Effect of hemicellulolytic enzymes to improve sugarcane bagasse saccharification and xylooligosaccharides production

Characterization of a multifunctional enzyme from Trichoderma harzianum and its application in enhanced enzymatic hydrolysis

Efficient saccharification of lignocellulose to fermentable sugars is crucial for bioconversion, yet the process is often hindered by insufficient β-glucosidase, β-xylosidase, and α-L-arabinofuranosidase activities in enzyme cocktails from Trichoderma reesei. This study addresses this gap by identifying BX1, a multifunctional enzyme from the underexplored fungus Trichoderma harzianum EM0925, which demonstrates a triad of activities targeting hemicellulose-derived oligosaccharides preferentially. We used structural analysis, molecular docking, and mutation studies to elucidate the roles of specific residues (Asp389, Glu589, Gln185, Cys390, Tyr354, and Tyr526) in BX1's multifunctionality. The enzyme showed synergistic effects with cellulase and xylanase, leading to a 90.23% increase in fermentable sugar yields at 2% (w/v) solid substrate loads and a 22.14% improvement at 15% (w/v) loads when added to Celluclast 1.5L. These findings highlight BX1's potential to enhance lignocellulosic bioconversion efficiency and reduce associated costs, paving the way for more cost-effective saccharification processes and future enzyme engineering advancements.

Optimization of enzymatic hydrolysis of cellulose extracted from bamboo culm for bioethanol production by Saccharomyces cerevisiae modified via CRISPR/Cas9

In the context of biorefinery, researchers have been looking for lignocellulosic biomasses and ideal treatments to produce economically viable biofuels. In this scenario, the bamboo culm appears as a plant matrix of great potential, given the high cellulose content of low crystallinity. Thus, the objective and differential of this work was to determine the best conditions for enzymatic hydrolysis of cellulose extracted from bamboo culm and to evaluate its potential application in the production of bioethanol through Separate Hydrolysis and Fermentation (SHF) and Saccharification and Simultaneous Fermentation (SSF) by Saccharomyces cerevisiae modified via CRISPR/Cas9. The average cellulose extraction yield was 41.87 % with an extraction efficiency of 86.76 %. In general, as the hydrolysis time increased, an increase in glucose production was observed in almost all assays, with higher hydrolysis efficiency values at 72 h. The results ranged from 2.09 to 19.8 g/L of glucose obtained with efficiency values of 10.47 to 99 %. The best conditions were found in test 5 (temperature of 36 °C and pH 5.0, with only 10 FPU/g of substrate Cellic Ctec2 Novozymes ® cocktail). It is observed that for all hydrolysis times the independent variables pH and temperature were significant under the hydrolysis efficiency, showing a negative effect, indicating that higher values of the same promote lower values of the response variable. For bioethanol production, a maximum concentration of 7.84 g/L was observed for the SSH process after 4 h of fermentation, while for the SSF process it was 12.6 g/L after 24 h of fermentation, indicating the large potential of the simultaneous process together with the application of bamboo culm biomass for high production of biofuel.

A metagenomic survey of the fecal microbiome of the African savanna elephant (Loxodonta africana)

The African savanna elephant (Loxodonta africana) is the largest terrestrial animal on Earth and is found primarily in Southern and Eastern Africa. It is a hindgut, colonic fermenter and subsists on a diet of raw plant materials found in its grazing area. In this study the bacterial, archaeal and fungal populations of seven African savanna elephant fecal metagenomes were first characterized using amplicon sequencing. On the genus level it was observed that the p-1088-a5 gut group in the bacteriome, Methanocorpusulum and Methanobrevibacter in the archaeome and Alternaria, Aurobasidium, Didymella and Preussia in the mycome, predominated. Subsequently, metagenomic shotgun sequencing was employed to identify possible functional pathways and carbohydrate-active enzymes (CAZymes). Carbohydrate catabolic pathways represented the main degradation pathways, and the fecal metagenome was enriched in the glycohydroside (GH) class of CAZymes. Additionally, the top GH families identified - GH43, GH2, GH13 and GH3 - are known to be associated with cellulytic, hemicellulytic and pectolytic activities. Finally, the CAZymes families identified in the African savanna elephant were compared with those found in the Asian elephant and it was demonstrated that there is a unique repository of CAZymes that could be leveraged in the biotechnological context such as the degradation of lignocellulose for the production of second-generation biofuels and energy.

