Applicability of thermo-alkali-stable and cellulase-free xylanase from a novel thermo-halo-alkaliphilic Bacillus halodurans in producing xylooligosaccharides

Engineering of xylanases for the development of biotechnologically important characteristics

Xylanases are the main biocatalysts used for the reduction of the xylan backbone from hemicellulose, randomly splitting off β-1,4-glycosidic linkages between xylopyranosyl residues. Xylanase market has been annually estimated at 500 million US Dollars and they are potentially used in broad industrial process ranges such as paper pulp biobleaching, xylo-oligosaccharide production, and biofuel manufacture from lignocellulose. The highly stable xylanases are preferred in the downstream procedure of industrial processes because they can tolerate severe conditions. Almost all native xylanases can not endure adverse conditions thus they are industrially not proper to be utilized. Protein engineering is a powerful technology for developing xylanases, which can effectively work in adverse conditions and can meet requirements for industrial processes. This study considered state-of-the-art strategies of protein engineering for creating the xylanase gene diversity, high-throughput screening systems toward upgraded traits of the xylanases, and the prediction and comprehensive analysis of the target mutations in xylanases by in silico methods. Also, key molecular factors have been elucidated for industrial characteristics (alkaliphilic enhancement, thermal stability, and catalytic performance) of GH11 family xylanases. The present review explores industrial characteristics improved by directed evolution, rational design, and semi-rational design as protein engineering approaches for pulp bleaching process, xylooligosaccharides production, and biorefinery & bioenergy production.

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.

Purification and characterization of a highly-stable fungal xylanase from Aspergillus tubingensis cultivated on palm wastes through combined solid-state and submerged fermentation

Fungal xylanase was produced from lignocellulosic palm wastes through combined solid-state fermentation (SSF) and submerged fermentation (SmF) by Aspergillus tubingensis TSIP9 in a helical-impeller equipped bioreactor. The combined SSF-SmF promoted the xylanase production by 15 and 70% higher than SSF and SmF, respectively. Sequential purification yielded 7.4-fold purified xylanase with 9.07% recovery. The maximum activities of crude and purified xylanase were observed at the same pH of 5.0 and the same temperature of 50 °C while purified xylanase is more active and highly stable at a wider pH range of 3-8 and temperature of 30-60 °C. The half-life of purified xylanase at various temperatures was also much improved by 2-8 folds compared to crude xylanase. Michaelis-Menten constants, V_max and K_m, for purified xylanase are 2,602.8 U/mg and 32.4 mg/mL, respectively. Purified xylanase activity was most enhanced with Ca²⁺ followed by Zn²⁺ and Fe²⁺ at 10 mM while significantly inhibited by Co²⁺, Cu²⁺, Pb²⁺, and Ag⁺. This study has shown the effectiveness of combined SSF-SmF for xylanase production and superior properties of purified xylanase for industrial processes.

Novel and emerging prebiotics: Advances and opportunities

Consumers are conscientiously changing their eating preferences toward healthier options, such as functional foods enriched with pre- and probiotics. Prebiotics are attractive bioactive compounds with multidimensional beneficial action on both human and animal health, namely on the gastrointestinal tract, cardiometabolism, bones or mental health. Conventionally, prebiotics are non-digestible carbohydrates which generally present favorable organoleptic properties, temperature and acidic stability, and are considered interesting food ingredients. However, according to the current definition of prebiotics, application categories other than food are accepted, as well as non-carbohydrate substrates and bioactivity at extra-intestinal sites. Regulatory issues are considered a major concern for prebiotics since a clear understanding and application of these compounds among the consumers, regulators, scientists, suppliers or manufacturers, health-care providers and standards or recommendation-setting organizations are of utmost importance. Prebiotics can be divided in several categories according to their development and regulatory status. Inulin, galactooligosaccharides, fructooligosaccharides and lactulose are generally classified as well established prebiotics. Xylooligosaccharides, isomaltooligosaccharides, chitooligosaccharides and lactosucrose are classified as "emerging" prebiotics, while raffinose, neoagaro-oligosaccharides and epilactose are "under development." Other substances, such as human milk oligosaccharides, polyphenols, polyunsaturated fatty acids, proteins, protein hydrolysates and peptides are considered "new candidates." This chapter will encompass actual information about the non-established prebiotics, mainly their physicochemical properties, market, legislation, biological activity and possible applications. Generally, there is a lack of clear demonstrations about the effective health benefits associated with all the non-established prebiotics. Overcoming this limitation will undoubtedly increase the demand for these compounds and their market size will follow the consumer's trend.

