Eco-friendly Bleaching of Agrowaste Wheat Straw Using Crude Alkalo-Thermotolerant Cellulase-Free Xylano-Pectinolytic Enzymes

The aim of this study was to evaluate the potential of xylanase-pectinase enzymes in bleaching of wheat straw pulp, just to cut down the toxic wastes, in order to manage the environmental pollution. The appropriate parameters of bleaching were evaluated, and best conditions were xylanase and pectinase dose of 5.0 and 1.66 IU/g of pulp, respectively, along with material to liquid ratio of 1:7.5 (g/ml), temperature 55 °C, treatment time 3 h, Tween-80 1%, and pH 8.5. The release of reducing sugar and other non-cellulosic impurities, phenolic-hydrophobic-lignin was maximum at best bleaching conditions. Prebleaching of wheat straw pulp using these enzymes showed 14.75% decline in kappa number. Enzymatic bleaching plus 100% chemical bleaching also led to 27.90% reduction in yellowness. Using this methodology, the consumption of active chlorine was reduced up to 25%, along with an increase in burst index (7.98%), tear index (3.42%), breaking length (5.30%), viscosity (11.22%), gurley porosity (12.50%), and double-fold number (23.08%), which exhibits a remarkable enhancement in all the properties of pulp treated with enzymes. Microscopic images also confirm the effectiveness of enzymatic treatment in bleaching of wheat straw pulp. BOD and COD values of effluent also decreased by 20.74 and 17.87%, respectively. This research focussing on producing better grade paper using an eco-friendly approach would certainly benefit the paper and pulp industry. This is the first report, depicting bleaching capability of xylanase-pectinase enzymes for soda-anthraquinone pulp of wheat straw.

Evaluation of temperature, pH and nutrient conditions in bacterial growth and extracellular hydrolytic activities of two Alicyclobacillus spp. strains

Extremophile bacteria have developed the metabolic machinery for living in extreme temperatures, pH, and high-salt content. Two novel bacterium strains Alicyclobacillus sp. PA1 and Alicyclobacillus sp. PA2, were isolated from crater lake El Chichon in Chiapas, Mexico. Phylogenetic tree analysis based on the 16SrRNA gene sequence revealed that the strain Alicyclobacillus sp. PA1 and Alicyclobacillus sp. PA2 were closely related to Alicyclobacillus species (98% identity and 94.73% identity, respectively). Both strains were Gram variable, and colonies were circular, smooth and creamy. Electron microscopy showed than Alicyclobacillus sp. PA1 has a daisy-like form and Alicyclobacillus sp. PA2 is a regular rod. Both strains can use diverse carbohydrates and triglycerides as carbon source and they also can use organic and inorganic nitrogen source. But, the two strains can grow without any carbon or nitrogen sources in the culture medium. Temperature, pH and nutrition condition affect bacterial growth. Maximum growth was produced at 65 °C for Alicyclobacillus sp. PA1 (0.732 DO₆₀₀) at pH 3 and Alicyclobacillus sp. PA2 (0.725 DO₆₀₀) at pH 5. Inducible extracellular extremozyme activities were determined for β-galactosidase (Alicyclobacillus sp. PA1: 88.07 ± 0.252 U/mg, Alicyclobacillus sp. PA2: 51.57 ± 0.308 U/mg), cellulose (Alicyclobacillus sp. PA1: 141.20 ± 0.585 U/mg, Alicyclobacillus sp. PA2: 51.57 ± 0.308 U/mg), lipase (Alicyclobacillus sp. PA1: 138.25 ± 0.600 U/mg, Alicyclobacillus sp. PA2: 175.75 ± 1.387 U/mg), xylanase (Alicyclobacillus sp. PA1: 174.72 ± 1.746 U/mg, Alicyclobacillus sp. PA2: 172.69 ± 0.855U/mg), and protease (Alicyclobacillus sp. PA1: 15.12 ± 0.121 U/mg, Alicyclobacillus sp. PA2: 15.33 ± 0.284 U/mg). These results provide new insights on extreme enzymatic production on Alicyclobacillus species.

Potential of crude xylano-pectinolytic enzymes in bleaching of rice straw pulp for improving paper quality and reducing toxic effluent load generation

The objective of this study was to check the potential of crude xylano-pectinolytic enzymes in bleaching of rice straw pulp, in order to reduce the toxic waste load for managing the environmental pollution. The xylano-pectinolytic enzymatic bleaching step for delignification was found to be most effective at pulp consistency 1:10 g/ml, xylanase:pectinase dose of 9:4 IU/ml, pH 8.5 and treatment time 180 min at temperature of 55 °C, and resulted in lowering of kappa number of the rice straw pulp by 15.29%. In subsequent bleaching stages, this enzymatic pre-bleaching treatment also resulted in 30% reduction of active chlorine dioxide dose without any loss of optical properties. Significant improvement in various physical properties of the enzymes treated pulp, tear index (15.43%), breaking length (11.11%), double fold number (25.92%), burst index (9.88%) and viscosity (13.63%), and Gurley porosity (39.86%) was also noticed. This approach resulted in reduction of BOD and COD values by 21.07% and 26.57%, respectively. This is the first study on the use of crude xylano-pectinolytic enzymes for bio-bleaching of rice straw pulp.

