Purification and characterization of a cellulase-free, thermostable xylanase from Streptomyces rameus L2001 and its biobleaching effect on wheat straw pulp

Cold-active microbial enzymes and their biotechnological applications

Microorganisms known as psychrophiles/psychrotrophs, which survive in cold climates, constitute majority of the biosphere on Earth. Their capability to produce cold-active enzymes along with other distinguishing characteristics allows them to survive in the cold environments. Due to the relative ease of large-scale production compared to enzymes from plants and animals, commercial uses of microbial enzyme are alluring. The ocean depths, polar, and alpine regions, which make up over 85% of the planet, are inhabited to cold ecosystems. Microbes living in these regions are important for their metabolic contribution to the ecosphere as well as for their enzymes, which may have potential industrial applications. Cold-adapted microorganisms are a possible source of cold-active enzymes that have high catalytic efficacy at low and moderate temperatures at which homologous mesophilic enzymes are not active. Cold-active enzymes can be used in a variety of biotechnological processes, including food processing, additives in the detergent and food industries, textile industry, waste-water treatment, biopulping, environmental bioremediation in cold climates, biotransformation, and molecular biology applications with great potential for energy savings. Genetically manipulated strains that are suitable for producing a particular cold-active enzyme would be crucial in a variety of industrial and biotechnological applications. The potential advantage of cold-adapted enzymes will probably lead to a greater annual market than for thermo-stable enzymes in the near future. This review includes latest updates on various microbial source of cold-active enzymes and their biotechnological applications.

Soil microbial community development across a 32-year coastal wetland restoration time series and the relative importance of environmental factors

Soil microbes play key roles in ecosystem functioning through processes such as organic matter decomposition, nutrient and carbon cycling, and regulating vegetation structure and productivity. Coastal marshes are situated at the confluence of terrestrial and marine ecosystems; thus, their soils support abundant and diverse microbiota which facilitate globally important biogeochemical processes including nutrient cycling and greenhouse gas fluxes. With coastal marsh ecosystems threatened by relative sea level rise, subsidence, and development, mitigation for the loss of marshes is becoming commonplace. Despite the widespread implementation of marsh construction projects, little is known about the development and variability of microbial communities in created marshes. For this study, we tested the hypothesis that microbial community composition differs across created marshes of different ages and between created and natural marshes. We also hypothesized that the microbial community would be correlated with soil properties including soil organic carbon and nitrogen content, which were predicted to increase with marsh age. To test these hypotheses, we determined dominant microbial groups and environmental characteristics from six constructed marshes ranging in age from 0 to 32 years old, as well as an adjacent natural marsh. Our results revealed that microbial biomass estimates increased with marsh age except for the high elevation 20-year old marsh, yet each marsh contained a distinct microbial community composition. Across marshes, microbial community composition was significantly related to soil C:N ratio with an increase in total microbial abundance and actinomycetes and GM+ bacteria with an increase in soil C to N ratio. Additionally, shifts in dominant microbial groups were associated with differences in vegetation, elevation, and marsh age. The natural marsh community grouped more closely with younger rather than older marshes suggesting age is less important than environmental conditions. This study shows that microbial communities are not homogenized across restoration sites and do not necessarily converge to be similar to natural marshes over time. Local biotic and environmental conditions were correlated with microbial compositions, yet in seemingly similar conditions, microbial groups also differed. The effect of differences in microbial compositions on ecological functions are yet to be fully understood.

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.

Genetically Modified Sugarcane Intercropping Soybean Impact on Rhizosphere Bacterial Communities and Co-occurrence Patterns

Strategies involving genes in the dehydration-responsive element binding (DREB) family, which participates in drought stress regulation, and intercropping with legumes are becoming prominent options in promoting sustainable sugarcane cultivation. An increasing number of studies focusing on root interactions in intercropping systems, particularly involving transgenic crops, are being conducted to better understand and thus, harness beneficial soil microbes to enhance plant growth. We designed experiments to investigate the characteristics of two intercropping patterns, soybean with wild-type (WT) sugarcane and soybean with genetically modified (GM) Ea-DREB2B-overexpressing sugarcane, to assess the response of the rhizosphere microbiota to the different cropping patterns. Bacterial diversity in the rhizosphere microbial community differed between the two intercropping pattens. In addition, the biomass of GM sugarcane that intercropped with soybean was significantly improved compared with WT sugarcane, and the aboveground biomass and root biomass of GM soybean intercropping sugarcane increased by 49.15 and 46.03% compared with monoculture. Furthermore, a beneficial rhizosphere environment for the growth of Actinobacteria was established in the systems intercropped with GM sugarcane. Improving the production mode of crops by genetic modification is a key strategy to improving crop yields and provides new opportunities to further investigate the effects of intercropping on plant roots and soil microbiota. Thus, this study provides a basis for selecting suitable sugarcane-soybean intercropping patterns and a theoretical foundation for a sustainable sugarcane production.