Alicyclobacillus mali FL18 as a Novel Source of Glycosyl Hydrolases: Characterization of a New Thermophilic β-Xylosidase Tolerant to Monosaccharides

A thermo-acidophilic bacterium, Alicyclobacillus mali FL18, was isolated from a hot spring of Pisciarelli, near Naples, Italy; following genome analysis, a novel putative β-xylosidase, AmβXyl, belonging to the glycosyl hydrolase (GH) family 3 was identified. A synthetic gene was produced, cloned in pET-30a(+), and expressed in Escherichia coli BL21 (DE3) RIL. The purified recombinant protein, which showed a dimeric structure, had optimal catalytic activity at 80 °C and pH 5.6, exhibiting 60% of its activity after 2 h at 50 °C and displaying high stability (more than 80%) at pH 5.0-8.0 after 16 h. AmβXyl is mainly active on both para-nitrophenyl-β-D-xylopyranoside (K_M 0.52 mM, k_cat 1606 s^-1, and k_cat/K_M 3088.46 mM^-1·s^-1) and para-nitrophenyl-α-L-arabinofuranoside (K_M 10.56 mM, k_cat 2395.8 s^-1, and k_cat/K_M 226.87 mM^-1·s^-1). Thin-layer chromatography showed its ability to convert xylooligomers (xylobiose and xylotriose) into xylose, confirming that AmβXyl is a true β-xylosidase. Furthermore, no inhibitory effect on enzymatic activity by metal ions, detergents, or EDTA was observed except for 5 mM Cu²⁺. AmβXyl showed an excellent tolerance to organic solvents; in particular, the enzyme increased its activity at high concentrations (30%) of organic solvents such as ethanol, methanol, and DMSO. Lastly, the enzyme showed not only a good tolerance to inhibition by xylose, arabinose, and glucose, but was activated by 0.75 M xylose and up to 1.5 M by both arabinose and glucose. The high tolerance to organic solvents and monosaccharides together with other characteristics reported above suggests that AmβXyl may have several applications in many industrial fields.

Use of carbohydrate-directed enzymes for the potential exploitation of sugarcane bagasse to obtain value-added biotechnological products

Microorganisms, such as fungi and bacteria, are crucial players in the production of enzymatic cocktails for biomass hydrolysis or the bioconversion of plant biomass into products with industrial relevance. The biotechnology industry can exploit lignocellulosic biomass for the production of high-value chemicals. The generation of biotechnological products from lignocellulosic feedstock presents several bottlenecks, including low efficiency of enzymatic hydrolysis, high cost of enzymes, and limitations on microbe metabolic performance. Genetic engineering offers a route for developing improved microbial strains for biotechnological applications in high-value product biosynthesis. Sugarcane bagasse, for example, is an agro-industrial waste that is abundantly produced in sugar and first-generation processing plants. Here, we review the potential conversion of its feedstock into relevant industrial products via microbial production and discuss the advances that have been made in improving strains for biotechnological applications.

Production of Xylooligosaccharides from Jiuzao by Autohydrolysis Coupled with Enzymatic Hydrolysis Using a Thermostable Xylanase

The production of xylooligosaccharides (XOS) from Jiuzao was studied using a two-stage process based on autohydrolysis pretreatment followed by enzymatic hydrolysis. Jiuzao was autohydrolyzed under conditions where temperature, time, particle size, and solid-liquid ratio were varied experimentally. Optimal XOS production was obtained from Jiuzao with a >20 mesh particle size treated at 181.5 °C for 20 min with a 1:13.6 solid-liquid ratio. Subsequently, optimal enzymatic hydrolysis conditions for xylanase XynAR were identified as 60 °C, pH 5, and xylanase XynAR loading of 15 U/mL. Using these conditions, a yield of 34.2% XOS was obtained from Jiuzao within 2 h. The process developed in the present study could enable effective and ecofriendly industrial production of XOS from Jiuzao.

Production of xylooligosaccharides, bioethanol, and lignin from structural components of barley straw pretreated with a steam explosion

Barley straw (BS) is a potential source to obtain bioethanol and value-added products such as xylooligosaccharides (XOS) and lignin for application in diverse industries. In this study, BS was submitted to steam explosion pretreatment to valorize the main components of this lignocellulose biomass. For hemicellulose fraction valorization, different combinations of endo-β-(1,4)-D-xylanase enzyme with accessory enzymes (α-L-arabinofuranosidase, feruloy -esterase and acetylxylan-esterase) have been studied to produce XOS with a low degree of polymerization. The application of accessory enzymes combined with endo-β-(1,4)-D-xylanase enzymes turned out to be the most effective strategy for the formation of XOS. The solid fraction obtained after the pretreatment was submitted to presacharification and simultaneous saccharification and fermentation process for bioethanol production. The resulting lignin-rich residue was characterized. In this integrated process, 13.0 g XOS (DP2-DP6), 12.6 g ethanol and 16.6 g lignin were obtained from 100 g of BS, achieving the goal of valorizing this agricultural residue.