Synergistic approach using ultrafiltered xylano-pectinolytic enzymes for reducing bleaching chemical dose in manufacturing rice straw paper

In this study, action of ultrafiltered xylano-pectinolytic enzymes from a bacterial strain has been evaluated for bleaching of rice straw soda-anthraquinone pulp. Maximum bio-bleaching effect and release of non-cellulosic impurities were noticed with xylano:pectinolytic enzymes dose of 6.0:2.1-IU/g pulp, treatment time of 180 min at 10% pulp consistency, pH 8.5, and temperature 55 °C. Microscopic images of bio-bleached rice straw pulp also confirmed the efficacy of ultrafiltered enzymes, as bleaching agent. This bio-bleaching treatment resulted in 15.38% and 32% reduction in kappa number and active chlorine dioxide dose, respectively, along with increase in various physical properties, burst index (12.50%), tear index (19.07%), breaking length (14.30%), double fold number (26.31%), Gurley porosity (45.32%) and viscosity (16.17%). This bio-bleaching approach not only improved the pulp quality but also reduced environmental pollution load by decreasing effluent parameters values of BOD and COD by 23.67% and 27.44%, respectively. This study indicates that use of ultrafiltered xylano-pectinolytic synergism for rice straw pulp bleaching will ultimately help in making the process eco-friendly, along with better quality pulp. This is the first report on use of ultrafiltered xylanase and pectinase, produced from a bacterial isolate, for bleaching of rice straw pulp.

A thermophilic and thermostable xylanase from Caldicoprobacter algeriensis: Recombinant expression, characterization and application in paper biobleaching

A novel xylanase gene xynBCA, encoding a polypeptide of 439 residues (XynBCA), was cloned from Caldicoprobacter algeriensis genome and recombinantly expressed in Escherichia coli BL21(DE3). The amino acid sequence analysis showed that XynBCA belongs to the glycoside hydrolase family 10. The purified recombinant enzyme has a monomeric structure of 52 kDa. It is active and stable in a wide range of pH from 3 to 10 with a maximum activity at 6.5. Interestingly, XynBCA was highly thermoactive with an optimum temperature of 80 °C, thermostable with a half-life of 20 min at 80 °C. The specific activity was 117 U mg^-1, while the K_m and V_max were 1.247 mg ml^-1, and 114.7 μmol min^-1 mg^-1, respectively. The investigation of XynBCA in kraft pulp biobleaching experiments showed effectiveness in releasing reducing sugars and chromophores, with best achievements at 100 U g^-1 of pulp and 1 h of incubation. The comparative molecular modeling studies with the less thermostable Xylanase B from Clostridium stercorarium, revealed extra charged residues at the surface of XynBCA potentially participating in the formation of intermolecular hydrogen bonds with solvent molecules or generating salt bridges, therefore contributing to the higher thermal stability.

Potential applications of extracellular enzymes from Streptomyces spp. in various industries

Extracellular enzymes produced from Streptomyces have the potential to replace toxic chemicals that are being used in various industries. The endorsement of this replacement has not received a better platform in developing countries. In this review, we have discussed the impact of chemicals and conventional practices on environmental health, and the role of extracellular enzymes to replace these practices. Burning of fossil fuels and agriculture residue is a global issue, but the production of biofuel using extracellular enzymes may be the single key to solve all these issues. We have discussed the replacement of hazardous chemicals with the use of xylanase, cellulase, and pectinase in food industries. In paper industries, delignification was done by the chemical treatment, but xylanase and laccase have the efficient potential to remove the lignin from pulp. In textile industries, the conventional method includes the chemicals which affect the nervous system and other organs. The use of xylanase, cellulase, and pectinase in different processes can give a safe and environment-friendly option to textile industries. Hazardous chemical pesticides can be replaced by the use of chitinase as an insecticide and fungicide in agricultural practices.

Production, characteristics, and biotechnological applications of microbial xylanases

Microbial xylanases have gathered great attention due to their biotechnological potential at industrial scale for many processes. A variety of lignocellulosic materials, such as sugarcane bagasse, rice straw, rice bran, wheat straw, wheat bran, corn cob, and ragi bran, are used for xylanase production which also solved the great issue of solid waste management. Both solid-state and submerged fermentation have been used for xylanase production controlled by various physical and nutritional parameters. Majority of xylanases have optimum pH in the range of 4.0-9.0 with optimum temperature at 30-60 °C. For biochemical, molecular studies and also for successful application in industries, purification and characterization of xylanase have been carried out using various appropriate techniques. Cloning and genetic engineering are used for commercial-level production of xylanase, to meet specific economic viability and industrial needs. Microbial xylanases are used in various biotechnological applications like biofuel production, pulp and paper industry, baking and brewing industry, food and feed industry, and deinking of waste paper. This review describes production, characteristics, and biotechnological applications of microbial xylanases.