Characterization of glycoside hydrolase family 11 xylanase from Streptomyces sp. strain J103; its synergetic effect with acetyl xylan esterase and enhancement of enzymatic hydrolysis of lignocellulosic biomass

Background

Xylanase-containing enzyme cocktails are used on an industrial scale to convert xylan into value-added products, as they hydrolyse the β-1,4-glycosidic linkages between xylopyranosyl residues. In the present study, we focused on xynS1, the glycoside hydrolase (GH) 11 xylanase gene derived from the Streptomyces sp. strain J103, which can mediate XynS1 protein synthesis and lignocellulosic material hydrolysis.

Results

xynS1 has an open reading frame with 693 base pairs that encodes a protein with 230 amino acids. The predicted molecular weight and isoelectric point of the protein were 24.47 kDa and 7.92, respectively. The gene was cloned into the pET-11a expression vector and expressed in Escherichia coli BL21(DE3). Recombinant XynS1 (rXynS1) was purified via His-tag affinity column chromatography. rXynS1 exhibited optimal activity at a pH of 5.0 and temperature of 55 °C. Thermal stability was in the temperature range of 50–55 °C. The estimated K_m and V_max values were 51.4 mg/mL and 898.2 U/mg, respectively. One millimolar of Mn²⁺ and Na⁺ ions stimulated the activity of rXynS1 by up to 209% and 122.4%, respectively, and 1 mM Co²⁺ and Ni²⁺ acted as inhibitors of the enzyme. The mixture of rXynS1, originates from Streptomyces sp. strain J103 and acetyl xylan esterase (AXE), originating from the marine bacterium Ochrovirga pacifica, enhanced the xylan degradation by 2.27-fold, compared to the activity of rXynS1 alone when Mn²⁺ was used in the reaction mixture; this reflected the ability of both enzymes to hydrolyse the xylan structure. The use of an enzyme cocktail of rXynS1, AXE, and commercial cellulase (Celluclast® 1.5 L) for the hydrolysis of lignocellulosic biomass was more effective than that of commercial cellulase alone, thereby increasing the relative activity 2.3 fold.

Conclusion

The supplementation of rXynS1 with AXE enhanced the xylan degradation process via the de-esterification of acetyl groups in the xylan structure. Synergetic action of rXynS1 with commercial cellulase improved the hydrolysis of pre-treated lignocellulosic biomass; thus, rXynS1 could potentially be used in several industrial applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01619-x.

Conversion of Wheat Bran to Xylanases and Dye Adsorbent by Streptomyces thermocarboxydus

Agro-byproducts can be utilized as effective and low-cost nutrient sources for microbial fermentation to produce a variety of usable products. In this study, wheat bran powder (WBP) was found to be the most effective carbon source for xylanase production by Streptomyces thermocarboxydus TKU045. The optimal media for xylanase production was 2% (w/v) WBP, 1.50% (w/v) KNO₃, 0.05% (w/v) MgSO₄, and 0.10% (w/v) K₂HPO₄, and the optimal culture conditions were 50 mL (in a 250 mL-volume Erlenmeyer flask), initial pH 9.0, 37 °C, 125 rpm, and 48 h. Accordingly, the highest xylanase activity was 6.393 ± 0.130 U/mL, 6.9-fold higher than that from un-optimized conditions. S. thermocarboxydus TKU045 secreted at least four xylanases with the molecular weights of >180, 36, 29, and 27 kDa when cultured on the WBP-containing medium. The enzyme cocktail produced by S. thermocarboxydus TKU045 was optimally active over a broad range of temperature and pH (40–70 °C and pH 5–8, respectively) and could hydrolyze birchwood xylan to produce xylobiose as the major product. The obtained xylose oligosaccharide (XOS) were investigated for 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and the growth effect of lactic acid bacteria. Finally, the solid waste from the WBP fermentation using S. thermocarboxydus TKU045 revealed the high adsorption of Congo red, Red 7, and Methyl blue. Thus, S. thermocarboxydus TKU045 could be a potential strain to utilize wheat bran to produce xylanases for XOS preparation and dye adsorbent.

