Alkali-thermostable and cellulase-free xylanase production by an extreme thermophile Geobacillus thermoleovorans

Optimization and Characterization of an Ultra-Thermostable, Acidophilic, Cellulase-Free Xylanase from a New Obligate Thermophilic Geobacillus thermoleovorans AKNT10 and its Application in Saccharification of Wheat Bran

Microbial xylanases are enzymes of great importance due to their wide industrial applications, especially in the degradation of lignocellulosic biomass into fermentable sugars. This study aimed to describe the production optimization and partial characterization of an ultra-thermostable, acidophilic, cellulase-free xylanase from an obligate thermophilic eubacterium Geobacillus thermoleovorans strain-AKNT10 (Ac.No. LT158229) isolated from a hot-spring of Puga Valley located at an altitude of 4419 m in Ladakh, India. The optimization of cultural conditions improved enzyme yield by 10.49-fold under submerged fermentation. The addition of 1% (w/v) xylose induced the enzyme synthesis by ~ 165 and 371% when supplemented in the fermentation medium containing wheat bran (WB) 1 and 3%, respectively. The supplementation of sucrose reduced the xylanase production by ~ 25%. Results of partial characterization exhibited that xylanase was optimally active at pH 6.0 and 100 °C. Enzyme retained > 75%, > 83%, and > 84% of activity at 4 °C for 28 days, 100 °C for 60 min, and pHs 3-8 for 60 min, respectively. An outstanding property of AKNT10-xylanase, was the retention of > 71% residual activity at extreme conditions (121 °C and 15 psi pressure) for 15 min. Enzymatic saccharification showed that enzyme was also capable to liberate maximum reducing sugars within 4-8 h under optimized conditions thus it could be a potential candidate for the bioconversion of lignocellulosic biomass as well as other industrial purposes. To the best of our knowledge, this is the first report on such an ultra-thermo-pressure-tolerant xylanase optimally active at pH 6 and 100 °C from the genus Geobacillus.

Production Optimization and Biochemical Characterization of Cellulase from Geobacillus sp. KP43 Isolated from Hot Spring Water of Nepal

This study is aimed at isolating and identifying a thermophilic cellulolytic bacterium from hot spring water and characterizing thermostable cellulase produced by the isolate. Enrichment and culture of water sample was used for isolation of bacterial strains and an isolate with highest cellulase activity was chosen for the production, partial purification, and biochemical characterization of the enzyme. Different staining techniques, enzymatic tests, and 16s ribosomal DNA (16s rDNA) gene sequencing were used for the identification of the isolate. The cellulase producing isolate was Gram positive, motile, and sporulated rod-shaped bacterium growing optimally between 55°C and 65°C. Based on partial 16s rDNA sequence analysis, the isolate was identified as Geobacillus sp. and was designated as Geobacillus sp. KP43. The cellulase enzyme production condition was optimized, and the product was partially purified and biochemically characterized. Optimum cellulase production was observed in 1% carboxymethyl cellulose (CMC) at 55°C. The molecular weight of the enzyme was found to be approximately 66 kDa on 12% SDS-PAGE analysis. Biochemical characterization of partially purified enzyme revealed the temperature optimum of 70°C and activity over a wide pH range. Further, cellulase activity was markedly stimulated by metal ion Fe^2+. Apart from cellulases, the isolate also depicted good xylanase, cellobiase, and amylase activities. Thermophilic growth with a variety of extracellular enzyme activities at elevated temperature as well as in a wide pH range showed that the isolated bacteria, Geobacillus sp. KP43, can withstand the harsh environmental condition, which makes this organism suitable for enzyme production for various biotechnological and industrial applications.

Current status and applications of genus Geobacillus in the production of industrially important products-a review

The genus Geobacillus is one of the most important genera which mainly comprises gram-positive thermophilic bacterial strains including obligate aerobes, denitrifiers and facultative anaerobes having capability of endospore formation as well. The genus Geobacillus is widely distributed in nature and mostly abundant in extreme locations such as cool soils, hot springs, hydrothermal vents, marine trenches, hay composts and dairy plants. Due to plasticity towards environmental adaptation, the Geobacillus sp. shows remarkable genome diversification and acquired many beneficial properties, which facilitates their exploitation for many biotechnological applications. Many thermophiles are of biotechnological importance and having considerable interest in commercial applications for the production of industrially important products. Recently, due to catabolic versatility especially in the degradation of hemicellulose and starch containing agricultural waste and rapid growth rates, these microorganisms show potential for the production of biofuels, thermostable enzymes and bioremediation. This review mainly summarizes the status of Geobacillus sp. including its notable properties, biotechnological studies and its potential application in the production of industrially important products.

