Characterization and identification of the xylanolytic enzymes from Aspergillus fumigatus Z5

Characterization of a highly thermostable recombinant xylanase from Anoxybacillus ayderensis

Xylanases are the main enzymes to hydrolyze xylan, the major hemicellulose found in lignocellulose. Xylanases also have a wide range of industrial applications. Therefore, the discovery of new xylanases has the potential to enhance efficiency and sustainability in many industries. Here, we report a xylanase with thermophilic character and superior biochemical properties for industrial use. The new xylanase is discovered in Anoxybacillus ayderensis as an intracellular xylanase (AAyXYN329) and recombinantly produced. While AAyXYN329 shows significant activity over a wide pH and temperature range, optimum activity conditions were determined as pH 6.5 and 65 °C. The half-life of the enzyme was calculated as 72 h at 65 °C. The enzyme did not lose activity between pH 6.0-9.0 at +4 °C for 75 days. Km, kcat and kcat/Km values of AAyXYN329 were calculated as 4.09824 ± 0.2245 μg/μL, 96.75 1/sec, and 23.61/L/g.s -1, respectively. In conclusion, the xylanase of A. ayderensis has an excellent potential to be utilized in many industrial processes.

Enhancing the acid stability of the recombinant GH11 xylanase xynA through N-terminal substitution to facilitate its application in apple juice clarification

The utilization of xylanase in juice clarification is contingent upon its stability within acidic environments. We generated a mutant xynA-1 by substituting the N-terminal segment of the recombinant xylanase xynA to investigate the correlation between the N-terminal region of xylanase and its acid stability. The enzymatic activity of xynA-1 was found to be superior under acidic conditions (pH 5.0). It exhibited enhanced acid stability, surpassing the residual enzyme activity values of xynA at pH 4.0 (53.07 %), pH 4.5 (69.8 %), and pH 5.0 (82.4 %), with values of 60.16 %, 77.74 %, and 87.3 %, respectively. Additionally, the catalytic efficiency of xynA was concurrently improved. Through molecular dynamics simulation, we observed that N-terminal shortening induced a reduction in motility across most regions of the protein structure while enhancing its stability, particularly Lys131-Phe146 and Leu176-Gly206. Furthermore, the application of treated xynA-1 in the process of apple juice clarification led to a significant increase in clarity within a short duration of 20 min at 35 °C while ensuring the quality of the apple juice. This study not only enhances the understanding of the N-terminal region of xylanase but also establishes a theoretical basis for augmenting xylanase resources employed in fruit juice clarification.

Mixed food waste valorization using a thermostable glucoamylase enzyme produced by a newly isolated filamentous fungus: A sustainable biorefinery approach

Food waste is a lucrative source of complex nutrients, which can be transformed into a multitude of bioproducts by the aid of microbial cell factories. The current study emphasizes isolating Glucoamylase enzyme (GA) producing strains that can effectively break down mixed food waste (MW), which serves as a substrate for biomanufacturing. The screening procedure relied heavily on the growth of isolated fungi on starch agar media, to specifically identify the microbes with the highest starch hydrolysis potential. A strain displayed the highest GA activity of 2.9 ± 0.14 U/ml which was selected and identified as Aspergillus fumigatus via molecular methods of identification. Exposure of the A. fumigatus with 200 mM Ethyl methanesulphonate (EMS) led to a 23.79% increase compared to the wild-type GA. The growth conditions like cultivation temperature or the number of spores in the inoculum were investigated. Further, maximum GA activity was exhibited at pH 5, 55 °C, and at 5 mM Ca2+ concentration. The GA showed thermostability, retaining activity even after long periods of exposure to temperatures as high as 95 °C. The improvement of hydrolysis of MW was achieved by Taguchi design where a maximum yield of 0.57 g g-1 glucose was obtained in the hydrolysate. This study puts forth the possibility that mixed food waste, despite containing spices and other microbial growth-inhibitory substances, can be efficiently hydrolyzed to release glucose units, by robust fungal cell factories. The glucose released can then be utilized as a carbon source for the production of value-added products.

