Microbial xylanolytic enzyme system: properties and applications

Influence of Salinity on the Extracellular Enzymatic Activities of Marine Pelagic Fungi

Even though fungi are ubiquitous in the biosphere, the ecological knowledge of marine fungi remains rather rudimentary. Also, little is known about their tolerance to salinity and how it influences their activities. Extracellular enzymatic activities (EEAs) are widely used to determine heterotrophic microbes' enzymatic capabilities and substrate preferences. Five marine fungal species belonging to the most abundant pelagic phyla (Ascomycota and Basidiomycota) were grown under non-saline and saline conditions (0 g/L and 35 g/L, respectively). Due to their sensitivity and specificity, fluorogenic substrate analogues were used to determine hydrolytic activity on carbohydrates (β-glucosidase, β-xylosidase, and N-acetyl-β-D-glucosaminidase); peptides (leucine aminopeptidase and trypsin); lipids (lipase); organic phosphorus (alkaline phosphatase), and sulfur compounds (sulfatase). Afterwards, kinetic parameters such as maximum velocity (Vmax) and half-saturation constant (Km) were calculated. All fungal species investigated cleaved these substrates, but some species were more efficient than others. Moreover, most enzymatic activities were reduced in the saline medium, with some exceptions like sulfatase. In non-saline conditions, the average Vmax ranged between 208.5 to 0.02 μmol/g biomass/h, and in saline conditions, 88.4 to 0.02 μmol/g biomass/h. The average Km ranged between 1553.2 and 0.02 μM with no clear influence of salinity. Taken together, our results highlight a potential tolerance of marine fungi to freshwater conditions and indicate that changes in salinity (due to freshwater input or evaporation) might impact their enzymatic activities spectrum and, therefore, their contribution to the oceanic elemental cycles.

Organic matter stability and lability in terrestrial and aquatic ecosystems: A chemical and microbial perspective

Terrestrial and aquatic ecosystems have specific carbon fingerprints and sequestration potential, due to the intrinsic properties of the organic matter (OM), mineral content, environmental conditions, and microbial community composition and functions. A small variation in the OM pool can imbalance the carbon dynamics that ultimately affect the climate and functionality of each ecosystem, at regional and global scales. Here, we review the factors that continuously contribute to carbon stability and lability, with particular attention to the OM formation and nature, as well as the microbial activities that drive OM aggregation, degradation and eventually greenhouse gas emissions. We identified that in both aquatic and terrestrial ecosystems, microbial attributes (i.e., carbon metabolism, carbon use efficiency, necromass, enzymatic activities) play a pivotal role in transforming the carbon stock and yet they are far from being completely characterised and not often included in carbon estimations. Therefore, future research must focus on the integration of microbial components into carbon mapping and models, as well as on translating molecular-scaled studies into practical approaches. These strategies will improve carbon management and restoration across ecosystems and contribute to overcome current climate challenges.

Structural insights of a putative β-1,4-xylosidase (PsGH43F) of glycoside hydrolase family 43 from Pseudopedobacter saltans

Structural and conformational insights of a putative β-1,4-xylosidase (PsGH43F) of glycoside hydrolase family 43 from Pseudopedobacter saltans were investigated by computational and Circular Dichroism (CD) analyses. PsGH43F was cloned and expressed in E. coli BL21 (DE3) cells and the purified enzyme gave the size ~50 kDa on SDS-PAGE analysis. Multiple Sequence Alignment of PsGH43F sequence followed by superposition of modeled structure with homologous structures displayed the presence of three conserved catalytic amino acid residues, Asp33, Asp149 and Glu212. The secondary structure analysis by CD showed 2.72 % α-helix and 36.06 % β-strands. The homology modeled structure of PsGH43F displayed a 5-bladed β-propeller fold for catalytic module at N-terminal and a β-sandwich structure for CBM6 at the C-terminal. Ramachandran plot displayed 99.5 % of residues in the allowed regions. MD simulation of PsGH43F revealed the compactness and stability of the structure. Molecular docking studies of PsGH43F with xylo-oligosaccharides revealed its maximum binding affinity for xylobiose. MD simulation of PsGH43F-xylobiose complex confirmed the increased structural and conformational stability in presence of substrate. The Hydrodynamic diameter analysis of PsGH43F by DLS was in the range, 0.25-0.28 μm.