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.

Aspergillus sydowii: Genome Analysis and Characterization of Two Heterologous Expressed, Non-redundant Xylanases

A prerequisite for the transition toward a biobased economy is the identification and development of efficient enzymes for the usage of renewable resources as raw material. Therefore, different xylanolytic enzymes are important for efficient enzymatic hydrolysis of xylan-heteropolymers. A powerful tool to overcome the limited enzymatic toolbox lies in exhausting the potential of unexplored habitats. By screening a Vietnamese fungal culture collection of 295 undiscovered fungal isolates, 12 highly active xylan degraders were identified. One of the best xylanase producing strains proved to be an Aspergillus sydowii strain from shrimp shell (Fsh102), showing a specific activity of 0.6 U/mg. Illumina dye sequencing was used to identify our Fsh102 strain and determine differences to the A. sydowii CBS 593.65 reference strain. With activity based in-gel zymography and subsequent mass spectrometric identification, three potential proteins responsible for xylan degradation were identified. Two of these proteins were cloned from the cDNA and, furthermore, expressed heterologously in Escherichia coli and characterized. Both xylanases, were entirely different from each other, including glycoside hydrolases (GH) families, folds, substrate specificity, and inhibition patterns. The specific enzyme activity applying 0.1% birch xylan of both purified enzymes were determined with 181.1 ± 37.8 or 121.5 ± 10.9 U/mg for xylanase I and xylanase II, respectively. Xylanase I belongs to the GH11 family, while xylanase II is member of the GH10 family. Both enzymes showed typical endo-xylanase activity, the main products of xylanase I are xylobiose, xylotriose, and xylohexose, while xylobiose, xylotriose, and xylopentose are formed by xylanase II. Additionally, xylanase II showed remarkable activity toward xylotriose. Xylanase I is stable when stored up to 30°C and pH value of 9, while xylanase II started to lose significant activity stored at pH 9 after exceeding 3 days of storage. Xylanase II displayed about 40% activity when stored at 50°C for 24 h. The enzymes are tolerant toward mesophilic temperatures, while acting in a broad pH range. With site directed mutagenesis, the active site residues in both enzymes were confirmed. The presented activity and stability justify the classification of both xylanases as highly interesting for further development.

High-yield grass Pennisetum sinese Roxb plantation and organic manure alter bacterial and fungal communities structure in an ecological agriculture farm

Pennisetum sinese Roxb (P. sinese) is an efficient and economic energy crop for its high productivity, and has been well studied in its application in phytoremediation and fodder production. However, little is known about how P. sinese plantation and fermented manures of P. sinese-feed livestock affect the composition of soil bacterial and fungal communities. In this study, 16S rRNA/ITS1 gene-based Illumina Miseq sequencing was employed to compare the bacterial and fungal community structure among soils that had been subjected to uncultivated control (CK), 2-year P. sinese plantation (P), and P. sinese plantation combined with the use of organic manures (P-OM) in a "P. sinese-breeding industry" ecological agriculture farm. The results found microbial communities were altered by P. sinese plantation and fertilization. The P. sinese plantation resulted in increased Actinobacteria and Planctomycetes abundance. Comparatively, significant increased abundance of Chloroflexi, Firmicutes, Nitrospirae, and Euryarchaeota, and genes related with nitrogen and carbon metabolic pathways based on PICRUSt prediction was observed in P-OM soil. Fungal compositions suggested a markedly increased abundance of Ascomycota in P soil. Potential organic matter decomposers Candida, Thermoascus, and Aspergillus were enriched in P soil, indicating the enhanced role of fungi in litter decomposition. Redundancy analysis suggested that soil properties (NH₄⁺-N, total nitrogen, organic matter content, and soil water content) significantly correlated with the changes of microbial compositions (P < 0.05). These results highlight the divergence of microbial communities occurs during P. sinese-based plantation, implying functional diversification of soil ecosystem in P. sinese fields.

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.