Overview of lignocellulolytic enzyme systems with special reference to valorization of lignocellulosic biomass

Lignocellulosic biomass, one of the most valuable natural resources, is abundantly present on earth. Being a renewable feedstock, it harbors a great potential to be exploited as a raw material, to produce various value-added products. Lignocellulolytic microorganisms hold a unique position regarding the valorization of lignocellulosic biomass as they contain efficient enzyme systems capable of degrading this biomass. The ubiquitous nature of these microorganisms and their survival under extreme conditions have enabled their use as an effective producer of lignocellulolytic enzymes with improved biochemical features crucial to industrial bioconversion processes. These enzymes can prove to be an exquisite tool when it comes to the eco-friendly manufacturing of value-added products using waste material. This review focuses on highlighting the significance of lignocellulosic biomass, microbial sources of lignocellulolytic enzymes and their use in the formation of useful products.

Isolation, identification, and characterization of lignocellulose-degrading Geobacillus thermoleovorans from Yellowstone National Park

The microbial degradation of lignocellulose in natural ecosystems presents numerous biotechnological opportunities, including biofuel production from agricultural waste and feedstock biomass. To explore the degradation potential of specific thermophiles, we have identified and characterized extremophilic microorganisms isolated from hot springs environments that are capable of biodegrading lignin and cellulose substrates under thermoalkaline conditions, using a combination of culturing, genomics and metabolomics techniques. Organisms that can use lignin and cellulose as a sole carbon source at 60-75°C were isolated from sediment slurry of thermoalkaline hot springs (71-81°C and pH 8-9) of Yellowstone National Park. Full-length 16S rRNA gene sequencing indicated that these isolates were closely related to Geobacillus thermoleovorans. Interestingly, most of these isolates demonstrated biofilm formation on lignin, a phenotype that is correlated with increased bioconversion. Assessment of metabolite level changes in two Geobacillus isolates from two representative springs were undertaken to characterize the metabolic responses associated with growth on glucose versus lignin carbon source as a function of pH and temperature. Overall, results from this study support that thermoalkaline springs harbor G. thermoleovorans microorganisms with lignocellulosic biomass degradation capabilities and potential downstream biotechnological applications. IMPORTANCE As lignocellulosic biomass represents a major agro-industrial waste and renewable resource, its potential to replace non-renewable petroleum-based products for energy production is considerable. Microbial ligninolytic and cellulolytic enzymes are of high interest in bio-refineries for the valorization of lignocellulosic biomass, as they can withstand the extreme conditions (e.g., high temperature, high pH) required for processing. Of high interest is the ligninolytic potential of specific Geobacillus thermoleovorans isolates to function at a broad range of pH and temperatures, as lignin is the bottleneck in the bioprocessing of lignocellulose. In this study, results obtain from G. thermolerovorans isolates originating from YNP springs are significant as very few microorganisms from alkaline thermal environments have been discovered to have lignin and cellulose biodegrading capabilities, and this work opens new avenues for the biotechnological valorization of lignocellulosic biomass at an industrial scale.

Extremophilic Prokaryotic Endoxylanases: Diversity, Applicability, and Molecular Insights

Extremophilic endoxylanases grabbed attention in recent years due to their applicability under harsh conditions of several industrial processes. Thermophilic, alkaliphilic, and acidophilic endoxylanases found their employability in bio-bleaching of paper pulp, bioconversion of lignocellulosic biomass into xylooligosaccharides, bioethanol production, and improving the nutritious value of bread and other bakery products. Xylanases obtained from extremophilic bacteria and archaea are considered better than fungal sources for several reasons. For example, enzymatic activity under broad pH and temperature range, low molecular weight, cellulase-free activity, and longer stability under extreme conditions of prokaryotic derived xylanases make them a good choice. In addition, a short life span, easy cultivation/harvesting methods, higher yield, and rapid DNA manipulations of bacterial and archaeal cells further reduces the overall cost of the product. This review focuses on the diversity of prokaryotic endoxylanases, their characteristics, and their functional attributes. Besides, the molecular mechanisms of their extreme behavior have also been presented here.

Paecilomyces variotii xylanase production, purification and characterization with antioxidant xylo-oligosaccharides production