High-level production of xylose from agricultural wastes using GH11 endo-xylanase and GH43 β-xylosidase from Bacillus sp

As a promising feedstock, alkali-extracted xylan from lignocellulosic biomass is desired for producing xylose, which can be used for renewable biofuels production. In this study, an efficient pathway has been established for low-cost and high-yield production of xylose by hydrolysis of alkali-extracted xylan from agricultural wastes using an endo-1,4-xylanase (XYLA) from Bacillus safensis TCCC 111022 and a β-xylosidase (XYLO) from B. pumilus TCCC 11573. The optimum activities of recombinant XYLA (rXYLA) and XYLO (rXYLO) were 60 ℃ and pH 8.0, and 30 ℃ and pH 7.0, respectively. They were stable over a broad pH range (pH 6.0-11.0 and 7.0-10.0). rXYLO showed a relatively high xylose tolerance up to 100 mM. Furthermore, the yield of xylose from wheat straw, rice straw, corn stover, corncob and sugarcane bagasse by rXYLA and rXYLO was 63.77%, 71.76%, 68.55%, 53.81%, and 58.58%, respectively. This study demonstrated a strategy to produce xylose from agricultural wastes by integrating alkali-extracted xylan and enzymatic hydrolysis.

Mass spectrometry imaging of oligosaccharides following in situ enzymatic treatment of maize kernels

In recent years enzymatic treatment of maize has been utilized in the wet-milling process to increase the yield of extracted starch, proteins, and other constituents. One of the strategies to obtain this goal is to add enzymes that break down insoluble cell-wall polysaccharides which would otherwise entrap starch granules. Due to the high complexity of maize polysaccharides, this goal is not easily achieved and more knowledge about the substrate and enzyme performances is needed. To gather information of both enzyme performance and increase substrate understanding, a method was developed using mass spectrometry imaging (MSI) to analyze degradation products from polysaccharides following enzymatic treatment of the maize endosperm. Different enzymes were spotted onto cryosections of maize kernels which had been pre-treated with an amylase to remove starch. The cryosections were then incubated for 17 h. before mass spectrometry images were generated with a MALDI-MSI setup. The images showed varying degradation products for the different enzymes observed as pentose oligosaccharides differing with regards to sidechains and the number of linked pentoses. The method proved suitable for identifying the reaction products formed after reaction with different xylanases and arabinofuranosidases and for characterization of the complex arabinoxylan substrate in the maize kernel. HYPOTHESES: Mass spectrometry imaging can be a useful analytical tool for obtaining information of polysaccharide constituents and enzyme performance from maize samples.

Contributions and characteristics of two bifunctional GH43 β-xylosidase /α-L-arabinofuranosidases with different structures on the xylan degradation of Paenibacillus physcomitrellae strain XB

