugars from cellulose. Maximum glucose yield (100%) was achieved for solids pretreated at log(R₀) of 4.42 and 5% solid loading.

Liquid hot water pretreatment of multi feedstocks and enzymatic hydrolysis of solids obtained thereof

Agricultural feedstocks (brewers' spent grain - BSG, corncob - CC, corn husk - CH, wheat straw - WS and Luffa sponge - LS) were pretreated by liquid hot water (LHW) in order to increase cellulose recovery and enzymatic saccharification. LHW-pretreatment resulted in hemicellulose solubilization, and solids enriched in cellulose. Chemical analysis showed different susceptibilities of the feedstocks to LHW-pretreatment and enzymatic hydrolysis. Pretreated feedstocks presented higher crystallinity (determined through X-ray diffraction) and thermal stability (determined through thermogravimetric analysis) than untreated feedstocks. SEM images confirmed the effect of LHW-pretreatment on structural changes. Moreover, enzymatic hydrolysis and cellulose conversion to glucose (CCG) were improved for pretreated feedstocks, with exception of LS. CCG (in relation to glucose potential on solids) followed the order: BSG>CH>WS>CC>LS. LHW-pretreatment showed to be a good technology to pretreat multi feedstocks and for improving the enzymatic hydrolysis of recalcitrant agricultural feedstocks to sugars, which can be further converted to ethanol-fuel and other value-added chemicals.

Screening of thermotolerant and thermophilic fungi aiming β-xylosidase and arabinanase production

Plant cell wall is mainly composed by cellulose, hemicellulose and lignin. The heterogeneous structure and composition of the hemicellulose are key impediments to its depolymerization and subsequent use in fermentation processes. Thus, this study aimed to perform a screening of thermophilic and thermotolerant filamentous fungi collected from different regions of the São Paulo state, and analyze the production of β-xylosidase and arabinanase at different temperatures. These enzymes are important to cell wall degradation and synthesis of end products as xylose and arabinose, respectively, which are significant sugars to fermentation and ethanol production. A total of 12 fungal species were analyzed and 9 of them grew at 45 °C, suggesting a thermophilic or thermotolerant character. Additionally Aspergillus thermomutatus anamorph of Neosartorya and A. parasiticus grew at 50 °C. Aspergillus niger and Aspergillus thermomutatus were the filamentous fungi with the most expressive production of β-xylosidase and arabinanase, respectively. In general for most of the tested microorganisms, β-xylosidase and arabinanase activities from mycelial extract (intracellular form) were higher in cultures grown at high temperatures (35–40 °C), while the correspondent extracellular activities were favorably secreted from cultures at 30 °C. This study contributes to catalogue isolated fungi of the state of São Paulo, and these findings could be promising sources for thermophilic and thermotolerant microorganisms, which are industrially important due to their enzymes.

Mini-review: Brazilian fungi diversity for biomass degradation

Brazil houses over 10% of the total number of known species on Earth, with a great diversity of plants and fungi. The collection, isolation, identification and conservation of filamentous fungi with relevance to agriculture, pharmaceutical, food and biotechnological industries in Biological Resource Centers (CRBs) is very important to the development of a nation's scientific and technological infrastructure. In Brazil, 36 fungal collections are registered in the database of International Collections. Several federal and state programs have encouraged the formation of a researcher's network in order to study natural resources and the nation's biodiversity. In this context, Brazilian researchers have been on the frontiers of knowledge, investigating the enzymatic systems from native filamentous fungi with potential for biomass degradation and biotechnological application. In this review, we address recent progress in Brazilian fungal research, focusing on the identification and study of fungi and enzymes with potential for biomass degradation and application in bioenergy.

Production of intracellular β-xylosidase from the submerged fermentation of citrus wastes by Penicillium janthinellum MTCC 10889

Production of intracellular β-xylosidase was studied in cultures of Penicillium janthinellum grown on citrus fruit waste supplemented cultivation media. Both dried orange peel and sweet lime peel could induce the production of this enzyme. The working strain showed a pronounced optimum pH and temperature for β-xylosidase production at 6.0 and 27 °C, respectively. The enzyme production was found to remain stable for a long period of 120 h. Orange peel and sweet lime peel showed different responses in the presence of various nitrogen sources, probably due to their differences in hemicellulosic contents. This could be further confirmed by the difference in enzyme production after pretreatment with acid and alkali.