Mutagenesis of N-terminal residues confer thermostability on a Penicillium janthinellum MA21601 xylanase

BACKGROUND

A mesophilic xylanase PjxA from Penicillium janthinellum MA21601 has high specific activity under acidic condition and holds great potential for applications in the animal feed industry. To enhance the thermostability of xylanase PjxA, two mutation strategies in the N-terminal region were examined and then integrated into the xylanase to further improvement. The recombinant xylanase PTxA-DB (The meaning of DB is disulfide-bridge.) was constructed by replacement of five residues in the mutated region in TfxA (T10Y, N11H, N12D, Y15F, N30 L), combined with an additional disulfide bridge in the N-terminal region.

RESULTS

The T_m value of mutant PTxA-DB was improved from 21.3 °C to 76.6 °C, and its half-life was found to be 53.6 min at 60 °C, 107-fold higher than the wild type strain. The location of the disulfide bridge (T2C-T29C) was between the irregular loop and the β-strand A2, accounting for most of the improvement in thermostability of PjxA. Further analysis indicated T2C, T29C, N30 L and Y15F lead to increase N-terminal hydrophobicity. Moreover, the specific activity and substrate affinity of PTxA-DB were also enhanced under the acidic pH values.

CONCLUSIONS

These results indicated PTxA-DB could be a prospective additive to industrial animal feeds.

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.

Taxonomic identification of the thermotolerant and fast-growing fungus Lichtheimia ramosa H71D and biochemical characterization of the thermophilic xylanase LrXynA

The zygomycete fungus Lichtheimia ramosa H71D, isolated from sugarcane bagasse compost, was identified by applying phylogenetic analysis based on the DNA sequence of the Internal Transcribed Spacer (ITS), and subsequent secondary structure analysis of ITS2. L. ramosa H71D was able to grow over a wide range of temperatures (25–45 °C), manifesting optimal growth at 37 °C. A 64 kDa xylanase (named LrXynA) was purified from the culture supernatant of L. ramosa H71D grown on 2% carboxymethylcellulose (CMC), as the only carbon source. LrXynA displayed optimal activity at pH 6 and temperature of 65 °C. The enzyme retained more than 50% of its maximal activity over a broad range of pH values (4.5–7.5). Enzyme half-life (t_½) times at 55, 65 and 75 °C were 80, 25, and 8 min, respectively. LrXynA showed higher affinity (k_M of 2.87 mg/mL) and catalytic efficiency (k_cat/k_M of 0.651 mg s/mL) towards Beechwood xylan in comparison to other substrates such as Birchwood xylan, Oat-spelt xylan, CMC, Avicel and Solka floc. The predominant final products from LrXynA-mediated hydrolysis of Beechwood xylan were xylobiose and xylotriose, suggesting that the enzyme is an endo-β-1,4 xylanase. Scanning electron microscopy (SEM) imaging of sugar cane bagasse (SCB) treated with LrXynA, alone or in combination with commercial cellulases, showed a positive effect on the hydrolysis of SCB. To our knowledge, this is the first report focusing on the biochemical and functional characterization of an endo-β-1,4 xylanase from the thermotolerant and fast-growing fungus Lichtheimia ramosa.

Gene Expression and Molecular Characterization of a Xylanase from Chicken Cecum Metagenome

A xylanase gene xynA_MG1 with a 1,116-bp open reading frame, encoding an endo-β-1,4-xylanase, was cloned from a chicken cecum metagenome. The translated XynA_MG1 protein consisted of 372 amino acids including a putative signal peptide of 23 amino acids. The calculated molecular mass of the mature XynA_MG1 was 40,013 Da, with a theoretical pI value of 5.76. The amino acid sequence of XynA_MG1 showed 59% identity to endo-β-1,4-xylanase from Prevotella bryantii and Prevotella ruminicola and 58% identity to that from Prevotella copri. XynA_MG1 has two conserved motifs, DVVNE and TEXD, containing two active site glutamates and an invariant asparagine, characteristic of GH10 family xylanase. The xynA_MG1 gene without signal peptide sequence was cloned and fused with thioredoxin protein (Trx.Tag) in pET-32a plasmid and overexpressed in Escherichia coli Tuner™(DE3)pLysS. The purified mature XynA_MG1 was highly salt-tolerant and stable and displayed higher than 96% of its catalytic activity in the reaction containing 1 to 4 M NaCl. It was only slightly affected by common organic solvents added in aqueous solution to up to 5 M. This chicken cecum metagenome-derived xylanase has potential applications in animal feed additives and industrial enzymatic processes requiring exposure to high concentrations of salt and organic solvents.