Xylan is one of the major polymeric hemicellulosic constituents of lignocellulosic biomass, and its effective utilization by microorganisms is crucial for the economical production of biofuels. In this study, Paenibacillus physcomitrellae XB exhibited different xylan degradation ability on different substrates of corncob xylan (CCX), oat spelt xylan (OSX), wheat flour arabinoxylan (AX) and beech wood xylan (BWX). The RT-QPCR result showed that two genes (Pph_0602 and Pph_2344) belonging to the glycoside hydrolase family 43 were up-regulated more than 5-fold on CCX and xylose. Substrate-specific assays with purified proteins Ppxyl43A (Pph_0602) and Ppxyl43B (Pph_2344) revealed that both exhibited β-xylosidase activity toward the chromogenic substrate p-nitrophenyl-β-D-xylopyranoside, and α-L-arabinofuranosidase activity toward p-nitrophenyl-α-L-arabinofuranoside, indicating their bifunctionality. By testing their degradation characteristics on different natural substrates, it was found that both Ppxyl43A and Ppxyl43B showed similar degradation ability on CCX and OSX. Both enzymes could hydrolyze xylohexaose and xylobiose completely to xylose, but could not hydrolyze BWX and AX, suggesting they mainly hydrolyze xylo-oligosaccharides by β-xylosidase activity. Further analysis showed that both of them displayed very high pH stability and thermostability on the β-xylosidase activity, but Ppxy143B exhibited wider pH and temperature ranges, higher pH and temperature stability, was less influenced by metal ions, and had a slower start-up response than Ppxyl43A. Given their predicted structure, it is likely that the enzymatic differences between Ppxyl43A and Ppxyl43B might be related to the extra C-terminus domain (GH43_C2) in Ppxyl43B, which could enhance the enzymatic stability while restricting the substrates' or metal ions' access to the active sites of Ppxyl43B. In conclusion, both Ppxyl43A and Ppxyl43B were β-xylosidase/α-L-arabinofuranosidase bifunctional enzymes and might be useful in xylan biomass conversion, especially in the hydrolysis of xylo-oligosaccharides into xylose.

Xylan Decomposition in Plant Cell Walls as an Inducer of Surfactin Synthesis by Bacillus subtilis

Hemicellulose is the second most abundant plant heterogenous biopolymer. Among products obtained from a wide range of agro-residues, biosurfactants, e.g., surfactin (SU), are gaining increasing interest. Our previous studies have shown that a Bacillus subtilis strain can successfully produce a significant amount of SU using a rapeseed cake. This work aimed to investigate plant hemicellulose components as substrates promoting SU's efficient production by B. subtilis 87Y. Analyses of SU production, enzymatic activity and cell wall composition of hulled oat caryopses suggest that the main ingredients of plant hemicellulose, in particular xylan and its derivatives, may be responsible for an increased biosurfactant yield.

Screening of multimeric β-xylosidases from the gut microbiome of a higher termite, Globitermes brachycerastes

Termite gut microbiome is a rich reservoir for glycoside hydrolases, a suite of enzymes critical for the degradation of lignocellulosic biomass. To search for hemicellulases, we screened 12,000 clones from a fosmid gut library of a higher termite, Globitermes brachycerastes. As a common Southeastern Asian genus, Globitermes distributes predominantly in tropical rain forests and relies on the lignocellulases from themselves and bacterial symbionts to digest wood. In total, 22 positive clones with β-xylosidase activity were isolated, in which 11 representing different restriction fragment length polymorphism (RFLP) patterns were pooled and subjected to 454 pyrosequencing. As a result, eight putative β-xylosidases were cloned and heterologously expressed in Escherichia coli BL21 competent cells. After purification using Ni-NTA affinity chromatography, recombinant G. brachycerastes symbiotic β-xylosidases were characterized enzymatically, including their pH and temperature optimum. In addition to β-xylosidase activity, four of them also exhibited either β-glucosidase or α-arabinosidases activities, suggesting the existence of bifunctional hemicellulases in the gut microbiome of G. brachycerastes. In comparison to multimeric protein engineering, the involvement of naturally occurring multifunctional biocatalysts streamlines the genetic modification procedures and simplifies the overall production processes. Alternatively, these multimeric enzymes could serve as the substitutes for β-glucosidase, β-xylosidase and α-arabinosidase to facilitate a wide range of industrial applications, including food processing, animal feed, environment and waste management, and biomass conversion.