Microbial enrichment and meta-omics analysis identify CAZymes from mangrove sediments with unique properties

Although lignocellulose is the most abundant and renewable natural resource for biofuel production, its use remains under exploration because of its highly recalcitrant structure. Its deconstruction into sugar monomers is mainly driven by carbohydrate-active enzymes (CAZymes). To develop highly efficient and fast strategies to discover biomass-degrading enzymes for biorefinery applications, an enrichment process combined with integrative omics approaches was used to identify new CAZymes. The lignocellulolytic-enriched mangrove microbial community (LignoManG) established on sugarcane bagasse (SB) was enriched with lignocellulolytic bacteria and fungi such as Proteobacteria, Bacteroidetes, Basidiomycota, and Ascomycota. These microbial communities were able to degrade up to 55 % of the total SB, indicating the production of lignocellulolytic enzymes. Metagenomic analysis revealed that the LignoManG harbors 18.042 CAZyme sequences such as of cellulases, hemicellulases, carbohydrate esterases, and lytic polysaccharide monooxygenase. Similarly, our metaproteomic analysis depicted several enzymes from distinct families of different CAZy families. Based on the LignoManG data, a xylanase (coldXynZ) was selected, amplified, cloned, expressed, and biochemically characterized. The enzyme displayed psicrofilic properties, with the highest activity at 15 °C, retaining 77 % of its activity when incubated at 0 °C. Moreover, molecular modeling in silico indicated that coldXynZ is composed of a TIM barrel, which is a typical folding found in the GH10 family, and displayed similar structural features related to cold-adapted enzymes. Collectively, the data generated in this study represent a valuable resource for lignocellulolytic enzymes with potential biotechnological applications.

Two-Step Saccharification of the Xylan Portion of Sugarcane Waste by Recombinant Xylanolytic Enzymes for Enhanced Xylose Production

Sugarcane bagasse (SB) and sugarcane trash (SCT) containing 30% hemicellulose content are the waste from the sugarcane industry. Hemicellulose being heterogeneous, more complex, and less abundant than cellulose remains less explored. The optimized conditions for the pretreatment of SB and SCT for maximizing the delignification are soaking in aqueous ammonia (SAA), 18.5 wt %, followed by heating at 70 °C for 14 h. The optimization of hydrolysis of SAA pretreated (ptd) SB and SCT by the Box-Behnken design in the first step of saccharification by xylanase (CtXyn11A) and α-l-arabinofuranosidase (PsGH43_12) resulted in the total reducing sugar (TRS) yield of xylooligosaccharides (TRS_(XOS)) of 93.2 mg/g ptd SB and 85.1 mg/g ptd SCT, respectively. The second step of saccharification by xylosidase (BoGH43) gave the TRS yield of 164.7 mg/g ptd SB and 147.2 mg/g ptd SCT. The high-performance liquid chromatography analysis of hydrolysate obtained after the second step of saccharification showed 69.6% xylan-to-xylose conversion for SB and 64.1% for SCT. This study demonstrated the optimization of the pretreatment method and of the enzymatic saccharification by recombinant xylanolytic enzymes, resulting in the efficient saccharification of ptd hemicellulose to TRS by giving 73.5% conversion for SB and 71.1% for SCT. These optimized conditions for the pretreatment and saccharification of sugarcane waste can also be used at a large scale.

Xylo-oligosaccharide microparticles with synbiotic potential obtained from enzymatic hydrolysis of sugarcane straw

Synbiotic formulations and microencapsulation techniques have been explored in food industries to guarantee the viability of probiotic organisms; playing an important role in microbiota balance. Microparticles of alginate, gelatin and xylo-oligosaccharides (XOS) were produced by external gelation with the purpose of enhancing the survival rate of the probiotic L. acidophilus. XOS was obtained through enzymatic hydrolysis of xylan extracted from sugarcane straw, achieving more than 70% conversion and used for microparticle preparation. Microparticles containing 3% XOS provided greater cell protection during exposure to the gastrointestinal tract and during refrigerated storage; keeping 97.86 ± 0.44% of viability during 28 days of storage and enabling 87.50 ± 0.02% survival after digestive simulation. However, particles without XOS showed 84.49 ± 0.59% of viability after storage and 68.45 ± 0.03% after digestion assay. These results lead to promising applications in synbiotic and functional food formulations comprised of components requiring extended shelf-life, protection from gastrointestinal conditions and gradual bioactive delivery.