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.

Engineering a xylanase from Streptomyce rochei L10904 by mutation to improve its catalytic characteristics

Protein engineering was performed by N-terminal region replacement and site-directed mutagenesis in the cord of a xylanase (Srxyn) from Streptomyce rochei L10904 to improve its catalytic characteristics. Three mutants SrxynF, SrxynM and SrxynFM displayed 2.1-fold, 3.2-fold and 5.3-fold higher specific activities than that of Srxyn, respectively. Moreover, all of the mutants showed greater substrate affinity and k_cat/K_m than the native Srxyn. In addition, the enzymes showed improved hydrolysis characteristics, of which the most noteworthy is the enhanced ability of producing xylobiose (X2) and xylotriose (X3) from polymeric substrates. The engineered xylanases have greater potential for applications in oligosaccharide preparation industry.

Improvement for enhanced xylanase production by Cellulosimicrobium cellulans CKMX1 using central composite design of response surface methodology

The effects of yeast extract (X₁), NH₄NO₃ (X₂), peptone (X₃), urea (X₄), CMC (X₅), Tween 20 (X₆), MgSO₄ (X₇), and CaCO₃ (X₈) on production of xylanase from Cellulosimicrobium cellulans CKMX1 were optimized by statistical analysis using response surface methodology (RSM). The RSM was used to optimize xylanase production by implementing the Central composite design. Statistical analysis of the results showed that the linear, interaction and quadric terms of these variables had significant effects. However, only the linear effect of X₄, X₅, interaction effect of X₁X₇, X₁X₈, X₂X₃, X₂X₈, X₃X₆, X₃X₈, X₄X₆, X₄X₇, X₅X₇, X₅X₈ and quadratic effect of X ₃² , X ₅² and X ₇² found to be insignificant terms in the quadratic model and had no response at significant level. The minimum and maximum xylanase production obtained was 331.50 U/g DBP and 1027.65 U/g DBP, respectively. The highest xylanase activity was obtained from Run No. 30, which consisted of yeast extract (X₁), 1.00 g (%); NH₄NO₃ (X₂), 0.20 g (%); peptone (X₃), 1.00 g (%); urea (X₄), 10 mg (%); CMC (X₅), 1.00 g (%); Tween 20 (X₆), 0.02 mL (%); CaCO₃ (X₇), 0.50 g (%) and MgSO₄ (X₈), 9.0 g (%). The optimization resulted in 3.1-fold increase of xylanase production, compared with the lowest xylanase production of 331.50 U/g DBP after 72 h of incubation in stationary flask experiment. Application of cellulase-free xylanase in pulp biobleaching from C. cellulans CKMX1 under C-E_P-D sequence has been shown to bring about a 12.5 % reduction of chlorine, decrease of 0.8 kappa points (40 %), and gain in brightness was 1.42 % ISO points in 0.5 % enzyme treated pulp as compared to control.

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

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

Insight into glycoside hydrolases for debranched xylan degradation from extremely thermophilic bacterium Caldicellulosiruptor lactoaceticus

Caldicellulosiruptor lactoaceticus 6A, an anaerobic and extremely thermophilic bacterium, uses natural xylan as carbon source. The encoded genes of C. lactoaceticus 6A for glycoside hydrolase (GH) provide a platform for xylan degradation. The GH family 10 xylanase (Xyn10A) and GH67 α-glucuronidase (Agu67A) from C. lactoaceticus 6A were heterologously expressed, purified and characterized. Both Xyn10A and Agu67A are predicted as intracellular enzymes as no signal peptides identified. Xyn10A and Agu67A had molecular weight of 47.0 kDa and 80.0 kDa respectively as determined by SDS-PAGE, while both appeared as homodimer when analyzed by gel filtration. Xyn10A displayed the highest activity at 80 °C and pH 6.5, as 75 °C and pH 6.5 for Agu67A. Xyn10A had good stability at 75 °C, 80 °C, and pH 4.5-8.5, respectively, and was sensitive to various metal ions and reagents. Xyn10A possessed hydrolytic activity towards xylo-oligosaccharides (XOs) and beechwood xylan. At optimum conditions, the specific activity of Xyn10A was 44.6 IU/mg with beechwood xylan as substrate, and liberated branched XOs, xylobiose, and xylose. Agu67A was active on branched XOs with methyl-glucuronic acids (MeGlcA) sub-chains, and primarily generated XOs equivalents and MeGlcA. The specific activity of Agu67A was 1.3 IU/mg with aldobiouronic acid as substrate. The synergistic action of Xyn10A and Agu67A was observed with MeGlcA branched XOs and xylan as substrates, both backbone and branched chain of substrates were degraded, and liberated xylose, xylobiose, and MeGlcA. The synergism of Xyn10A and Agu67A provided not only a thermophilic method for natural xylan degradation, but also insight into the mechanisms for xylan utilization of C. lactoaceticus.