Synergistic hydrolysis of xylan using novel xylanases, β-xylosidases, and an α-L-arabinofuranosidase from Geobacillus thermodenitrificans NG80-2

Lignocellulosic biomass from various types of wood has become a renewable resource for production of biofuels and biobased chemicals. Because xylan is the major component of wood hemicelluloses, highly efficient enzymes to enhance xylan hydrolysis can improve the use of lignocellulosic biomass. In this study, a xylanolytic gene cluster was identified from the crude oil-degrading thermophilic strain Geobacillus thermodenitrificans NG80-2. The enzymes involved in xylan hydrolysis, which include two xylanases (XynA1, XynA2), three β-xylosidases (XynB1, XynB2, XynB3), and one α-L-arabinofuranosidase (AbfA), have many unique features, such as high pH tolerance, high thermostability, and a broad substrate range. The three β-xylosidases were highly resistant to inhibition by product (xylose) accumulation. Moreover, the combination of xylanase, β-xylosidase, and α-L-arabinofuranosidase exhibited the largest synergistic action on xylan degradation (XynA2, XynB1, and AbfA on oat spelt or beechwood xylan; XynA2, XynB3, and AbfA on birchwood xylan). We have demonstrated that the proposed enzymatic cocktail almost completely converts complex xylan to xylose and arabinofuranose and has great potential for use in the conversion of plant biomass into biofuels and biochemicals.

Strategies for improved isopropanol-butanol production by a Clostridium strain from glucose and hemicellulose through consolidated bioprocessing

BACKGROUND

High cost of traditional substrates and formation of by-products (such as acetone and ethanol) in acetone-butanol-ethanol (ABE) fermentation hindered the large-scale production of biobutanol. Here, we comprehensively characterized a newly isolated solventogenic and xylanolytic Clostridium species, which could produce butanol at a high ratio with elimination of ethanol and conversion of acetone to more value-added product, isopropanol. Ultimately, direct butanol production from hemicellulose was achieved with efficient expression of indigenous xylanase by the novel strain via consolidated bioprocessing.

RESULTS

A novel wild-type Clostridium sp. strain NJP7 was isolated and characterized in this study, which was capable of fermenting monosaccharides, e.g., glucose into butanol via a fermentative acetone-isopropanol-butanol pathway. With enhancement of buffering capacity and alcohol dehydrogenase activities, butanol and isopropanol titer by Clostridium sp. strain NJP7 was improved to 12.21 and 1.92 g/L, respectively, and solvent productivity could be enhanced to 0.44 g/L/h. Furthermore, with in situ extraction with biodiesel, the amount of butanol and isopropanol was finally improved to 25.58 and 5.25 g/L in the fed-batch mode. Meanwhile, Clostridium sp. strain NJP7 shows capability of direct isopropanol-butanol production from hemicelluloses with expression of indigenous xylanase. 2.06 g/L of butanol and 0.54 g/L of isopropanol were finally achieved through the temperature-shift simultaneous saccharification and fermentation, representing the highest butanol production directly from hemicellulose.

CONCLUSION

The co-production of isopropanol with butanol by the newly isolated Clostridium sp. strain NJP7 would add on the economical values for butanol fermentation. Furthermore, the high isopropanol-butanol production with in situ extraction would also greatly enhance the economic feasibility for fermentative production of butanol-isopropanol in large scale. Meanwhile, its direct production of butanol-isopropanol from polysaccharides, hemicellulose through secretion of indigenous thermostable xylanase, shows great potential using lignocellulosic wastes for biofuel production.