Bioprocessing of waste biomass for sustainable product development and minimizing environmental impact

Growing concerns around the generation of biomass waste have triggered conversation around sustainable utilization of these seemingly waste materials as feedstock towards energy generation and production of chemicals and other value-added products. Thus, biotechniques such as utilization of microbes and enzymes derived thereof have become important avenues for green pretreatment and conversion of biomass wastes. Although the products of these bioconversions are greener at an overall level, their consumption and utilization still impact the environment. Hence it is important to understand the overall impact from cradle to grave through lifecycle assessment (LCA) techniques and find avenues of process optimization and better utilization of all the materials and products involved. Another factor to consider is overall cost optimization to make the process economically feasible, profitable and increase industrial adoption. This review brings forward these critical aspects to provide better understanding for the advancement of bioeconomy.

Enhancement of catalytic performance of a metagenome-derived thermophilic oligosaccharide-specific xylanase by binding module removal and random mutagenesis

Xylo-oligosaccharide (XO) is a promising pre-biotic with applications in food, feed and healthcare products. XO can be produced by enzymatic digestion of xylan with xylanase. In this study, we aimed to improve the biochemical properties relevant to catalysis and kinetics of X11, a thermophilic glycosyl hydrolase (GH) family 11 endo-β-1,4-xylanase derived from a metagenomic library isolated from sugarcane bagasse, under high-temperature conditions preferred for XO synthesis. Removal of a carbohydrate-binding module (X11C) resulted in 6.5 fold greater catalytic efficiency. X11C was further improved by a Pro71Thr mutation in the X11P variant obtained from a random mutagenesis library, which exhibited 15.9 fold greater catalytic efficiency compared with wild-type X11 under the enzyme's optimal conditions of 80°C and pH 6.0. Homology modeling suggested that the improved performance of X11P could be attributed to formation of an extra H-bond between Thr71 and Ser75, which stabilizes the key catalytic residue Glu180 at the active pocket and β-sheet layers and agrees with the respective increase in melting temperature (T_m) where X11P >X11C >X11 as determined by differential scanning fluorimetry. The X11P variant was tested for hydrolysis of beechwood xylan, which showed X6 as the major product followed by X3 and X4 XOs. The highest yield of 5.5 g total XOs product/mg enzyme was observed for X11P, equivalent to 3.7 fold higher than that of wild-type with XO production of >800 mg/g xylan. The X11P enzyme could be developed as a thermophilic biocatalyst for XO synthesis in biorefineries.

Fast saccharide mapping method for quality consistency evaluation of commercial xylooligosaccharides collected in China

Due to the extensive use of xylooligosaccharides (XOS) as functional food ingredients, many inferior goods and even adulterants are generally found in the market, which may pose a health hazard to certain populations. Chromatography method such as high-performance liquid chromatography (HPLC) and high-performance thin-layer chromatography (HPTLC) is traditionally applied for the quality analysis of XOS. However, it is time consuming due to the prolonged separation and pre- or post- derivatization procedure. In this study, a fast saccharide mapping method based on matrix-assisted laser desorption/time-of-flight mass spectrometry (MALDI-TOF-MS) was developed for the quality consistency analysis of 22 batches of XOS collected from different manufacturers in China. The time needed for saccharides analysis using MALDI-MS was less than 30 min for one plate, at least 6 times faster than that by the traditional HPTLC chromatography method. In addition, MALDI-MS possessed higher resolution for XOS with DP4-DP7 based on the difference of m/z, which is hardly separated using HPTLC. The results showed that XOS were present only in samples XY01-XY11, samples XY12-XY14 only consisted of hex oligosaccharides, and samples XY15-XY22 were free of oligosaccharides. These indicate that the quality consistency of XOS products in the China market was poor, which should be carefully investigated.