Clustered surface amino acid residues modulate the acid stability of GH10 xylanase in fungi

Acidic xylanases are widely used in industries such as biofuels, animal feeding, and fruit juice clarification due to their tolerance to acidic environments. However, the factors controlling their acid stability, especially in GH10 xylanases, are only partially understood. In this study, we identified a series of thermostable GH10 xylanases with optimal temperatures ranging from 70 to 90 °C, and among these, five enzymes (Xyn10C, Xyn10RE, Xyn10TC, Xyn10BS, and Xyn10PC) exhibited remarkable stability at pH 2.0. Our statistical analysis highlighted several factors contributing to the acid stability of GH10 xylanases, including electrostatic repulsion, π-π stacking, ionic bonds, hydrogen bonds, and Van der Waals interactions. Furthermore, through mutagenesis studies, we uncovered that acid stability is influenced by a complex interplay of amino acid residues. The key amino acid sites determining the acid stability of GH10 xylanases were thus elucidated, mainly concentrated in two surface regions behind the enzyme active center. Notably, the critical residues associated with acid stability markedly enhanced Xyn10RE's thermostability by more than sixfold, indicating a potential acid-thermal interplay in GH10 xylanases. This study not only reported a series of valuable genes but also provided a range of modification targets for enhancing the acid stability of GH10 xylanases. KEY POINTS: • Five acid stable and thermostable GH10 xylanases were reported. • The key amino acid sites, mainly forming two enriched surface regions behind the enzyme active center, were identified responsible for acid stability of GH10 xylanases. • The finding revealed interactive amino acid sites, offering a pathway for synergistic enhancement of both acid stability and thermostability in GH10 xylanase modifications.

A multifaceted enzyme conspicuous in fruit juice clarification: An elaborate review on xylanase

Xylanase enzyme has been classified as an enzyme belonging to the glycoside hydrolase family. The catalytic action of xylanase is focused on the degradation of xylan, a substrate for this enzyme comprising of a complex arrangement of monosaccharides interlinked with the help of ester and glycosidic bonds. Xylan represents the second most profuse renewable polysaccharide present on earth. Breakage of the β- 1, 4-glycoside linkage in the xylan polymer is what makes xylanase enzyme an important biocatalyst favoring various applications including treatment of pulp for improving paper quality, improvement of bread quality, treatment of lignocelluloses waste, production of xylose sugar and production of biological fuels. Most recently, xylanase has been exploited in the food industry for the purpose of fruit juice clarification. Turbidity caused by the colloidal polysaccharides present in the freshly squeezed fruit juice poses a setback to the fruit juice industry since the commercial product must be clear and free of excess polysaccharides to improve juice quality and storage life. This review gives an overview of the recent advancements made in regards to xylanase enzyme being used commercially with main focus on its role in fruit juice clarification.

Aspergillus sp. A31 and Curvularia geniculata P1 mitigate mercury toxicity to Oryza sativa L

Aspergillus sp. A31 and Curvularia geniculata P1 are endophytes that colonize the roots of Aeschynomene fluminensis Vell. and Polygonum acuminatum Kunth. in humid environments contaminated with mercury. The two strains mitigated mercury toxicity and promoted Oryza sativa L growth. C. geniculata P1 stood out for increasing the host biomass by fourfold and reducing the negative effects of the metal on photosynthesis. Assembling and annotation of Aspergillus sp. A31 and C. geniculata P1 genomes resulted in 28.60 Mb (CG% 53.1; 10,312 coding DNA sequences) and 32.92 Mb (CG% 50.72; 8,692 coding DNA sequences), respectively. Twelve and 27 genomes of Curvularia/Bipolaris and Aspergillus were selected for phylogenomic analyzes, respectively. Phylogenetic analysis inferred the separation of species from the genus Curvularia and Bipolaris into different clades, and the separation of species from the genus Aspergillus into three clades; the species were distinguished by occupied niche. The genomes had essential gene clusters for the adaptation of microorganisms to high metal concentrations, such as proteins of the phytoquelatin-metal complex (GO: 0090423), metal ion binders (GO: 0046872), ABC transporters (GO: 0042626), ATPase transporters (GO: 0016887), and genes related to response to reactive oxygen species (GO: 0000302) and oxidative stress (GO: 0006979). The results reported here help to understand the unique regulatory mechanisms of mercury tolerance and plant development.

Purification, Identification, and Characterization of a Glycoside Hydrolase Family 11-Xylanase with High Activity from Aspergillus niger VTCC 017