Paecilomyces variotii xylanase was, produced in stirred tank bioreactor with yield of 760 U/mL and purified using 70% ammonium sulfate precipitation and ultra-filtration causing 3.29-fold purification with 34.47% activity recovery. The enzyme purity was analyzed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirming its monomeric nature as single band at 32 KDa. Zymography showed xylan hydrolysis activity at the same band. The purified enzyme had optimum activity at 60 °C and pH 5.0. The pH stability range was 5-9 and the temperature stability was up 70 °C. Fe²⁺and Fe³⁺ exhibited inhibition of xylanase enzyme while Cu²⁺, Ca²⁺, Mg²⁺ and Mn²⁺ stimulated its activity. Mercaptoethanol stimulated its activity; however, Na₂-EDTA and SDS inhibited its activity. The purified xylanase could hydrolyze beechwood xylan but not carboxymethyl cellulose (CMC), avicel or soluble starch. Paecilomyces variotii xylanase K_m and V_max for beechwood were determined to be 3.33 mg/mL and 5555 U/mg, respectively. The produced xylanase enzyme applied on beech xylan resulted in different types of XOS. The antioxidant activity of xylo-oligosaccharides increased from 15.22 to 70.57% when the extract concentration was increased from 0.1 to 1.5 mg/mL. The enzyme characteristics and kinetic parameters indicated its high efficiency in the hydrolysis of xylan and its potential effectiveness in lignocellulosic hydrolysis and other industrial application. It also suggests the potential of xylanase enzyme for production of XOS from biomass which are useful in food and pharmaceutical industries.

Computational approach for identification, characterization, three-dimensional structure modelling and machine learning-based thermostability prediction of xylanases from the genome of Aspergillus fumigatus

Identification of thermostable and alkaline xylanases from different fungal and bacterial species have gained an interest for the researchers because of its biotechnological relevance in many industries, such as pulp, paper, and bioethanol. In this study, we have identified and characterized xylanases from the genome of the thermophilic fungus of Aspergillus fumigatus by in silico analysis. Genome data mining revealed that the A fumigatus genome has six xylanase genes that belong to GH10, GH11, GH43 glycoside hydrolase families. In general, most of the bacterial and fungal GH11 xylanases are alkaline, and GH10 xylanases are acidic; however, we found that one identified xylanase from A fumigatus that belongs to the GH10 family is alkaline while the rest are acidic. Moreover, physicochemical properties also stated that most of the xylanases identified have lower molecular weight except one that belongs to the GH43 family. Structure prediction by homology modelling gave optimized structures of the xylanases. It suggests that GH10 family structure models adapt (β∕α) 8 barrel type, GH11 homology models adapt β-jelly type, and the GH43 family has a fivefold β-propeller type structure. Molecular docking of identified xylanases with xylan revealed that GH11 xylanases have strong interaction (-9.6 kcal/mol) with xylan than the GH10 (-8.5 and -9.3 kcal/mol) and GH43 (-8.8 kcal/mol). We used the machine learning approach based TAXyl server to predict the thermostability of the xylanases. It revealed that two GH10 xylanases and one GH11 xylanase are thermo-active up to 75ᵒC. We have explored the physiochemical properties responsible for maintaining thermostability for bacterial and fungal GH10 and GH11 xylanases by comparing crystal structures. All the analyzed parameters specified that GH10 xylanases from both the fungi and bacteria are more thermostable due to higher hydrogen bonds, salt bridges, and helical content.

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.

Xylanolytic Extremozymes Retrieved From Environmental Metagenomes: Characteristics, Genetic Engineering, and Applications

Xylanolytic enzymes have extensive applications in paper, food, and feed, pharmaceutical, and biofuel industries. These industries demand xylanases that are functional under extreme conditions, such as high temperature, acidic/alkaline pH, and others, which are prevailing in bioprocessing industries. Despite the availability of several xylan-hydrolyzing enzymes from cultured microbes, there is a huge gap between what is available and what industries require. DNA manipulations as well as protein-engineering techniques are also not quite satisfactory in generating xylan-hydrolyzing extremozymes. With a compound annual growth rate of 6.6% of xylan-hydrolyzing enzymes in the global market, there is a need for xylanolytic extremozymes. Therefore, metagenomic approaches have been employed to uncover hidden xylanolytic genes that were earlier inaccessible in culture-dependent approaches. Appreciable success has been achieved in retrieving several unusual xylanolytic enzymes with novel and desirable characteristics from different extreme environments using functional and sequence-based metagenomic approaches. Moreover, the Carbohydrate Active Enzymes database includes approximately 400 GH-10 and GH-11 unclassified xylanases. This review discusses sources, characteristics, and applications of xylanolytic enzymes obtained through metagenomic approaches and their amelioration by genetic engineering techniques.

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.