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Fast saccharide mapping method was developed based on MADLI-TOF-MS.

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Quality consistency of commercial xylooligosaccharides collected in China was evaluated.

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Glycosidic linkage analysis was also used for identification of xylooligosaccharides.

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Fifty percent of commercial xylooligosaccharides are mislabeled.

Insights Into the Role of Exposed Surface Charged Residues in the Alkali-Tolerance of GH11 Xylanase

Thermostable and alkaline- or acid-stable xylanases are more advantageous in agricultural and industrial fields. In this study, a rational structure-based design was conducted based on a thermostable GH11 xylanase TlXynA from Thermomyces lanuginosus to improved pH-tolerance. Four mutant enzymes (P1, P2, P3, and P4) and five variants (N1, N2, N3, N4, and N5) were constructed by substituting surface charged residue combinations using site-directed mutagenesis. Compared to the native enzyme, two mutants P1 and P2 showed higher acid tolerance, especially at pH 3.0, presented 50 and 40% of their maximum activity, respectively. In addition, four mutants N1, N2, N3 and N4 had higher tolerance than the native enzyme to alkaline environments (pH 7.0-9.0). At pH 9.0, the residual activities of N1, N2, N3, and N4 were 86, 78, 77, and 66%, respectively. In summary, an improved pH-tolerance design principle is being reported.

Increasing the nutritional value of strawberry puree by adding xylo-oligosaccharides

The present study identified the threshold concentration of xylo-oligosaccharides (XOS) that resulted in minimal quality changes (rheology, color, water activity, pH, and total soluble solids) in strawberry puree. Optimization of XOS concentration to 5% (w/w) did not significantly alter the quality attributes of the strawberry puree. In addition, this study also monitored the rheological properties, composition (total soluble solids, total phenolic content, flavonoids, and tannin content), physicochemical attributes (color, water activity, pH) and sensorial properties of XOS-enhanced (5%, w/w) strawberry puree after thermal processing (HTST: 75 °C, 15s and UHT: 121 °C, 2s) and storage after 1, 15, and 36 days at 4 °C and 55 °C. At 5% (w/w) concentration, the addition of XOS increased consumer preference without significantly compromising quality attributes. Thermally treated strawberry puree (HTST and UHT) were less preferred by consumers than fresh puree. However, all strawberry samples incorporated with XOS (5%, w/w) received statistically higher scores than the samples without the XOS addition. Thus, the proposed supplementation of strawberry puree with XOS could be a viable solution to increase consumers' dietary fiber intake with little need for behavioral changes.

Extremophile - An Adaptive Strategy for Extreme Conditions and Applications

The concurrence of microorganisms in niches that are hostile like extremes of temperature, pH, salt concentration and high pressure depends upon novel molecular mechanisms to enhance the stability of their proteins, nucleic acids, lipids and cell membranes. The structural, physiological and genomic features of extremophiles that make them capable of withstanding extremely selective environmental conditions are particularly fascinating. Highly stable enzymes exhibiting several industrial and biotechnological properties are being isolated and purified from these extremophiles. Successful gene cloning of the purified extremozymes in the mesophilic hosts has already been done. Various extremozymes such as amylase, lipase, xylanase, cellulase and protease from thermophiles, halothermophiles and psychrophiles are of industrial interests due to their enhanced stability at forbidding conditions. In this review, we made an attempt to point out the unique features of extremophiles, particularly thermophiles and psychrophiles, at the structural, genomic and proteomic levels, which allow for functionality at harsh conditions focusing on the temperature tolerance by them.