Xylanases (EC 3.2.1.8) have been considered as a potential green solution for the sustainable development of a wide range of industries including pulp and paper, food and beverages, animal feed, pharmaceuticals, and biofuels because they are the key enzymes that degrade the xylosidic linkages of xylan, the major component of the second most abundant raw material worldwide. Therefore, there is a critical need for the industrialized xylanases which must have high specific activity, be tolerant to organic solvent or detergent and be active during a wide range of conditions, such as high temperature and pH. In this study, an extracellular xylanase was purified from the culture broth of Aspergillus niger VTCC 017 for primary structure determination and properties characterization. The successive steps of purification comprised centrifugation, Sephadex G-100 filtration, and DEAE-Sephadex chromatography. The purified xylanase (specific activity reached 6596.79 UI/mg protein) was a monomer with a molecular weight of 37 kDa estimating from SDS electrophoresis. The results of LC/MS suggested that the purified protein is indeed an endo-1,4-β-D-xylanase. The purified xylanase showed the optimal temperature of 55 °C, and pH 6.5 with a stable xylanolytic activity within the temperature range of 45-50 °C, and within the pH range of 5.0-8.0. Most divalent metal cations including Zn²⁺, Fe²⁺, Mg²⁺, Cu²⁺, Mn²⁺ showed some inhibition of xylanase activity while the monovalent metal cations such as K⁺ and Ag⁺ exhibited slight stimulating effects on the enzyme activity. The introduction of 10-30% different organic solvents (n-butanol, acetone, isopropanol) and several detergents (Triton X-100, Tween 20, and SDS) slightly reduced the enzyme activity. Moreover, the purified xylanase seemed to be tolerant to methanol and ethanol and was even stimulated by Tween 80. Overall, with these distinctive properties, the putative xylanase could be a successful candidate for numerous industrial uses.

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

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

Current Practices for Reference Gene Selection in RT-qPCR of Aspergillus: Outlook and Recommendations for the Future

Aspergillus is a genus of filamentous fungi with vast geographic and ecological distributions. Species within this genus are clinically, agriculturally and biotechnologically relevant, leading to increasing interest in elucidating gene expression dynamics of key metabolic and physiological processes. Reverse-transcription quantitative Polymerase Chain Reaction (RT-qPCR) is a sensitive and specific method of quantifying gene expression. A crucial step for comparing RT-qPCR results between strains and experimental conditions is normalisation to experimentally validated reference gene(s). In this review, we provide a critical analysis of current reference gene selection and validation practices for RT-qPCR gene expression analyses of Aspergillus. Of 90 primary research articles obtained through our PubMed query, 17 experimentally validated the reference gene(s) used. Twenty reference genes were used across the 90 studies, with beta-tubulin being the most used reference gene, followed by actin, 18S rRNA and glyceraldehyde 3-phosphate dehydrogenase. Sixteen of the 90 studies used multiple reference genes for normalisation. Failing to experimentally validate the stability of reference genes can lead to conflicting results, as was the case for four studies. Overall, our review highlights the need to experimentally validate reference genes in RT-qPCR studies of Aspergillus.

Isolation, Identification and In Silico Study of Native Cellulase Producing Bacteria

Aims:

The purpose of this study was to screen the bacteria producing cellulase enzymes and their bioinformatics studies.

Background:

Cellulose is a long-chain polymer of glucose that hydrolyzes by cellulases to glucose molecules. In order to design the new biotechnological applications, some strategies have been used as increasing the efficiency of enzyme production, generating cost-effective enzymes, producing stable enzymes and identification of new strains.

Objective:

On the other hand, some bacteria special features have made them suitable candidates for the identification of the new source of enzymes. In this regard, some native strains of bacteria were screened.

Methods:

These bacteria were grown on a culture containing the liquid M9 media containing CMC to ensure the synthesis of cellulase. The formation of a clear area in the culture medium indicated decomposition of cellulose. In the following, the DNA of these bacteria were extracted and their 16S rDNA genes were amplified.

Result:

The results show that nine samples were able to synthesize cellulase. In following, these strains were identified using 16S rDNA. The results show that these screened bacteria belonged to the Bacillus sp., Alcaligenes sp., Alcaligenes sp., and Enterobacter sp.

Conclusion:

The enzyme activity analysis shows that the Bacillus toyonensis, Bacillus sp. strain XA15-411 Bacillus cereus have produced the maximum yield of cellulases. However, these amounts of enzyme production in these samples are not proportional to their growth rate. As the bacterial growth chart within 4 consecutive days shows that the Alcaligenes sp. Bacillus cereus, Bacillus toyonensis, Bacillus sp. strain XA15-411 have a maximum growth rate. The study of the phylogenetic tree also shows that Bacillus species are more abundant in the production of cellulase enzyme. These bioinformatics analyses show that the Bacillus species have different evolutionary relationships and evolved in different evolutionary time. However, for maximum cellulase production by this bacteria, some information as optimum temperature, optimum pH, carbon and nitrogen sources are needed for the ideal formulation of media composition. The cellulase production is closely controlled in microorganisms and the cellulase yields appear to depend on a variety of factors. However, the further studies are needed for cloning, purification and application of these new microbial cellulases in the different commercial fields as in food, detergent, and pharmaceutical, paper, textile industries and also various chemical industries. However, these novel enzymes can be further engineered through rational design or using random mutagenesis techniques.