Characterization of a thermostable xylanase from a newly isolated Kluyvera species and its application for biobutanol production

Kluyvera species strain OM3 isolated from spent mushroom substrate could produce a high level of cellulase-free xylanase (5.12 U/mL). This xylanase showed maximum activities at 70 °C and pH 8.0, which could retain 100% and 71% activity after 1h incubation at 60 °C and 70 °C, and maintain stability over a wide range of pHs (5.0-9.0), indicating its thermal and pH stability. Moreover, the xylanase could hydrolyze untreated lignocellulosics (e.g., palm oil fiber) to reducing sugars with a yield of 27.1-46.9 mg/g. A co-culture consisting of Kluyvera sp. strain OM3 and Clostridium sp. strain BOH3 could directly convert birchwood xylan to 1.2g/L butanol, which was comparable to the amount of butanol (1.7 g/L) generated via separate hydrolysis by the xylanase and fermentation by Clostridium sp. strain BOH3. This is the first report on the production, characterization of a xylanase from genus Kluyvera and its application for butanol production directly from hemicelluloses.

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.

Determination of some significant batch culture conditions affecting acetyl-xylan esterase production by Penicillium notatum NRRL-1249

Background

Acetyl-xylan esterase (AXE, EC 3.1.1.72) hydrolyses acetate group from the linear chain of xylopyranose residues bound by β-1,4-linkage. The enzyme finds commercial applications in bio-bleaching of wood pulp, treating animal feed to increase digestibility, processing food to increase clarification and converting lignocellulosics to feedstock and fuel. In the present study, we report on the production of an extracellular AXE from Penicillium notatum NRRL-1249 by solid state fermentation (SSF).

Results

Wheat bran at a level of 10 g (with 4 cm bed height) was optimized as the basal substrate for AXE production. An increase in enzyme activity was observed when 7.5 ml of mineral salt solution (MSS) containing 0.1% KH₂PO₄, 0.05% KCl, 0.05% MgSO₄.7H₂O, 0.3% NaNO₃, 0.001% FeSO₄.2H₂O and 0.1% (v/w) Tween-80 as an initial moisture content was used. Various nitrogen sources including ammonium sulphate, urea, peptone and yeast extract were compared for enzyme production. Maximal enzyme activity of 760 U/g was accomplished which was found to be highly significant (p ≤ 0.05). A noticeable enhancement in enzyme activity was observed when the process parameters including incubation period (48 h), initial pH (5), 0.2% (w/w) urea as nitrogen source and 0.5% (v/w) Tween-80 as a stimulator were further optimized using a 2-factorial Plackett-Burman design.

Conclusion

From the results it is clear that an overall improvement of more than 35% in terms of net enzyme activity was achieved compared to previously reported studies. This is perhaps the first report dealing with the use of P. notatum for AXE production under batch culture SSF. The Plackett-Burman model terms were found highly significant (HS), suggesting the potential commercial utility of the culture used (df = 3, LSD = 0.126).

Biochemical and molecular characterization of thermo-alkali tolerant xylanase producing bacteria from thermal springs of Manikaran

One hundred ten alkalo-tolerant thermophilic bacteria were isolated from 17 samples (water and sediment) collected from Manikaran. Of 110 isolates, 70 showed the production of xylanases and were further screened for growth and production of xylanases at different temperature ranging from 40 to 75°C. Eleven isolates that showed growth and xylanase production at temperatures ≥50°C were selected for quantitative estimation in modified Reese mineral liquid medium containing wheat bran. Maximum xylanase activity was produced by isolate H-7 followed by H-9 and R-9 and was statistically superior to other isolates. The microscopic observation showed that the isolates possessed the typical rod with endospore, characteristic of genus Bacillus. The isolates were found to be oxidase and catalase positive. Using BIOLOG Microlog 3 software, the isolates H7, H9 and R9 were identified as Paenibacillus ehemensis, Bacillus cereus/B. thuringiensis and B. subtilis respectively, based on utilization of 95 carbon sources. PCR-RFLP analysis of 16S rDNA indicated that the isolates were genetically different from each other. DNA sequencing of the three isolates and phylogenetic analysis revealed that all the isolates obtained from Manikaran thermal springs showed 97 to 100% similarity with the sequences within the GenBank. The closest phylogenetic neighbours according to the 16S rRNA gene sequence data for the three isolates H-7, H-9, and R-9 were Paenibacillus ehemensis, Bacillus cereus and Bacillus subtilis, respectively.