Halophiles and Their Vast Potential in Biofuel Production

Global warming and the limitations of using fossil fuels are a main concern of all societies, and thus, the development of alternative fuel sources is crucial to improving the current global energy situation. Biofuels are known as the best alternatives of unrenewable fuels and justify increasing extensive research to develop new and less expensive methods for their production. The most frequent biofuels are bioethanol, biobutanol, biodiesel, and biogas. The production of these biofuels is the result of microbial activity on organic substrates like sugars, starch, oil crops, non-food biomasses, and agricultural and animal wastes. Several industrial production processes are carried out in the presence of high concentrations of NaCl and therefore, researchers have focused on halophiles for biofuel production. In this review, we focus on the role of halophilic microorganisms and their current utilization in the production of all types of biofuels. Also, the outstanding potential of them and their hydrolytic enzymes in the hydrolysis of different kind of biomasses and the production of biofuels are discussed.

A novel approach to produce glucose from the supernatant obtained upon the dilute acid pre-treatment of rice straw and synergistic action of hydrolytic enzymes producing microbes

The present work refers to a process involving the use of dilute nitric acid pretreatment and enzymatic hydrolysis for the transformation of rice straw into simple sugars. Acid pre-treated rice straw was separated into the pulp and supernatant through centrifugation and filtration. The two fractions are then converted into simple sugars by combined action of microbes producing cellulase and laccase enzymes. These microbes were isolated from soil samples which were collected from different locations with varying altitudes, expected to harbour microbes with high-hydrolysing activity. The nitric acid pretreatment was carried out at 30 °C, 200 rpm for 72 h. After 72 h, the culture supernatants were analysed for the presence of glucose with the help of HPLC. The supernatant fraction separated after the acid pre-treated rice straw produced highest amount of glucose (205 mg/g of rice straw) upon subsequent hydrolysis with synergistic action of cellulase and laccase-producing microbes.

Xylan deterioration approach: Purification and catalytic behavior optimization of a novel β-1,4-d-xylanohydrolase from Geobacillus stearothermophilus KIBGE-IB29

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β-1,4-d-Xylanohydrolase from Geobacillus stearothermophilus KIBGE-IB29 was purified and characterized.

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The catalytic properties revealed significant stability over broad pH and temperature range.

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Native-PAGE and In-gel activity assay were carried out.

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Various organic solvents and detergents significantly improved the enzyme activity.

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β-1,4-d-Xylanohydrolase showed excellent storage stability for prospective industrial use.

The β-1,4-d-xylanohydrolase is an industry valuable catalytic protein and used to synthesize xylooligosaccharides and xylose. In the current study, β-1,4-d-xylanohydrolase from Geobacillus stearothermophilus KIBGE-IB29 was partially purified up to 9.5-fold with a recovery yield of 52%. It exhibited optimal catalytic activity at pH-7.0 and 50 °C within 5 min. Almost 50% activity retained at pH-4.0 to 9.0 however, 70% activity observed within the range of 40 °C to 70 °C. The β-1,4-d-xylanohydrolase showed a significant hydrolytic pattern with 48.7 kDa molecular mass. It was found that the enzymatic activity improved up to 160% with 1.0 mM ethanol. Moreover, the activity of enzyme drastically increased up to 2.3 and 1.5 fold when incubated with Tween 80 and Triton X-100 (1.0 mM), respectively. The β-1,4-d-xylanohydrolase also retained 72% activity at −80 °C after 180 days. Such a remarkable biochemical properties of β-1,4-d-xylanohydrolase make it possible to forecast its potential use in textile and food industries.

