Optimization of xylanase production from Aspergillus niger for biobleaching of eucalyptus pulp

Enhanced Production, Cloning, and Expression of a Xylanase Gene from Endophytic Fungal Strain Trichoderma harzianum kj831197.1: Unveiling the In Vitro Anti-Fungal Activity against Phytopathogenic Fungi

Trichoderma sp. is extensively applied as a beneficial fungus for the management of plant diseases, plant growth promotion, induced resistance, and plays an important role in global sustainable agriculture. This study aimed to enhance the production of microbial xylanase in high titer from the endophytic fungus Trichoderma harzianum kj831197.1, and the cloning of xylanase genes in E. coli DH5α using a pUC19 vector. A combination of glucose, 0.1 mM, Tween 80 with lactose, and 2 mM galactose combined with malt extract boostedthe enzyme production. Xylanase production was maximized at a pH of 5.0, temp. of 30 °C, and agitation of 150 rpm in the presence of malt extract and bagasse as the best nitrogen source and waste, respectively, using submerged fermentation. The molecular weight of highly purified xylanase was 32 KDa, identified using SDS-PAGE. The xylanase gene of T. harzianum kj831197.1 was screened in fungal DNA using definite primers specified in the gene bank database. The identified region was excised using restriction enzymes HindIII and EcoRI and cloned into a pUC19 plasmid vector. Optimization of fermentation conditions improved xylanase production about 23.9-fold.The antifungal efficacy of xylanase toward different phytopathogenic fungi was determined. The highest inhibition was against Corynespora cassiicola, Alternaria sp., Fusarium oxysporum, and Botrytis fabae. This study offered an economical, simple, and efficient method using Trichoderma harzianum kj831197.1 for the production of the xylanase enzyme via the submerged fermentation method.

Profiling multi-enzyme activities of Aspergillus niger strains growing on various agro-industrial residues

Agro-industrial wastes provide potential sources of carbon for production of fungal enzymes applied for various biotechnological applications. In this study, 23 strains of Aspergillus niger were systematically investigated for their capability on production of carbohydrate-processing enzymes used in industries. The strains were grown on glucose or selected agricultural wastes comprising varied chemical compositions as the sole carbon source. As a control, glucose induced basal activities of amylase, pectinase, and xylanase in only a few strains, while the CMCase, β-glucanase, and invertase activities were detected only when the carbon source was switched to the agro-industrial biomass. According to one-way ANOVA analysis, banana peels containing lignocellulosic components with high pectin and starch contents with its easily digestible nature, were found to be the best carbon source for inducing production of most target enzymes, while the cellulose-rich sugarcane bagasse efficiently promoted maximal levels of β-glucanase and xylanase activities. The starch fiber-rich cassava pulp also effectively supported the activities of amylase and most other enzymes, but at relatively lower levels compared to those obtained with banana peel. The A. niger TL11 strain was considered the most potent strain for production of all target enzymes with the CMCase, xylanase, pectinase, β-glucanase, amylase, and invertase activities of 76.15, 601.59, 160.89, 409.20, 426.73, and 1186.94 U/mL, respectively. The results provide insights into the efficiency of various carbon sources with different chemical compositions on inducing the target enzymes as well as the dissimilarity of A. niger strains on the production of different carbohydrate-processing enzymes.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03086-y.

A Comprehensive Insight into Fungal Enzymes: Structure, Classification, and Their Role in Mankind's Challenges

Enzymes have played a crucial role in mankind's challenges to use different types of biological systems for a diversity of applications. They are proteins that break down and convert complicated compounds to produce simple products. Fungal enzymes are compatible, efficient, and proper products for many uses in medicinal requests, industrial processing, bioremediation purposes, and agricultural applications. Fungal enzymes have appropriate stability to give manufactured products suitable shelf life, affordable cost, and approved demands. Fungal enzymes have been used from ancient times to today in many industries, including baking, brewing, cheese making, antibiotics production, and commodities manufacturing, such as linen and leather. Furthermore, they also are used in other fields such as paper production, detergent, the textile industry, and in drinks and food technology in products manufacturing ranging from tea and coffee to fruit juice and wine. Recently, fungi have been used for the production of more than 50% of the needed enzymes. Fungi can produce different types of enzymes extracellularly, which gives a great chance for producing in large amounts with low cost and easy viability in purified forms using simple purification methods. In the present review, a comprehensive trial has been advanced to elaborate on the different types and structures of fungal enzymes as well as the current status of the uses of fungal enzymes in various applications.