Purification and characterization of cellulase-free low molecular weight endo β-1,4 xylanase from an alkalophilic Cellulosimicrobium cellulans CKMX1 isolated from mushroom compost

Alkalophilic Cellulosimicrobium cellulans CKMX1 isolated from mushroom compost is first report on actinomycetes that has the ability to produce thermostable cellulase-free xylanase, which is an important industrial enzyme used in the pulp and paper industry. Strain CKMX1 was characterized by metabolic fingerprinting, whole-cell fatty acids methyl ester analysis and 16Sr DNA and found to be C. cellulans CKMX1.The enzyme was purified by gel permeation and anion exchange chromatography and had a molecular mass of 29 kDa. Xylanase activity was optimum at pH 8.0 and 55 °C. The enzyme was somewhat thermostable, retaining 50 % of the original activity after incubation at 50 °C for 30 min. The xylanase had K m and V max values of 2.64 mg/ml and 2,000 µmol/min/mg protein in oat spelt xylan, respectively. All metal ions except HgCl2, CoCl2 as well as CdCl2 were well tolerated and did not adversely affect xylanase activity. The deduced internal amino acid sequence of C. cellulans CKMX1 xylanase by matrix assisted laser desorption ionization-time of flight mass spectrometry resembled the sequence of β-1,4-endoxylanase, which is a member of glycoside hydrolase family 11. Some of the novel characteristics that make this enzyme potentially effective in xylan biodegradation could be useful for pulp and paper biobleaching are discussed in this manuscript.

Characterization of cattle fecal Streptomyces strains converting cellulose and hemicelluloses into reducing sugars

To characterize Streptomyces isolated from cattle feces for converting lignocellulose into reducing sugars, five Streptomyces strains were screened. All the strains could convert lignocellulose into reducing sugars. The strain A16 accumulate 3.3-folds more reducing sugars on cottonseed shells treated with ethanol than without the treatment (P < 0.05). The five strains did not accumulate more reducing sugars on rice straws and wheat brans than those on cottonseed shells. Compared with A10 alone, the microbial combination of F1 + A10 accumulated 19, 61, and 25 % less reducing sugars on cottonseed shell, rice straw, and wheat bran than those by A10 solely, respectively (P < 0.05). Further studies indicated that the activities of avicelase and xylanase were not correlated with the reducing sugar amount accumulated by the test strains. Strain A7 could produce more cellular lipids with xylose and glucose as the sole carbon sources. This study shows the potential for Streptomyces strains from herbivore feces to convert lignocelluloses into lipids and reducing sugars for fuel production.

Molecular identification using ITS sequences and genome shuffling to improve 2-deoxyglucose tolerance and xylanase activity of marine-derived fungus, Aspergillus sp. NRCF5

During the screening of xylanolytic enzyme from marine-derived fungi isolated from the inner tissue of Egyptian soft coral Rhytisma sp., one strain, NRCF5, exhibited high enzyme activity with 0.1 % (w/v) antimetabolite 2-deoxyglucose (2DG) tolerance. This fungal strain was identified as Aspergillus sp. NRCF5 based on its morphological characteristics and internal transcribed spacer (ITS) sequences. The ITS region of hyperactive xylanolytic strain (NRCF5) was amplified, sequenced, and submitted to GenBank (accession no. JQ277356). To apply the fundamental principles of genome shuffling in breeding of xylanase-producing fungi, marine-derived fungus Aspergillus sp. NRCF5 was used as starting strain in this work and applied for induction of genetic variability using different combinations and doses of mutagens. Five mutants with high xylanase activity and 0.25 % (w/v) antimetabolite 2DG tolerance were obtained from the populations generated by the mutation of combination between ultraviolet irradiation (UV, 5 min) and N-methyl-N-nitro-N-nitrosoguanidine (NTG, 100 μg/ml) for 30 (UNA) and 60 (UNB)min as well as NTG (100 μg/ml) and ethidium bromide (250 μg/ml) for 30 (NEA) and 60 (NEB)min. Then, they were subjected for recursive protoplast fusion. Seven hereditarily stable recombinants with high xylanase activity and 1.0 % (w/v) 2DG tolerance were obtained by four rounds of genome shuffling. Among them, a high xylanase-producing recombinant, R4/31, was obtained, which produced 427.5 U/ml xylanase. This value is 6.13-fold higher than that of the starting strain NRCF5 and 2.48-fold higher than that of the parent strain (mutant NEA51). The subculture experiments indicated that the high producer of marine Aspergillus sp. R4/31 fusant was stable.