Comprehensive studies on optimization of cellulase and xylanase production by a local indigenous fungus strain via solid state fermentation using oil palm frond as substrate

The high cost of cellulases remains the most significant barrier to the economical production of bio-ethanol from lignocellulosic biomass. The goal of this study was to optimize cellulases and xylanase production by a local indigenous fungus strain (Aspergillus niger DWA8) using agricultural waste (oil palm frond [OPF]) as substrate. The enzyme production profile before optimization indicated that the highest carboxymethyl cellulose (CMCase), filter paper (FPase), and xylanase activities of 1.06 U/g, 2.55 U/g, and 2.93 U/g were obtained on day 5, day 4, and day 5 of fermentation, respectively. Response surface methodology was used to study the effects of several key process parameters in order to optimize cellulase production. Of the five physical and two chemical factors tested, only moisture content of 75% (w/w) and substrate amount of 2.5 g had statistically significant effect on enzymes production. Under optimized conditions of 2.5 g of substrate, 75% (w/w) moisture content, initial medium of pH 4.5, 1 × 10⁶ spores/mL of inoculum, and incubation at ambient temperature (±30°C) without additional carbon and nitrogen, the highest CMCase, FPase, and xylanase activities obtained were 2.38 U/g, 2.47 U/g, and 5.23 U/g, respectively. Thus, the optimization process increased CMCase and xylanase production by 124.5 and 78.5%, respectively. Moreover, A. niger DWA8 produced reasonably good cellulase and xylanase titers using OPF as the substrate when compared with previous researcher finding. The enzymes produced by this process could be further use to hydrolyze biomass to generate reducing sugars, which are the feedstock for bioethanol production.

Alkaline Active Hemicellulases

Xylan and mannan are the two most abundant hemicelluloses, and enzymes that modify these polysaccharides are prominent hemicellulases with immense biotechnological importance. Among these enzymes, xylanases and mannanases which play the vital role in the hydrolysis of xylan and mannan, respectively, attracted a great deal of interest. These hemicellulases have got applications in food, feed, bioethanol, pulp and paper, chemical, and beverage producing industries as well as in biorefineries and environmental biotechnology. The great majority of the enzymes used in these applications are optimally active in mildly acidic to neutral range. However, in recent years, alkaline active enzymes have also become increasingly important. This is mainly due to some benefits of utilizing alkaline active hemicellulases over that of neutral or acid active enzymes. One of the advantages is that the alkaline active enzymes are most suitable to applications that require high pH such as Kraft pulp delignification, detergent formulation, and cotton bioscouring. The other benefit is related to the better solubility of hemicelluloses at high pH. Since the efficiency of enzymatic hydrolysis is often positively correlated to substrate solubility, the hydrolysis of hemicelluloses can be more efficient if performed at high pH. High pH hydrolysis requires the use of alkaline active enzymes. Moreover, alkaline extraction is the most common hemicellulose extraction method, and direct hydrolysis of the alkali-extracted hemicellulose could be of great interest in the valorization of hemicellulose. Direct hydrolysis avoids the time-consuming extensive washing, and neutralization processes required if non-alkaline active enzymes are opted to be used. Furthermore, most alkaline active enzymes are relatively active in a wide range of pH, and at least some of them are significantly or even optimally active in slightly acidic to neutral pH range. Such enzymes can be eligible for non-alkaline applications such as in feed, food, and beverage industries.This chapter largely focuses on the most important alkaline active hemicellulases, endo-β-1,4-xylanases and β-mannanases. It summarizes the relevant catalytic properties, structural features, as well as the real and potential applications of these remarkable hemicellulases in textile, paper and pulp, detergent, feed, food, and prebiotic producing industries. In addition, the chapter depicts the role of these extremozymes in valorization of hemicelluloses to platform chemicals and alike in biorefineries. It also reviews hemicelluloses and discusses their biotechnological importance.

Thermostable Xylanase Production by Geobacillus sp. Strain DUSELR13, and Its Application in Ethanol Production with Lignocellulosic Biomass

The aim of the current study was to optimize the production of xylanase, and its application for ethanol production using the lignocellulosic biomass. A highly thermostable crude xylanase was obtained from the Geobacillus sp. strain DUSELR13 isolated from the deep biosphere of Homestake gold mine, Lead, SD. Geobacillus sp. strain DUSELR13 produced 6 U/mL of the xylanase with the beechwood xylan. The xylanase production was improved following the optimization studies, with one factor at a time approach, from 6 U/mL to 19.8 U/mL with xylan. The statistical optimization with response surface methodology further increased the production to 31 U/mL. The characterization studies revealed that the crude xylanase complex had an optimum pH of 7.0, with a broad pH range of 5.0⁻9.0, and an optimum temperature of 75 °C. The ~45 kDa xylanase protein was highly thermostable with t_1/2 of 48, 38, and 13 days at 50, 60, and 70 °C, respectively. The xylanase activity increased with the addition of Cu^+2, Zn⁺², K^+, and Fe⁺² at 1 mM concentration, and Ca⁺², Zn⁺², Mg⁺², and Na⁺ at 10 mM concentration. The comparative analysis of the crude xylanase against its commercial counterpart Novozymes Cellic HTec and Dupont, Accellerase XY, showed that it performed better at higher temperature, hydrolyzing 65.4% of the beechwood at 75 °C. The DUSEL R13 showed the mettle to hydrolyze, and utilize the pretreated, and untreated lignocellulosic biomass: prairie cord grass (PCG), and corn stover (CS) as the substrate, and gave a maximum yield of 20.5 U/mL with the untreated PCG. When grown in co-culture with Geobacillus thermoglucosidasius, it produced 3.53 and 3.72 g/L ethanol, respectively with PCG, and CS. With these characteristics the xylanase under study could be an industrial success for the high temperature bioprocesses.