'Single lay out' and 'mixed lay out' enzymatic processes for bio-bleaching of kraft pulp

Xylanase alone as 'single lay out' (strategy I) and in combination with pectinase as 'mixed lay out' (strategy II) was used to investigate their bio-bleaching potentials. Strategy I was carried at 70 degrees C using 5 U/g of xylanase at pH 9.5 and 12.5 whereas strategy II was carried out at 70 degrees C using 5 U/g of each of the enzyme, respectively at pH 9.5. Bio-bleaching caused 15% and 20% less Cl(2) consumption though strategy I and II, respectively over chemical bleaching. Strategy II was proved to be 35.71% more efficient in ClO(2) saving than conventional method. Significant improvement in various pulp properties viz. tensile strength 25.70%, breaking length 21.80%, burst factor 20.00%, burstness 13.86%, tear factor 6.61% and tearness 18.88%, was also observed through 'mixed lay out' strategy.

Biochemical characterization of a novel dual-function arabinofuranosidase/xylosidase isolated from a compost starter mixture

The gene encoding a glycoside hydrolase family 43 enzyme termed deAX was isolated and subcloned from a culture seeded with a compost starter mixed bacterium population, expressed with a C-terminal His(6)-tag, and purified to apparent homogeneity. deAX was monomeric in solution and had a broad pH maximum between pH 5.5 and pH 7. A twofold greater k (cat)/K (m) for the p-nitrophenyl derivative of alpha-L: -arabinofuranose versus that for the isomeric substrate beta-D-xylopyranose was due to an appreciably lower K (m) for the arabinofuranosyl substrate. Substrate inhibition was observed for both 4-methylumbelliferryl arabinofuranoside and the xylopyranoside cogener. While no loss of activity was observed over 4 h at 40 degrees C, the observed t (1/2) value rapidly decreased from 630 min at 49 degrees C to 47 min at 53 degrees C. The enzyme exhibited end-product inhibition, with a K (i) for xylose of 145 mM, 18.5 mM for arabinose, and 750 mM for glucose. Regarding natural substrate specificity, deAX had arabinofuranosidase activity on sugar beet arabinan, 1,5-alpha-L-arabinobiose, and 1,5-alpha-L-arabinotriose, and wheat and rye arabinoxylan, while xylosidase activity was detected for the substrates xylobiose, xylotriose, xylotetraose, and arabinoxylan from beech and birch. Thus, deAX can be classified as a dual-function xylosidase/arabinofuranosidase with respect to both artificial and natural substrate specificity.

Purification and characterization of extracellular xylanase from Streptomyces cyaneus SN32

Streptomyces cyaneus SN32 was used in this study to produce extracellular xylanase, an important industrial enzyme used in pulp and paper industry. The enzyme was purified to homogeneity by ammonium sulfate precipitation followed by anion exchange chromatography using DEAE-Sepharose column, with 43.0% yield. The enzyme was found to be a monomer of 20.5 kDa as determined by SDS gel electrophoresis and has a pI of 8.5. The optimum pH and temperature for purified xylanase activity was 6.0 and 60-65 degrees C, respectively. The half-lives of xylanase at 50 and 65 degrees C were approximately 200 and 50 min, respectively. The xylanase exhibited K(m) and V(max) values of 11.1 mg/ml and 45.45 micromol/min/mg. The 15 residue N-terminal sequence of the enzyme was found to be 87% identical up to that of endoxylanases from Steptomyces sp. Based on the zymogram analysis, sequence similarity and other characteristics, it is proposed that the purified enzyme from S. cyaneus SN32 is an endoxylanase and belongs to Group 1 xylanases (low molecular weight - basic proteins). The purified enzyme was stable for more than 20 week at 4 degrees C. Easy purification from the fermentation broth and its high stability will be highly useful for industrial application of this endoxylanase.