GH-10 and GH-11 Endo-1,4-β-xylanase enzymes from Kitasatospora sp. produce xylose and xylooligosaccharides from sugarcane bagasse with no xylose inhibition

A novel strategy for the low-cost, high-yield co-production of xylose and xylooligosaccharides together with no xylose inhibition was developed using a novel heterologous expression of XYN10Ks_480 endo-1,4-β-xylanase with a ricin-type β-trefoil type of domain and XYN11Ks_480 endo-1,4-β-xylanase with a CBM 2 superfamily from the Kitasatospora sp in an actinomycetes expression system. Xylose is the main building block for hemicellulose xylan. Our findings demonstrated high levels of expression and catalytic activity for XYN10Ks_480 during hydrolysis of the extracted xylan of bagasse, and three types of xylan-based substrates were used to produce xylose and xylooligosaccharides. However, hydrolysis by XYN11Ks_480 produced xylooligosaccharides without xylose formation. This study demonstrated how integrating sodium hypochlorite-extracted xylan and enzymatic hydrolysis could provide an alternative strategy for the generation of XOS from lignocellulosic material.

CRISPR-Cas9 Approach Constructing Cellulase sestc-Engineered Saccharomyces cerevisiae for the Production of Orange Peel Ethanol

The development of lignocellulosic bioethanol plays an important role in the substitution of petrochemical energy and high-value utilization of agricultural wastes. The safe and stable expression of cellulase gene sestc was achieved by applying the clustered regularly interspaced short palindromic repeats-Cas9 approach to the integration of sestc expression cassette containing Agaricus biporus glyceraldehyde-3-phosphate-dehydrogenase gene (gpd) promoter in the Saccharomyces cerevisiae chromosome. The target insertion site was found to be located in the S. cerevisiae hexokinase 2 by designing a gRNA expression vector. The recombinant SESTC protein exhibited a size of approximately 44 kDa in the engineered S. cerevisiae. By using orange peel as the fermentation substrate, the filter paper, endo-1,4-β-glucanase, exo-1,4-β-glucanase activities of the transformants were 1.06, 337.42, and 1.36 U/mL, which were 35.3-fold, 23.03-fold, and 17-fold higher than those from wild-type S. cerevisiae, respectively. After 6 h treatment, approximately 20 g/L glucose was obtained. Under anaerobic conditions the highest ethanol concentration reached 7.53 g/L after 48 h fermentation and was 37.7-fold higher than that of wild-type S. cerevisiae (0.2 g/L). The engineered strains may provide a valuable material for the development of lignocellulosic ethanol.

One-step process for producing prebiotic arabino-xylooligosaccharides from brewer's spent grain employing Trichoderma species

Xylooligosaccharides (XOS) are prebiotic nutraceuticals that can be sourced from lignocellulosic biomass, such as agro-residues. This study reports for the first time an optimization study of XOS production from agro-residues by direct fermentation using two Trichoderma species. A total of 13 residues were evaluated as potential substrates for single-step production. The best results were found for Trichoderma reesei using brewers' spent grain (BSG) as substrate. Under optimal conditions (3 days, pH 7.0, 30 °C and 20 g/L of BSG), a production yield of 38.3 ± 1.8 mg/g (xylose equivalents/g of BSG) was achieved. The obtained oligosaccharides were identified as arabino-xylooligosacharides (AXOS) with degree of polymerization from 2 to 5. One-step fermentation proved to be a promising strategy for AXOS production from BSG, presenting a performance comparable with the use of commercial enzymes. This study provides new insights towards the bioprocess integration, enabling further developments of low-cost bioprocesses for the production of these valuable compounds.

Technological advances and applications of hydrolytic enzymes for valorization of lignocellulosic biomass

Hydrolytic enzymes are indispensable tools in the production of various foodstuffs, drugs, and consumables owing to their applications in almost every industrial process nowadays. One of the foremost areas of interest involving the use of hydrolytic enzymes is in the transformation of lignocellulosic biomass into value added products. However, limitations of the processes due to inadequate enzyme activity and stability with a narrow range of pH and temperature optima often limit their effective usage. The innovative technologies, involving manipulation of enzyme activity and stability through mutagenesis, genetic engineering and metagenomics lead to a major leap in all the fields using hydrolytic enzymes. This article provides recent advancement towards the isolation and use of microbes for lignocellulosic biomass utilisation, microbes producing the hydrolytic enzymes, the modern age technologies used to manipulate and enhance the hydrolytic enzyme activity and the applications of such enzymes in value added products development from lignocellulosic biomass.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Purification, characterization and thermostability improvement of xylanase from Bacillus amyloliquefaciens and its application in pre-bleaching of kraft pulp