Effect of disulfide bridge on hydrolytic characteristics of xylanase from Penicillium janthinellum

Highly efficient and stable enzymes are required for application in biotechnology, to meet the technical, environmental, and economic industrial demands. Xylanases are hemicellulolytic enzymes that degrade the heteroxylan constituent of the lignocellulosic plant cell wall. In this study, an acidic xylanase designated Pjxyn (pH 4.0) from Penicillium janthinellum was engineered by the introduction of a disulfide bridge. This strategy exploited the influence of the bridge on hydrolysis characteristics and enhanced hydrolysis was achieved. Three mutants [PjxynS(27)S(39), PjxynS(27)S(186), and PjxynS(39)S(186)] produced more xylose and xylobiose as hydrolysis products compared with the wild-type Pjxyn, when commercial xylans and lab-prepared water-insoluble corncob-xylan were used as the substrates, especial for the PjxynS(27)S(39) mutant, the content of xylose and xylobiose was 87.62% (using beechwood xylan) and 69.91% (using oat-spelt xylan) higher than that in the hydrolysis products of Pjxyn. Moreover, each mutant combined with the xylanase mutant T-XynFM effectively decreased the production of xylose with an optimum xylobiose yield. The findings demonstrate the potential industrial value of engineering xylanase to improve its hydrolytic properties and thermostability.

Effect of CBM1 and linker region on enzymatic properties of a novel thermostable dimeric GH10 xylanase (Xyn10A) from filamentous fungus Aspergillus fumigatus Z5

Xylanase with a high thermostability will satisfy the needs of raising the temperature of hydrolysis to improve the rheology of the broth in industry of biomass conversion. In this study, a xylanase gene (xyn10A), predicted to encode a hydrolase domain of GH10, a linker region and a CBM1 domain, was cloned from a superior lignocellulose degrading strain Aspergillus fumigatus Z5 and successfully expressed in Pichia pastoris X33. Xyn10A has a specific xylanase activity of 34.4 U mg⁻¹, and is optimally active at 90 °C and pH 6.0. Xyn10A shows quite stable at pHs ranging from 3.0 to 11.0, and keeps over 40% of xylanase activity after incubation at 70 °C for 1 h. Removal of CBM1 domain has a slight negative effect on its thermostability, but the further cleavage of linker region significantly decreased its stability at high temperature. The transfer of CBM1 and linker region to another GH10 xylanase can help to increase the thermostability. In addition, hydrolase domains between the two Xyn10A proteins naturally formed a dimer structure, which became more thermostable after removing the CBM1 or/and linker region. This thermostable Xyn10A is a suitable candidate for the highly efficient fungal enzyme cocktails for biomass conversion.

Characterization of Cellulolytic and Xylanolytic Enzymes of Bacillus licheniformis JK7 Isolated from the Rumen of a Native Korean Goat

A facultative bacterium producing cellulolytic and hemicellulolytic enzymes was isolated from the rumen of a native Korean goat. The bacterium was identified as a Bacillus licheniformis on the basis of biochemical and morphological characteristics and 16S rDNA sequences, and has been designated Bacillus licheniformis JK7. Endoglucanase activities were higher than those of β-glucosidase and xylanase at all temperatures. Xylanase had the lowest activity among the three enzymes examined. The optimum temperature for the enzymes of Bacillus licheniformis JK7 was 70°C for endoglucanase (0.75 U/ml) and 50°C for β-glucosidase and xylanase (0.63 U/ml, 0.44 U/ml, respectively). All three enzymes were stable at a temperature range of 20 to 50°C. At 50°C, endoglucanse, β-glucosidase, and xylanase had 90.29, 94.80, and 88.69% residual activity, respectively. The optimal pH for the three enzymes was 5.0, at which their activity was 1.46, 1.10, and 1.08 U/ml, respectively. The activity of all three enzymes was stable in the pH range of 3.0 to 6.0. Endoglucanase activity was increased 113% by K⁺, while K⁺, Zn⁺, and tween 20 enhanced β-glucosidase activity. Xylanase showed considerable activity even in presence of selected chemical additives, with the exception of Mn²⁺ and Cu²⁺. The broad range of optimum temperatures (20 to 40°C) and the stability under acidic pH (4 to 6) suggest that the cellulolytic enzymes of Bacillus licheniformis JK7 may be good candidates for use in the biofuel industry.