Characterization of beta-xylosidase enzyme from a Pichia stipitis mutant

beta-Xylosidase production was maximal for the mutant Pichia stipitis NP54376 grown on xylan as the sole carbon source. beta-Xylosidase was purified from culture supernatant by (NH(4))(2)SO(4) precipitation and a hydrophobic interaction chromatography on phenyl sepharose. Optima of pH and temperature were 5.0 and 50 degrees C, respectively. The enzyme was inhibited by 2-mercaptoethanol (100%) and Fe(3+) (80%), and moderately affected by Cu(2+), Ag(+), NH(4)(+) and Mg(2+) and SDS. The purified xylosidase hydrolyzed xylobiose and xylo-oligosaccharides and it did not exhibit activity against cellulose, starch, maltose and cellobiose. 2.5 g l(-1) glucose repressed beta-xylosidase activity in the NP54376 strain. The K(m) and V(max) values on p-nitrophenyl-beta-xylopyranoside were 1.6 mM and 186 micromol p-nitrophenyl min(-1)mg(-1) protein, respectively. Analysis of the hydrolysis products by HPLC indicated that the major hydrolysis product is xylobiose in all the carbon sources tested.

Production of cellulase-free endoxylanase from novel alkalophilic thermotolerent Bacillus pumilus by solid-state fermentation and its application in wastepaper recycling

The present study aimed at optimization of culture condition for the enhanced production of extra cellular thermostable cellulase-free xylanase from Bacillus pumilus by solid-state fermentation. Batch studies were carried out to evaluate various agro-industrial residues such as rice bran, rice husk, rice straw, sawdust, coconut pith, sugarcane bagasse and wheat bran for enzyme production by the bacterial culture. The endoxylanase production was highest on wheat bran media (5582 U/gds), which was enhanced 3.8-fold (21,431 U/gds) by optimization of cultivation conditions. The enzymatic extracts was used in mixed wastepaper recycling, which resulted in a considerable improvement of the paper strength with high drainage and easy drying up. The results of enzyme application with recycled paper clearly indicated that the effective use of enzymes in fiber separation could reduce the cost of carton paper production.

Cloning and characterization of a cold-active xylanase enzyme from an environmental DNA library

There is a great interest in xylanases due to the wide variety of industrial applications for these enzymes. We cloned a xylanase gene (xyn8) from an environmental genomic DNA library. The encoded enzyme was predicted to be 399 amino acids with a molecular weight of 45.9 kD. The enzyme was categorized as a glycosyl hydrolase family 8 member based on sequence analysis of the putative catalytic domain. The purified enzyme was thermolabile, had an activity temperature optimum of 20 degrees C on native xylan substrate, and retained significant activity at lower temperatures. At 4 degrees C, the apparent K (m) was 3.7 mg/ml, and the apparent k (cat) was 123/s.

Isolation and Characterization of a Cold-Active Xylanase Enzyme from Flavobacterium sp

Xylan is the major component of hemicellulose, and xylan should be fully utilized to improve the efficiencies of a biobased economy. There are a variety of industrial reaction conditions in which an active xylanase enzyme would be desired. As a result, xylanase enzymes with different activity profiles are of great interest. We isolated a xylanase gene (xyn10) from a Flavobacterium sp. whose sequence suggests that it is a glycosyl hydrolase family 10 member. The enzyme has a temperature optimum of 30 degrees C, is active at cold temperatures, and is thermolabile. The enzyme has an apparent Km of 1.8 mg/ml and kcat of 100 sec-1 for beechwood xylan, attacks highly branched native xylan substrates, and does not have activity against glucans.