Evaluation of nutraceutical application of xylooligosaccharide enzymatically produced from cauliflower stalk for its value addition through a sustainable approach

There is increasing attention on the exploration of waste feedstocks as economically viable substrates for the production of prebiotic oligosaccharides, especially xylooligosaccharides, as excellent candidates for the maintenance and promotion of gut microbiota. XOS, an emerging prebiotic that has several functional attributes and beneficial health effects, is mainly produced by different processes, especially enzymatic hydrolysis through the valorisation of xylan enriched lignocellulosic materials. The present study deals with the enzymatic production of xylooligosaccharide (XOS) from xylan rich cauliflower stalk, a novel source. Delignification with alkali (NaOH) was found to be more efficient than acid and autohydrolysis, resulting in a higher extraction yield of xylan (18.42%). Alkaline extraction for 120 minutes at 1.25 M alkali concentration produced maximum xylan yield. FTIR analysis of xylan extracted from cauliflower stalk by an alkaline (NaOH) pretreatment method showed typical absorption bands at 1729 cm-1 that correspond to acetyl groups exhibiting the typical xylan specific band. Enzymatic hydrolysis was carried out with indigenously produced crude endoxylanase obtained from Aspergillus niger MTCC 9687 and the effects of substrate concentration, enzyme concentration, pH, time and temperature were investigated. High resolution MS analysis showed the presence of xylobiose as the major XOS. The major 1H spectral signals of XOS liberated from enzymatically hydrolysed alkali extracted cauliflower stalk xylan showed the presence of β-anomeric protons in the spectral region of 4.0-4.7 ppm. Prebiotic efficacy of cauliflower stalk derived XOS alone and synbiotic combinations with known probiotic strains (Lactiplantibacillus plantarum, Bifidobacterium bifidum, Lactobacillus delbrueckii ssp. Helveticus) were evaluated. Butyrate was found to be the major short chain fatty acid produced by XOS supplemented fermentation media. All the synbiotic combinations showed significantly higher antioxidant and antimicrobial activities and reduced the viability of human bone cancer MG-63 cells. The individual profiles of antimicrobial components of XOS were identified as dihydroxy benzoic acid and aspartic acid by HPLC coupled to a photodiode array detector.

Biobleaching: An eco-friendly approach to reduce chemical consumption and pollutants generation

The pulp and paper industry is known to be a large contributor to environmental pollution due to the huge consumption of chemicals and energy. Several chemicals including H2SO4, Cl2, ClO2, NaOH, and H2O2 are used during the bleaching process. These chemicals react with lignin and carbohydrates to generate a substantial amount of pollutants in bleach effluents. Environmental pressure has compelled the pulp and paper industry to reduce pollutant generation from the bleaching section. Enzymes have emerged as simple, economical, and eco-friendly alternatives for bleaching of pulp. The pretreatment of pulp with enzymes is termed as biobleaching or pre-bleaching. Different microbial enzymes such as xylanases, pectinases, laccases, manganese peroxidases (MnP), and lignin peroxidases are used for biobleaching. Xylanases depolymerize the hemicelluloses precipitated on pulp fiber surfaces and improves the efficiency of bleaching chemicals. Xylanase treatment also increases the pulp fibrillation and reduces the beating time of the pulp. Pectinases hydrolyze pectin available in the pulp fibers and improve the papermaking process. Laccase treatment is found more effective along with mediator molecules (as a laccase-mediator system). Biobleaching of pulp results in the superior quality of pulp along with lower consumption of chlorine-based chemicals and lower generation of adsorbable organic halidesadsorbable organic halides (AOX. An enzyme pretreatment reduces the kappa number of pulp and improves ISO brightness significantly. Better physical strength properties and pulp viscosity have also been observed during biobleaching of pulp.