A Highly Thermostable Xylanase from Stenotrophomonas maltophilia: Purification and Partial Characterization

Seven xylanolytic bacterial strains were isolated from saw-dust dump soil. The bacterial strain X6 was selected on the basis of the highest xylanase activity with no cellulase contamination. It was identified as Stenotrophomonas maltophilia by biochemical tests and 16S rRNA gene sequencing approach. Xylanase production studies by S. maltophilia on different commercial xylans and agro-industrial residues suggested that wheat bran was the best carbon source for xylanase production (26.4 ± 0.6 IU/mL). The studies with inorganic and organic nitrogen sources suggested yeast extract as the best support for xylanase production (25 ± 0.6 IU/mL). Maximum xylanase production was observed at initial medium pH = 8.0 (23.8 ± 0.4 IU/mL) with production at pH = 7.0 and pH = 9.0 being almost comparable. Xylanase produced by S. maltophilia was purified to homogeneity using ammonium sulfate precipitation, gel filtration, and ion exchange chromatography. The final purification was 5.43-fold with recovery of 19.18%. The molecular weight of the purified xylanase protein was ~142 kDa. Both crude and purified xylanase had good stability at pH = 9.0 and 80°C with activity retention greater than 90% after 30 min incubation. The enzyme stability at high temperature and alkaline pH make it potentially effective for industrial applications.

Characterization of a new Providencia sp. strain X1 producing multiple xylanases on wheat bran

Providencia sp. strain X1 showing the highest xylanase activity among six bacterial isolates was isolated from saw-dust decomposing site. Strain X1 produced cellulase-free extracellular xylanase, which was higher in wheat bran medium than in xylan medium, when cultivated at pH 8.0 and 35°C. Zymogram analysis of crude preparation of enzymes obtained while growing on wheat bran and birchwood xylan revealed the presence of seven and two distinct xylanases with estimated molecular weight of 33; 35; 40; 48; 60; 75; and 95 kDa and 33 and 44 kDa, respectively. The crude xylanases were produced on wheat bran medium and showed optimum activity at pH 9.0 and 60°C. The thermotolerance studies showed activity retention of 100% and 85% at 40°C and 60°C after 30 min preincubation at pH 9.0. It was tolerant to lignin, ferulic acid, syringic acid, and guaiacol and retained 90% activity after ethanol treatment. The enzyme preparation was also tolerant to methanol and acetone and showed good activity retention in the presence of metal ions such as Fe²⁺, Mg²⁺, Zn²⁺, and Ca²⁺. The crude enzyme preparation was classified as endoxylanase based on the product pattern of xylan hydrolysis. Pretreatment of kraft pulp with crude xylanases for 3 h at 60°C led to a decrease in kappa number by 28.5%. The properties of present xylanases make them potentially useful for industrial applications.

Production of cellulase-free xylanase by the recombinant Bacillus subtilis and its applicability in paper pulp bleaching

A metagenomic xylanase gene (Mxyl) was successfully cloned into shuttle vector pWH1520 and expressed in Bacillus subtilis extracellularly. On induction with xylose, recombinant xylanase secretion commenced after 6 h. Identifying critical variables for recombinant xylanase production by one-variable-at-time approach followed by optimization of the selected variables (xylose, inoculum density, incubation density) by response surface methodology (RSM) led to three-fold enhancement in extracellular xylanase production (119 U mL(-1) ). When the pulp was treated with recombinant xylanase at 80°C and pH 9.0, kappa number of the pulp was reduced with concomitant increase in brightness and 24% reduction in chlorine consumption. This is the first report on the expression of metagenomic xylanase gene in Bacillus subtilis extracellularly and its utility in developing an environment-friendly pulp bleaching process.

Improvement in thermostability of metagenomic GH11 endoxylanase (Mxyl) by site-directed mutagenesis and its applicability in paper pulp bleaching process

An attempt has been made for enhancing the thermostability of xylanase (Mxyl) retrieved from a compost-soil-based metagenomic library. The analysis of the structure of xylanase by molecular dynamics simulation revealed more structural fluctuations in β-sheets. When the surface of β-sheets was enriched with arginine residues by substituting serine/threonine by site-directed mutagenesis, the enzyme with four arginine substitutions (MxylM4) exhibited enhanced thermostability at 80 °C. The T 1/2 of MxylM4 at 80 °C, in the presence of birchwood xylan, increased from 130 to 150 min at 80 °C without any alteration in optimum pH and temperature and molecular mass. Improvement in thermostability of MxylM4 was corroborated by increase in T m by 6 °C over that of Mxyl. The K m of MxylM4, however, increased from 8.01 ± 0.56 of Mxyl to 12.5 ± 0.32 mg ml(-1), suggesting a decrease in the affinity as well as specific enzyme activity. The Mxyl as well as MxylM4 liberated chromophores and lignin-derived compounds from kraft pulp, indicating their applicability in pulp bleaching.