A typical endo-xylanase from Streptomyces rameus L2001 and its unique characteristics in xylooligosaccharide production

The activity of the extracellular xylanase produced by Streptomyces rameus L2001 against different xylans and xylooligosaccharides (XOS) was investigated. The main products of hydrolysis of birchwood xylan and oat-spelt xylan by the S. rameus L2001 xylanase were xylobiose (X2) and xylotriose (X3), suggesting that this is an endo-acting xylanase. This was confirmed by analysis of XOS degradation products. The enzyme hardly hydrolyzed X2 and X3, but hydrolyzed xylotetraose (X4) and xylopentaose (X5) producing mainly X2 and X3 through transglycosylation. Depending on the substrate, different quantities of reducing sugars were produced by the xylanase: 150 mg/g from corncob, 105 mg/g from bean culms, and 133 mg/g from bagasse. With the bagasse substrate, the xylanase yielded 2.36, 2.76, 2.03, and 2.17 mg/mL of X2, X3, X4, and X5, respectively. The structure of xylobiose and xylotriose from the hydrolysis of corncob xylan was identified by MS and NMR. The production of XOS from various agricultural wastes has potential industrial applications. This is the first report of XOS production by S. rameus L2001.

Isolation, purification and characterisation of low molecular weight xylanase from Bacillus pumilus SSP-34

Low molecular weight endo-xylanase from Bacillus pumilus SSP-34 was purified to homogeneity using ion exchange and size exclusion chromatographies. Xylanases were isolated by novel purification protocol which includes the use of anion exchange matrix such as DEAE Sepharose CL 6B with less affinity towards enzyme protein. The purified B. pumilus SSP-34 have a molecular weight of 20 kDa, with optimum pH and temperature at 6.0 and 50 °C, respectively. The enzyme was stable at 50 °C for 30 min. It showed remarkable stability at pH values ranging from 4.5 to 9 when the reaction was carried out at 50 °C. K (m) and V (max) values, determined with oats spelts xylan were 6.5 mg ml⁻¹ and 1,233 μmol min⁻¹ mg⁻¹ protein, respectively, and the specific activity was 1,723 U mg⁻¹.

Purification and biochemical characterization of a highly thermostable xylanase from Actinomadura sp. strain Cpt20 isolated from poultry compost

An extracellular thermostable xylanase from a newly isolated thermophilic Actinomadura sp. strain Cpt20 was purified and characterized. Based on matrix-assisted laser desorption-ionization time-of-flight mass spectrometry analysis, the purified enzyme is a monomer with a molecular mass of 20,110.13 Da. The 19 residue N-terminal sequence of the enzyme showed 84% homology with those of actinomycete endoxylanases. The optimum pH and temperature values for xylanase activity were pH 10 and 80 °C, respectively. This xylanase was stable within a pH range of 5-10 and up to a temperature of 90 °C. It showed high thermostability at 60 °C for 5 days and half-life times at 90 °C and 100 °C were 2 and 1 h, respectively. The xylanase was specific for xylans, showing higher specific activity on soluble oat-spelt xylan followed by beechwood xylan. This enzyme obeyed the Michaelis-Menten kinetics, with the K (m) and k (cat) values being 1.55 mg soluble oat-spelt xylan/ml and 388 min(-1), respectively. While the xylanase from Actinomadura sp. Cpt20 was activated by Mn(2+), Ca(2+), and Cu(2+), it was, strongly inhibited by Hg(2+), Zn(2+), and Ba(2+). These properties make this enzyme a potential candidate for future use in biotechnological applications particularly in the pulp and paper industry.