Hemicellulases from Penicillium and Talaromyces for lignocellulosic biomass valorization: A review

The term hemicellulose groups different polysaccharides with heterogeneous structures, mannans, xyloglucans, mixed-linkage β-glucans and xylans, which differ in their backbone and branches, and in the type and distribution of glycosidic linkages. The enzymatic degradation of these complex polymers requires the concerted action of multiple hemicellulases and auxiliary enzymes. Most commercial enzymes are produced by Trichoderma and Aspergillus species, but recent studies have disclosed Penicillium and Talaromyces as promising sources of hemicellulases. In this review, we summarize the current knowledge on the hemicellulolytic system of these genera, and the role of hemicellulases in the disruption and synthesis of glycosidic bonds. In both cases, the enzymes from Penicillium and Talaromyces represent an interesting alternative for valorization of lignocellulosic biomass in the current framework of circular economy.

Screening of potential endoglucanases, hydrolysis conditions and different sugarcane straws pretreatments for cello-oligosaccharides production

Cello-oligosaccharides (COS) are oligomers with 2 to 6 β-1,4-linked glucose units, with potential applications in the food/feed and bioenergy industrial sectors. In this study, the combination of five heterologous expressed endoglucanases varying the temperature and pH conditions were evaluated by design of experiments for COS production. Afterwards, the best combination was tested to produce COS from different pretreated sugarcane straws: ionic liquid, diluted acid, hydrothermal and steam-explosion. The results showed that steam explosion pretreated sugarcane straw treated with CtCel9R enzyme at 50 °C and pH 5.0 yielded 13.4 mg COS g biomass^-1, 5-18-fold higher compared to the other pretreated straws. Under the conditions evaluated, the removal of hemicellulose and decrease in the cellulose crystallinity can benefits the enzymatic hydrolysis. This is the first study that combined the evaluation of different enzymes, conditions, and sugarcane straw pretreatments to optimize COS production in a single step without glucose formation.

Low-Cost Cellulase-Hemicellulase Mixture Secreted by Trichoderma harzianum EM0925 with Complete Saccharification Efficacy of Lignocellulose

Fermentable sugars are important intermediate products in the conversion of lignocellulosic biomass to biofuels and other value-added bio-products. The main bottlenecks limiting the production of fermentable sugars from lignocellulosic biomass are the high cost and the low saccharification efficiency of degradation enzymes. Herein, we report the secretome of Trichoderma harzianum EM0925 under induction of lignocellulose. Numerously and quantitatively balanced cellulases and hemicellulases, especially high levels of glycosidases, could be secreted by T. harzianum EM0925. Compared with the commercial enzyme preparations, the T. harzianum EM0925 enzyme cocktail presented significantly higher lignocellulolytic enzyme activities and hydrolysis efficiency against lignocellulosic biomass. Moreover, 100% yields of glucose and xylose were obtained simultaneously from ultrafine grinding and alkali pretreated corn stover. These findings demonstrate a natural cellulases and hemicellulases mixture for complete conversion of biomass polysaccharide, suggesting T. harzianum EM0925 enzymes have great potential for industrial applications.

Designing cellulolytic enzyme systems for biorefinery: From nature to application

Cellulolytic enzymes play a key role on conversion of lignocellulosic plant biomass to biofuels and biochemicals in sugar platform biorefineries. In this review, we survey composite carbohydrate-active enzymes (CAZymes) among groups of cellulolytic fungi and bacteria that exist under aerobic and anaerobic conditions. Recent advances in designing effective cellulase mixtures are described, starting from the most complex microbial consortium-based enzyme preparations, to single-origin enzymes derived from intensively studied cellulase producers such as Trichoderma reesei, Talaromyces cellulolyticus, and Penicellium funiculosum, and the simplest minimal enzyme systems comprising selected sets of mono-component enzymes tailor-made for specific lignocellulosic substrates. We provide a comprehensive update on studies in developing high-performance cellulases for biorefineries.

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.

Protein profile in Aspergillus nidulans recombinant strains overproducing heterologous enzymes

Filamentous fungi are robust cell factories and have been used for the production of large quantities of industrially relevant enzymes. However, the production levels of heterologous proteins still need to be improved. Therefore, this article aimed to investigate the global proteome profiling of Aspergillus nidulans recombinant strains in order to understand the bottlenecks of heterologous enzymes production. About 250, 441 and 424 intracellular proteins were identified in the control strain Anid_pEXPYR and in the recombinant strains Anid_AbfA and Anid_Cbhl respectively. In this context, the most enriched processes in recombinant strains were energy pathway, amino acid metabolism, ribosome biogenesis, translation, endoplasmic reticulum and oxidative stress, and repression under secretion stress (RESS). The global protein profile of the recombinant strains Anid_AbfA and Anid_Cbhl was similar, although the latter strain secreted more recombinant enzyme than the former. These findings provide insights into the bottlenecks involved in the secretion of recombinant proteins in A. nidulans, as well as in regard to the rational manipulation of target genes for engineering fungal strains as microbial cell factories.