Solid-state fermentation systems-an overview

Starting with a brief history of solid-state fermentation (SSF), major aspects of SSF are reviewed, which include factors affecting SSF, biomass, fermentors, modeling, industrial microbial enzymes, organic acids, secondary metabolites, and bioremediation. Physico-chemical and environmental factors such as inoculum type, moisture and water activity, pH, temperature, substrate, particle size, aeration and agitation, nutritional factors, and oxygen and carbon dioxide affecting SSF are reviewed. The advantages of SSF over Submerged Fermentation (SmF) are indicated, and the different types of fermentors used in SSF described. The economic feasibilities of adopting SSF technology in the commercial production of industrial enzymes such as amylases, cellulases, xylanase, proteases, phytases, lipases, etc., organic acids such as citric acid and lactic acid, and secondary metabolites such as gibberellic acid, ergot alkaloids, and antibiotics such as penicillin, cyclosporin, cephamycin and tetracyclines are highlighted. The relevance of applying SSF technology in the production of mycotoxins, biofuels, and biocontrol agents is discussed, and the need for adopting SSF technology in bioremediation of toxic compounds, biological detoxication of agro-industrial residues, and biotransformation of agro-products and residues is emphasized.

Cloning and Characterization of the Xyn11A Gene from Lentinula edodes

Hemicellulose represents a rich source of biomass that can be converted into useful chemical feedstocks. One of the main components of hemicellulose is xylan, a polymer of xylose residues. Xylanase enzymes that hydrolyze xylan are therefore of great commercial interest. We have cloned a gene (xyn11A) that encodes a 283-amino acid xylanase enzyme from the fungus Lentinula edodes. The enzyme has a pI of 4.6 and belongs to the highly conserved glycosyl hydrolase family 11. The xylanase gene was cloned into a Pichia pastoris expression vector that secretes active enzyme into both solid and liquid media. The optimal reaction conditions were at pH 4.5 and 50 degrees C. The enzyme had a Km of 1.5 mg/ml and a Vmax of 2.1 mmol/min/mg. Xyn11A produced primarily xylobiose, xylotriose, and xylotetraose from a birchwood xylan substrate. This is the first report on the cloning of a hemicellulase gene from L. edodes.

Developments in the use of Bacillus species for industrial production

Bacillus species continue to be dominant bacterial workhorses in microbial fermentations. Bacillus subtilis (natto) is the key microbial participant in the ongoing production of the soya-based traditional natto fermentation, and some Bacillus species are on the Food and Drug Administration's GRAS (generally regarded as safe) list. The capacity of selected Bacillus strains to produce and secrete large quantities (20-25 g/L) of extracellular enzymes has placed them among the most important industrial enzyme producers. The ability of different species to ferment in the acid, neutral, and alkaline pH ranges, combined with the presence of thermophiles in the genus, has lead to the development of a variety of new commercial enzyme products with the desired temperature, pH activity, and stability properties to address a variety of specific applications. Classical mutation and (or) selection techniques, together with advanced cloning and protein engineering strategies, have been exploited to develop these products. Efforts to produce and secrete high yields of foreign recombinant proteins in Bacillus hosts initially appeared to be hampered by the degradation of the products by the host proteases. Recent studies have revealed that the slow folding of heterologous proteins at the membrane-cell wall interface of Gram-positive bacteria renders them vulnerable to attack by wall-associated proteases. In addition, the presence of thiol-disulphide oxidoreductases in B. subtilis may be beneficial in the secretion of disulphide-bond-containing proteins. Such developments from our understanding of the complex protein translocation machinery of Gram-positive bacteria should allow the resolution of current secretion challenges and make Bacillus species preeminent hosts for heterologous protein production. Bacillus strains have also been developed and engineered as industrial producers of nucleotides, the vitamin riboflavin, the flavor agent ribose, and the supplement poly-gamma-glutamic acid. With the recent characterization of the genome of B. subtilis 168 and of some related strains, Bacillus species are poised to become the preferred hosts for the production of many new and improved products as we move through the genomic and proteomic era.