A detailed overview of xylanases: an emerging biomolecule for current and future prospective

Xylan is the second most abundant naturally occurring renewable polysaccharide available on earth. It is a complex heteropolysaccharide consisting of different monosaccharides such as l-arabinose, d-galactose, d-mannoses and organic acids such as acetic acid, ferulic acid, glucuronic acid interwoven together with help of glycosidic and ester bonds. The breakdown of xylan is restricted due to its heterogeneous nature and it can be overcome by xylanases which are capable of cleaving the heterogeneous β-1,4-glycoside linkage. Xylanases are abundantly present in nature (e.g., molluscs, insects and microorganisms) and several microorganisms such as bacteria, fungi, yeast, and algae are used extensively for its production. Microbial xylanases show varying substrate specificities and biochemical properties which makes it suitable for various applications in industrial and biotechnological sectors. The suitability of xylanases for its application in food and feed, paper and pulp, textile, pharmaceuticals, and lignocellulosic biorefinery has led to an increase in demand of xylanases globally. The present review gives an insight of using microbial xylanases as an “Emerging Green Tool” along with its current status and future prospective.

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.

Sorghum husk biomass as a potential substrate for production of cellulolytic and xylanolytic enzymes by Nocardiopsis sp. KNU

Nocardiopsis sp. KNU was found to degrade various lignocellulosic waste materials, namely, sorghum husk, sugarcane tops and leaves, wheat straw, and rice husk very efficiently. The strain was found to produce high amounts of cellulase and hemicellulase. Augmentation of cotton seed cake as an organic nitrogen source revealed inductions in activities of endoglucanase, glucoamylase, and xylanase up to 70.03, 447.89, and 275.10 U/ml, respectively. Nonionic surfactant Tween-80 addition was found to enhance the activity of endoglucanase enzyme. Cellulase produced by Nocardiopsis sp. KNU utilizing sorghum husk as a substrate was found to retain its stability in various surfactants up to 90%. The produced enzyme was further tested for saccharification of mild alkali pretreated rice husk. The changes in morphology and functional group were analyzed using scanning electron microscopy and Fourier transform infrared spectroscopy. Enzymatic saccharification confirmed the hydrolytic potential of crude cellulase. The hydrolysate products were analyzed by high-performance thin layer chromatography.

Hot springs of Indian Himalayas: potential sources of microbial diversity and thermostable hydrolytic enzymes

Microbial communities in hot springs at high elevations have been extensively studied worldwide. In this sense, the Indian Himalaya regions is valuable ecosystems for providing both the extreme 'cold' and 'hot' sites for exploring microbial diversity. In the present study, a total of 140 thermophilic bacteria were isolated from 12 samples collected from Manikaran and Yumthang hot springs of Indian Himalayas. The bacterial isolates were studied for phylogenetic profiling, growth properties at varying conditions and potential sources of extracellular thermostable hydrolytic enzymes such as protease, amylase, xylanase and cellulase. Based on production of extracellular hydrolases, 51 isolates from Manikaran (28) and Yumthang thermal springs (23) were selected and identified using 16S rRNA gene sequencing which included 37 distinct species of 14 different genera namely Anoxybacillus, Bacillus, Brevibacillus, Brevundimonas, Burkholderia, Geobacillus, Paenibacillus, Planococcus, Pseudomonas, Rhodanobacter, Thermoactinomyces, Thermobacillus, Thermonema and Thiobacillus. Out of 51 hydrolase producing bacteria, 24 isolates showed stability at wide range of temperature and pH treatments. In present investigation, three thermotolerant bacteria namely, Thermobacillus sp NBM6, Paenibacillus ehimensis NBM24 and Paenibacillus popilliae NBM68 were found to produced cellulase-free xylanase. These potential extracellular thermostable hydrolytic enzymes producing thermophilic bacteria have a great commercial prospect in various industrial, medical and agriculture applications.

Improved efficacy of ultrafiltered xylanase-pectinase concoction in biobleaching of plywood waste soda pulp

The effect of ultrafiltered xylanase–pectinase concoction produced simultaneously by a bacterial isolate using agro-waste-based media was assessed in prebleaching of plywood waste pulp. Ultrafiltered enzymes caused 12.5% reduction in kappa number at reduced enzyme dose of xylanase–pectinase (4.0–0.8 IU) per gram of pulp under optimized conditions at pH 8.5, temperature 55 °C, and treatment period of 2 h. Using this methodology, amount of Cl₂–ClO₂ consumption can be reduced up to 30 and 28.86%. Significant improvement in physical and optical properties of pulp was obtained along with an additional reduction in BOD and COD values up to 18.13 and 21.66% using this novel biodelignification approach. This is the first report showing the advantages of using ultrafiltered xylanase–pectinase over crude enzymes in enhancing the bleaching capacity of pulp. This study focussing on the development of good quality paper with less pollution generating strategy will definitely prove a boon for industries.

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.