Understanding the structural and functional properties of carbohydrate esterases with a special focus on hemicellulose deacetylating acetyl xylan esterases

Acetyl and methyl esterifications are two major naturally found substitutions in the plant cell-wall polysaccharides. The non-cellulosic plant cell-wall polysaccharides such as pectin and hemicellulose are differentially esterified by the O-acetyl and methyl groups to cease the action of various hydrolytic enzymes secreted by different fungi and bacterial species. Thus, microorganisms have emerged with a special class of enzymes known as carbohydrate esterases (CE). The CE catalyse O-de, N-deacetylation of acetylated saccharide residues (esters or amides, where sugars play the role of alcohol/amine/acid). Carbohydrate active enzyme (CAZy) database has classified CE into 16 classes, of which hemicellulose deacetylating CE were grouped into eight classes (CE-1 to CE-7 and CE-16). Various plant biomass degrading fungi and bacteria secretes acetyl xylan esterases (AcXE); however, these enzymes exhibit varied substrate specificities. AcXE and xylanases-coupled pretreatment methods exhibit significant applications, such as enhancing animal feedstock, baking industry, production of food additives, paper and pulp, xylitol production and biorefinery-based industries, respectively. Thus, understanding the structural and functional properties of acetyl xylan esterase will significantly aid in developing the efficient AcXE with wide range of industrial applications.

Microbial xylanases and their industrial application in pulp and paper biobleaching: a review

Xylanases are hydrolytic enzymes which cleave the β-1, 4 backbone of the complex plant cell wall polysaccharide xylan. Xylan is the major hemicellulosic constituent found in soft and hard food. It is the next most abundant renewable polysaccharide after cellulose. Xylanases and associated debranching enzymes produced by a variety of microorganisms including bacteria, actinomycetes, yeast and fungi bring hydrolysis of hemicelluloses. Despite thorough knowledge of microbial xylanolytic systems, further studies are required to achieve a complete understanding of the mechanism of xylan degradation by xylanases produced by microorganisms and their promising use in pulp biobleaching. Cellulase-free xylanases are important in pulp biobleaching as alternatives to the use of toxic chlorinated compounds because of the environmental hazards and diseases caused by the release of the adsorbable organic halogens. In this review, we have focused on the studies of structural composition of xylan in plants, their classification, sources of xylanases, extremophilic xylanases, modes of fermentation for the production of xylanases, factors affecting xylanase production, statistical approaches such as Plackett Burman, Response Surface Methodology to enhance xylanase production, purification, characterization, molecular cloning and expression. Besides this, review has focused on the microbial enzyme complex involved in the complete breakdown of xylan and the studies on xylanase regulation and their potential industrial applications with special reference to pulp biobleaching, which is directly related to increasing pulp brightness and reduction in environmental pollution.

Biocatalytic activity of Aspergillus niger xylanase in paper pulp biobleaching

Xylanase is a hemicellulase enzyme that catalyses the hydrolysis of xylan to xylose which is widely used in processing of feed, pulp and paper. It is produced by many microorganisms especially filamentous fungi like Trichoderma and Aspergillus. A potential xylanolytic fungal isolate Aspergillus niger was isolated from forest soils of Tirumala, AP, India, and its crude enzyme was checked for its potential in paper bleaching. Under submerged fermentation, production of xylanase, cellulase, biomass, total protein and sugar released were analysed after 7 days of incubation at room temperature. Maximum enzyme activity was recorded on the fifth day of incubation, biomass after the seventh day, total protein and sugar released on the sixth day of incubation. Enzyme pretreatment of paper reduced 3.5 points in kappa number, 3.1 points increase in brightness and removal of chromophores and hydrophobic compounds. The FTIR and SEM analysis of enzyme-treated sample had shown modification in surface morphology and functional groups. These results clearly demonstrated that the xylanase produced by A. niger was effective as a pulp biobleaching agent which can be used on an industrial scale.

Modification in the properties of paper by using cellulase-free xylanase produced from alkalophilic Cellulosimicrobium cellulans CKMX1 in biobleaching of wheat straw pulp