Xylanases have important industrial applications but are most extensively utilized in the pulp and paper industry as a pre-bleaching agent. We characterized a xylanase from Bacillus amyloliquefaciens strain SK-3 and studied it for kraft pulp bleaching. The purified enzyme had a molecular weight of ~50 kDa with optimal activity at pH 9.0 and 50 °C. The enzyme showed good activity retention (85%) after 2 h incubation at 50 °C and pH 9.0. This enzyme obeyed Michaelis–Menten kinetics with regard to beechwood xylan with K_m and V_max values of 5.6 mg/ml, 433 μM/min/mg proteins, respectively. The enzyme activity was stimulated by Mn²⁺, Ca²⁺ and Fe²⁺ metal ions. Further, it also showed good tolerance to phenolics (2 mM) in the presence of syringic acid (no loss), cinnamic acid (97%), benzoic acid (94%) and phenol (97%) activity retention. The thermostability of xylanase was increased by 6.5-fold in presence of sorbitol (0.75 M). Further, pulp treated with 20U/g of xylanase (20IU/g) alone and with sorbitol (0.75M) reduced kappa number by 18.3 and 23.8%, respectively after 3 h reaction. In summary, presence of xylanase shows good pulp-bleaching activity, good tolerance to phenolics, lignin and metal ions and is amenable to thermostability improvement by addition of polyols. The SEM image showed significant changes on the surface of xylanase-treated pulp fiber as a result of xylan hydrolysis.

Bifunctional recombinant cellulase-xylanase (rBhcell-xyl) from the polyextremophilic bacterium Bacillus halodurans TSLV1 and its utility in valorization of renewable agro-residues

The thermostable bifunctional CMCase and xylanase encoding gene (rBhcell-xyl) from Bacillus halodurans TSLV1 has been expressed in Escherichia coli. The recombinant E. coli produced rBhcell-xyl (CMCase 2272 and 910 U L^-1 xylanase). The rBhcell-xyl is a ~62-kDa monomeric protein with temperature and pH optima of 60 °C and 6.0 with T_1/2 of 7.0 and 3.5 h at 80 °C for CMCase and xylanase, respectively. The apparent K _m values (CMC and Birchwood xylan) are 3.8 and 3.2 mg mL^-1. The catalytic efficiency (k _cat/K _m ) values of xylanase and CMCase are 657 and 171 mL mg^-1 min^-1, respectively. End-product analysis confirmed that rBhcell-xyl is a unique endo-acting enzyme with exoglucanase activity. The rBhcell-xyl is a GH5 family enzyme possessing single catalytic module and carbohydrate binding module. The action of rBhcell-xyl on corn cobs and wheat bran liberated reducing sugars, which can be fermented to bioethanol and fine biochemicals.

Suitability of the alkalistable carbonic anhydrase from a polyextremophilic bacterium Aeribacillus pallidus TSHB1 in biomimetic carbon sequestration