Cloning, expression and characteristics of a novel alkalistable and thermostable xylanase encoding gene (Mxyl) retrieved from compost-soil metagenome

Background

The alkalistable and thermostable xylanases are in high demand for pulp bleaching in paper industry and generating xylooligosaccharides by hydrolyzing xylan component of agro-residues. The compost-soil samples, one of the hot environments, are expected to be a rich source of microbes with thermostable enzymes.

Methodology/Principal Findings

Metagenomic DNA from hot environmental samples could be a rich source of novel biocatalysts. While screening metagenomic library constructed from DNA extracted from the compost-soil in the p18GFP vector, a clone (TSDV-MX1) was detected that exhibited clear zone of xylan hydrolysis on RBB xylan plate. The sequencing of 6.321 kb DNA insert and its BLAST analysis detected the presence of xylanase gene that comprised 1077 bp. The deduced protein sequence (358 amino acids) displayed homology with glycosyl hydrolase (GH) family 11 xylanases. The gene was subcloned into pET28a vector and expressed in E. coli BL21 (DE3). The recombinant xylanase (rMxyl) exhibited activity over a broad range of pH and temperature with optima at pH 9.0 and 80°C. The recombinant xylanase is highly thermostable having T1/2 of 2 h at 80°C and 15 min at 90°C.

Conclusion/Significance

This is the first report on the retrieval of xylanase gene through metagenomic approach that encodes an enzyme with alkalistability and thermostability. The recombinant xylanase has a potential application in paper and pulp industry in pulp bleaching and generating xylooligosaccharides from the abundantly available agro-residues.

Thermostable and Alkalistable Xylanases Produced by the Thermophilic Bacterium Anoxybacillus flavithermus TWXYL3

With the rising cost and finite supply of fossil energy, there is an increasing economic incentive for the development of clean, efficient, and renewable domestic energy. The activities of microorganisms offer the potential conversion of lignocellulosic materials into fermentable sugars, usable for downstream fermentation processes. Strain TWXYL3, a thermophilic facultative anaerobe, was discovered in the Alvord Basin hydrothermal system in Oregon, USA. Phylogenetic analysis of strain TWXYL3 showed it to be 99% similar to the 16S rRNA gene of Anoxybacillus flavithermus WL (FJ950739). A. flavithermus TWXYL3 was shown to secrete a large multisubunit thermostable xylanase complex into the growth medium. Xylanase induction was achieved by resuspending the isolate in a selective xylan-containing medium. Extracellular xylanase activity showed a temperature optimum of 65°C and retained thermostability up to 85°C. Extracellular xylanase activity showed a bimodal pH optimum, with maxima at pH 6 and pH 8. Electrophoretic analysis of the extracellular xylanase shows 5 distinct proteins with xylanase activity. Strain TWXYL3 is the first xylanolytic isolate obtained from the Alvord Basin hydrothermal system and represents a new model system for development of processes where lignocellulosics are converted to biofuel precursors.

Molecular approaches for ameliorating microbial xylanases

In industrial processes, chemical catalysis is being replaced by enzyme catalysis, since the latter is environmentally benign, non-persistent and cost effective. Microbial xylanases have significant applications in textile, baking, food and feed industries, and in paper and pulp industries for reducing the chlorine requirement. The hazardous chlorine required for bleaching can be reduced up to 25-30% by including an enzymatic step in the pulp bleaching process. The paper pulp bleaching requires xylanases that are active at alkaline pH and elevated temperatures. The enzymes from the cultured microbes do not perform optimally in the paper industry due to their inadequate stability under the process conditions of high temperature and alkaline pH. This review, therefore, deals with the rationale of molecular approaches such as protein engineering for designing xylanases with improved characteristics to suit the process conditions in industries, and prospects and problems.

Cloning, expression and applicability of thermo-alkali-stable xylanase of Geobacillus thermoleovorans in generating xylooligosaccharides from agro-residues

A xylanase gene (xyl-gt) of 1.224 kbp was cloned from the extremely thermophilic bacterium Geobacillus thermoleovorans that encodes a protein containing 408 amino acid residues. Eight conserved regions (signature sequences) of GH family 10 xylanases have been found in the xylanase. When the xylanase gene was cloned and expressed in Escherichia coli BL21 (DE3), the recombinant strain produced xylanase titer of 270 U mg(-1) which is 27-fold higher than the wild strain. It is optimally active at 80°C and pH 8.5 with a high thermostability over broad range of pH (6-12) and temperature (40-100°C). The end products of the hydrolysis of birch wood xylan and agro-residues included xylobiose, xylotriose, xylotetraose and xylopentaose. The xylanase of G. thermoleovorans is one of the rare xylanases that exhibits thermo-alkali-stability, and thus, it is a suitable candidate for pre-bleaching of paper pulps and generating xylooligosaccharides from agro-residues for use as prebiotics.