Alkalophilic Cellulosimicrobium cellulans CKMX1 isolated from mushroom compost is an actinomycete that produces industrially important and environmentally safer thermostable cellulase-free xylanase, which is used in the pulp and paper industry as an alternative to the use of toxic chlorinated compounds. Strain CKMX1 was previously characterized by metabolic fingerprinting, whole-cell fatty acids methyl ester analysis, and 16S rDNA and was found to be C. cellulans CKMX1. Crude enzyme (1027.65 U/g DBP) produced by C. cellulans CKMX1, having pH and temperature optima of 8.0 and 60 °C, respectively, in solid state fermentation of apple pomace, was used in the production of bleached wheat straw pulp. Pretreatment with xylanase at a dose of 5 U/g after pulping decreased pulp kappa points by 1.4 as compared with the control. Prebleaching with a xylanase dose of 5 U/g pulp reduced the chlorine charge by 12.5%, increased the final brightness points by approximately 1.42% ISO, and improved the pulp strength properties. Xylanase could be substituted for alkali extraction in C–Ep–D sequence and used for treating chemically bleached pulp, resulting in bleached pulp with higher strength properties. Modification of bleached pulp with 5 U of enzyme/g increased pulp whiteness and breaking length by 1.03% and 60 m, respectively; decreased tear factor of pulp by 7.29%; increased bulk weight by 3.99%, as compared with the original pulp. Reducing sugars and UV-absorbing lignin-derived compound values were considerably higher in xylanase-treated samples. Cellulosimicrobium cellulans CKMX1 has a potential application in the pulp and paper industries.

β-Mannanase production by Aspergillus niger BCC4525 and its efficacy on broiler performance

BACKGROUND

Mannan is a hemicellulose constituent commonly found in plant-derived feed ingredients. The gum-like property of mannan can obstruct digestive enzymes and bile acids, resulting in impaired nutrient utilisation. In this study, β-mannanase production by Aspergillus niger strain BCC4525 was investigated using several agricultural residues under solid state condition. The biochemical properties of the target enzyme and the effects of enzyme supplementation on broiler performance and energy utilisation were assessed.

RESULTS

Among five carbon sources tested, copra meal was found to be the best carbon source for β-mannanase production with the maximum yield of 1837.5 U g(-1) . The crude β-mannanase exhibited maximum activity at 80 °C within a broad range of pH from 2 to 6. In vitro digestibility assay, which simulates the gastrointestinal tract system of broilers, showed that β-mannanase could liberate reducing sugars from corn/soybean diet. Surprisingly, β-mannanase supplementation had no significant effect on broiler feed intake, feed conversion rate or energy utilisation.

CONCLUSION

A high level of β-mannanase was produced by A. niger BCC4525 under solid state condition using copra meal as carbon source. Although the enzyme has the desired properties of an enzyme additive for improving broiler performance, it does not appear to be beneficial.

Bioprocess and biotecnology: effect of xylanase from Aspergillus niger and Aspergillus flavus on pulp biobleaching and enzyme production using agroindustrial residues as substract

This study compares two xylanases produced by filamentous fungi such as A. niger and A. flavus using agroindustrial residues as substract and evaluated the effect of these enzymes on cellulose pulp biobleaching process. Wheat bran was the best carbon source for xylanase production by A. niger and A. flavus. The production of xylanase was 18 and 21% higher on wheat bran when we compare the xylanase production with xylan. At 50°C, the xylanase of A. niger retained over 85% activity with 2 h of incubation, and A. flavus had a half-life of more than 75 minutes. At 55°C, the xylanase produced by A. niger showed more stable than from A. flavus showing a half-life of more than 45 minutes. The xylanase activity of A. niger and A. flavus were somehow protected in the presence of glycerol 5% when compared to the control (without additives). On the biobleaching assay it was observed that the xylanase from A. flavus was more effective in comparison to A. niger. The kappa efficiency corresponded to 36.32 and 25.93, respectively. That is important to emphasize that the cellulase activity was either analyzed and significant levels were not detected, which explain why the viscosity was not significantly modified.

Isolation and characterization of a novel GH67 α-glucuronidase from a mixed culture

Hemicelluloses represent a large reservoir of carbohydrates that can be utilized for renewable products. Hydrolysis of hemicellulose into simple sugars is inhibited by its various chemical substituents. The glucuronic acid substituent is removed by the enzyme α-glucuronidase. A gene (deg75-AG) encoding a putative α-glucuronidase enzyme was isolated from a culture of mixed compost microorganisms. The gene was subcloned into a prokaryotic vector, and the enzyme was overexpressed and biochemically characterized. The DEG75-AG enzyme had optimum activity at 45 °C. Unlike other α-glucuronidases, the DEG75-AG had a more basic pH optimum of 7–8. When birchwood xylan was used as substrate, the addition of DEG75-AG increased hydrolysis twofold relative to xylanase alone.