Carbonic anhydrase (CA) was produced from the polyextremophilic (halotolerant, moderately thermophilic and alkaliphilic) bacterium Aeribacillus pallidus TSHB1 isolated from water and sediment samples of Choti Anhoni hot spring of Pipariya, Madhya Pradesh (India), is being reported to be suitable for carbon sequestration. Growth and CA production were inhibited at higher CO2 concentration (5-10 %). Under optimized culture variables (tryptone 0.8 %, yeast extract 0.08 %, glucose 1 %, micronutrient solution 1 %, inoculums size 1.10 %, agitation 200 at pH 8, and temperature 55 °C), 3.7-fold higher CA production was attained than that under unoptimized conditions. The zymogram analysis of the partially purified CA revealed an activity band corresponding to 32 kDa. The enzyme is stable in the pH range between 8.0 and 11.0 with T 1/2 of 40, 15, and 8 min at 60, 70, and 80 °C, respectively. The CA of A. pallidus displayed a marked enhancement in the rate of CaCO3 precipitation from aqueous CO2. The CA-aided formation of CaCO3 was 42.5 mg mg(-1) protein. Scanning electron microscopy revealed the formation of rhomboid calcite crystals. This is the first report on the production and applicability of CA from the polyextremophilic A. pallidus in carbon sequestration.

Generation of xylooligosaccharides from microwave irradiated agroresidues using recombinant thermo-alkali-stable endoxylanase of the polyextremophilic bacterium Bacillus halodurans expressed in Pichia pastoris

The recombinant Pichia pastoris harboring the endoxylanase gene (TSEV1xyl) of Bacillus halodurans TSEV1 yielded a high titer of extracellular xylanase (502±23 U ml(-1)) on induction with methanol. The purified recombinant xylanase (TSEV1xyl) displayed optimal activity at 80°C and pH 9.0. The glycosylated recombinant xylanase exhibited higher thermostability (T1/2 of 45 min at 80°C) than the native enzyme (T1/2 of 35 min at 80°C). The agroresidues subjected to pretreatment (soaking in alkali followed by microwave irradiation) liberated xylooligosaccharides (XOS) upon hydrolysis with the recombinant xylanase. The removal of unhydrolyzed agroresidues, xylanase and xylose from the hydrolysate by two-step ultrafiltration led to the purification of XOS as confirmed by TLC as well as HPLC analysis.

Applicability of recombinant β-xylosidase from the extremely thermophilic bacterium Geobacillus thermodenitrificans in synthesizing alkylxylosides

The β-xylosidase encoding gene (XsidB) of the extremely thermophilic bacterium Geobacillus thermodenitrificans has been cloned and expressed in Escherichia coli. The homotrimeric recombinant XsidB is of 204.0kDa, which is optimally active at 60°C and pH 7.0 with T1/2 of 58min at 70°C. The β-xylosidase remains unaffected in the presence of most metal ions and organic solvents. The Km [p-nitrophenyl β-xyloside (pNPX)], Vmax and kcat values of the enzyme are 2×10(-3)M, 1250μmolesmg(-1)min(-1) and 13.20×10(5)min(-1), respectively. The enzyme catalyzes transxylosylation reactions in the presence of alcohols as acceptors. The pharmaceutically important β-methyl-d-xylosides could be produced using pNPX as the donor and methanol as acceptor. The products of transxylosylation were identified by TLC and HPLC, and the structure was confirmed by (1)H NMR analysis. The enzyme is also useful in synthesizing transxylosylation products from the wheat bran hydrolysate.

Expression and characterization of hyperthermotolerant xylanases, SyXyn11P and SyXyn11E, in Pichia pastoris and Escherichia coli

Both Syxyn11P and Syxyn11E, two codon-optimized genes encoding glycoside hydrolase (GH) family 11 hyperthermotolerant xylanases (designated SyXyn11P and SyXyn11E), were synthesized and inserted into pPIC9K(M) and pET-28a(+) vectors, respectively. The resulting recombinant expression vectors, pPIC9K(M)-Syxyn11P and pET-28a(+)-Syxyn11E, were transformed into Pichia pastoris GS115 and Escherichia coli BL21, respectively. The maximum activities of two recombinant xylanases (reSyXyn11P and reSyXyn11E) expressed in P. pastoris and E. coli reached 30.9 and 17.8 U/ml, respectively. The purified reSyXyn11P and reSyXyn11E displayed the same pH optimum at 6.5 and pH stability at a broad range of 4.5-9.0. The temperature optimum and stability of reSyXyn11P were 85 and 80 °C, higher than those of reSyXyn11E, respectively. Their activities were not significantly affected by metal ions tested and EDTA, but strongly inhibited by Mn(2+) and Ag(+). The K m and V max of reSyXyn11P toward birchwood xylan were 4.3 mg/ml and 694.6 U/mg, whose K m was close to that (4.8 mg/ml), but whose V max was much higher than that (205.6 U/mg) of reSyXyn11E. High-performance liquid chromatography analysis indicated that xylobiose and xylotriose as the major products were excised from insoluble corncob xylan by reSyXyn11P.