Production of xylanase under solid-state fermentation by Aspergillus tubingensis JP-1 and its application

The production of extracellular xylanase by a locally isolated strain of Aspergillus tubingensis JP-1 was studied under solid-state fermentation. Among the various agro residues used wheat straw was found to be the best for high yield of xylanase with poor cellulase production. The influence of various parameters such as initial pH, moisture, moistening agents, nitrogen sources, additives, surfactants and pretreatment of substrates were investigated. The production of the xylanase reached a peak in 8 days using untreated wheat straw with modified MS medium, pH 6.0 at 1:5 moisture level at 30 °C. Under optimized conditions yield as high as 6,887 ± 16 U/g of untreated wheat straw was achieved. Crude xylanase was used for enzymatic saccharification of agro-residues like wheat straw, rice bran, wheat bran, sugarcane bagasse and industrial paper pulp. Dilute alkali (1 N NaOH) and acid (1 N H(2)SO(4)) pretreatment were found to be beneficial for the efficient enzymatic hydrolysis of wheat straw. Dilute alkali and acid-pretreated wheat straw yielded 688 and 543 mg/g reducing sugar, respectively. Yield of 726 mg/g reducing sugar was obtained from paper pulp after 48 h of incubation.

Production of alkali tolerant cellulase free xylanase in high levels by Bacillus pumilus SV-205

The fermentation conditions were optimized for hyper production of xylanase from Bacillus pumilus SV-205. The bacterium secretes high levels (7382.7±1200 IU/mL) of cellulase-free xylanase using wheat bran led to 21.63 fold increase in activity. A combination of yeast extract and peptone stimulated highest xylanase production (2448.0 IU/mL) as compared to other combinations. The most important characteristic of the enzyme is its high pH stability (100%) over a broad pH range of 6-11 for 24h. Thermostability studies revealed that enzyme retained 65% activity after an incubation of 2h at 60°C. The level of production is remarkable as compared to earlier reports.

Production and optimization of cellulase-free, alkali-stable xylanase by Bacillus pumilus SV-85S in submerged fermentation

This paper reports the production of a cellulase-free and alkali-stable xylanase in high titre from a newly isolated Bacillus pumilus SV-85S using cheap and easily available agro-residue wheat bran. Optimization of fermentation conditions enhanced the enzyme production to 2995.20 +/- 200.00 IU/ml, which was 9.91-fold higher than the activity under unoptimized basal medium (302.2 IU/ml). Statistical optimization using response-surface methodology was employed to obtain a cumulative effect of peptone, yeast extract, and potassium nitrate (KNO(3)) on enzyme production. A 2(3) central composite design best optimized the nitrogen source at the 0 level for peptone and yeast extract and at the -alpha level for KNO(3), along with 5.38-fold increase in xylanase activity. Addition of 0.1% tween 80 to the medium increased production by 1.5-fold. Optimum pH for xylanase was 6.0. The enzyme was 100% stable over the pH range from 5 to 11 for 1 h at 37 degrees C and it lost no activity, even after 3 h of incubation at pH 7, 8, and 9. Optimum temperature for the enzyme was 50 degrees C, but the enzyme displayed 78% residual activity even at 65 degrees C. The enzyme retained 50% activity after an incubation of 1 h at 60 degrees C. Characteristics of B. pumilus SV-85S xylanase, including its cellulase-free nature, stability in alkali over a long duration, along with high-level production, are particularly suited to the paper and pulp industry.

A novel endo-glucanase from the thermophilic bacterium Geobacillus sp. 70PC53 with high activity and stability over a broad range of temperatures

A thermophilic Geobacillus bacterium secreting high activity of endo-glucanase (EC 3.2.1.4) was isolated from rice straw compost supplemented with pig manure. A full-length gene of 1,104 bp, celA, encoding this glycosyl hydrolase family 5 endo-glucanase of 368 amino acids was isolated. No related gene from Geobacillus has been reported previously. The recombinant CelA expressed in Escherichia coli had an optimal activity at 65 degrees C and pH 5.0, and it exhibited tenfold greater specific activity than the commercially available Trichoderma reesei endo-glucanase. CelA displayed activity over a broad temperature range from 45 to 75 degrees C and was a thermostable enzyme with 90% activity retained after heating at 65 degrees C for 6 h. Interestingly, CelA activity could be enhanced by 100% in the presence of 2 mM MnSO(4). CelA had high specific activity over beta-D-glucan from barley and Lichenan, making it a potentially useful enzyme in biofuel and food industries.