Xylanase production from Bacillus aerophilus KGJ2 and its application in xylooligosaccharides preparation

Xylanolytic enzyme was produced using a newly isolated Bacillus aerophilus KGJ2 and low cost lignocellulosic sources in solid state fermentation. Seven different agricultural residues (wheat bran, tea dust, saw dust, paper waste, cassava bagasse, rice straw and rice husk) and six nitrogen source namely yeast extract, beef extract, peptone, ammonium nitrate, ammonium sulphate, and ammonium chloride were examined for xylanase production. Upon initial screening, wheat bran and ammonium chloride were chosen as suitable carbon source and nitrogen source respectively. Plackett-Burman fractional factorial design was employed to screen the important process variables affecting enzyme production. Substrate concentration, nitrogen source, moisture content and MgSO4·7H2O were identified as statistically significant variables. Subsequently Box-Behnken method was used to optimize the process conditions to achieve maximum xylanase yield. Under optimized conditions xylanase yield was 45.9 U/gds. Best xylanase activity was obtained at 70 °C and pH 4.0. It retained more than 90% activity after incubation at 80-90 °C for 60 min. The hydrolytic efficiency of xylanase on xylan was examined and xylobiose, xylotriose and xylotetrose were obtained as hydrolytic products.

Genomic and enzymatic results show Bacillus cellulosilyticus uses a novel set of LPXTA carbohydrases to hydrolyze polysaccharides

Background

Alkaliphilic Bacillus species are intrinsically interesting due to the bioenergetic problems posed by growth at high pH and high salt. Three alkaline cellulases have been cloned, sequenced and expressed from Bacillus cellulosilyticus N-4 (Bcell) making it an excellent target for genomic sequencing and mining of biomass-degrading enzymes.

Methodology/Principal Findings

The genome of Bcell is a single chromosome of 4.7 Mb with no plasmids present and three large phage insertions. The most unusual feature of the genome is the presence of 23 LPXTA membrane anchor proteins; 17 of these are annotated as involved in polysaccharide degradation. These two values are significantly higher than seen in any other Bacillus species. This high number of membrane anchor proteins is seen only in pathogenic Gram-positive organisms such as Listeria monocytogenes or Staphylococcus aureus. Bcell also possesses four sortase D subfamily 4 enzymes that incorporate LPXTA-bearing proteins into the cell wall; three of these are closely related to each other and unique to Bcell. Cell fractionation and enzymatic assay of Bcell cultures show that the majority of polysaccharide degradation is associated with the cell wall LPXTA-enzymes, an unusual feature in Gram-positive aerobes. Genomic analysis and growth studies both strongly argue against Bcell being a truly cellulolytic organism, in spite of its name. Preliminary results suggest that fungal mycelia may be the natural substrate for this organism.

Conclusions/Significance

Bacillus cellulosilyticus N-4, in spite of its name, does not possess any of the genes necessary for crystalline cellulose degradation, demonstrating the risk of classifying microorganisms without the benefit of genomic analysis. Bcell is the first Gram-positive aerobic organism shown to use predominantly cell-bound, non-cellulosomal enzymes for polysaccharide degradation. The LPXTA-sortase system utilized by Bcell may have applications both in anchoring cellulases and other biomass-degrading enzymes to Bcell itself and in anchoring proteins other Gram-positive organisms.