Effect of Oligosaccharide Degree of Polymerization on the Induction of Xylan-Degrading Enzymes by Fusarium oxysporum f. sp. Lycopersici

Xylan is one of the most abundant carbohydrates on Earth. Complete degradation of xylan is achieved by the collaborative action of endo-β-1,4-xylanases and β-d-xylosidases and a number of accessories enzymes. In filamentous fungi, the xylanolytic system is controlled through induction and repression. However, the exact mechanism remains unclear. Substrates containing xylan promote the induction of xylanases, which release xylooligosaccharides. These, in turn, induce expression of xylanase-encoding genes. Here, we aimed to determine which xylan degradation products acted as inducers, and whether the size of the released oligomer correlated with its induction strength. To this end, we compared xylanase production by different inducers, such as sophorose, lactose, cellooligosaccharides, and xylooligosaccharides in Fusarium oxysporum f. sp. lycopersici. Results indicate that xylooligosaccharides are more effective than other substrates at inducing endoxylanase and β-xylosidases. Moreover, we report a correlation between the degree of xylooligosaccharide polymerization and induction efficiency of each enzyme. Specifically, xylotetraose is the best inducer of endoxylanase, xylohexaose of extracellular β-xylosidase, and xylobiose of cell-bound β-xylosidase.

Proteomic analysis reflects an environmental alkalinization-coupled pH-dependent mechanism of regulating lignocellulases in Trichoderma guizhouense NJAU4742

BACKGROUND

Filamentous fungi have the ability to efficiently decompose plant biomass, and thus are widely used in the biofuel and bioprocess industries. In process, ambient pH has been reported to strongly affect the performance of the applied functional filamentous fungi. In this study, Trichoderma guizhouense NJAU4742 was investigated under the fermentation of rice straw at different initial pH values for a detailed study.

RESULTS

The results showed that NJAU4742 strain could tolerate ambient pH values ranging from 3.0 to 9.0, but had significantly higher growth speed and extracellular enzyme activities under acidic conditions. At low ambient pH (< 4), NJAU4742 strain achieved rapid degradation of rice straw by elevating the ambient pH to an optimal range through environmental alkalinization. Further proteomic analysis identified a total of 1139 intracellular and extracellular proteins during the solid-state fermentation processes, including the quantified 190 carbohydrate-active enzymes (CAZymes) responsible for rice straw degradation, such as 19 cellulases, 47 hemicellulases and 11 chitinases. Meanwhile, the analysis results clearly showed that the secreted lignocellulases had a synergistic trend in distribution according to the ambient pH, and thus led to a pH-dependent classification of lignocellulases in T. guizhouense NJAU4742.

CONCLUSIONS

Most functional lignocellulases were found to be differently regulated by the ambient pH in T. guizhouense NJAU4742, which had the ability of speeding up biomass degradation by elevating the ambient pH through environmental alkalinization. These findings contribute to the theoretical basis for the biodegradation of plant biomass by filamentous fungi in the biofuel and bioprocess industries.

Development of novel economical methodologies for zymographic analysis of purified xylano-pectinolytic enzymes using agrowaste-based substrates

In this study, zymographic analysis for xylanase and pectinase enzymes has been carried out using agrowaste residues, wheat bran and citrus peel as well as their extracts. Isozymic forms of xylanase as well as pectinase enzyme displayed comparable zymographic bands onto agar petriplates containing either commercial substrates (xylan and pectin), agrowaste-based substrates (wheat bran and citrus peel), or polysaccharides extracted from these agrowastes (crude xylan and pectin extracted from wheat bran and citrus peel, respectively), indicating the fact that agro residues and their extracts can be utilized as a substitute of cost-intensive commercial substrates, xylan and pectin for zymographic analysis. This is the first report revealing the zymographic analysis of xylano-pectinolytic enzymes using agro-based solid residues particles or polysaccharides extracted from agro-based residues.

Lytic Polysaccharide Monooxygenase from Aspergillus fumigatus can Improve Enzymatic Cocktail Activity During Sugarcane Bagasse Hydrolysis

Background:

Lytic Polysaccharide Monooxygenases (LPMOs) are auxiliary accessory enzymes that act synergistically with cellulases and which are increasingly being used in secondgeneration bioethanol production from biomasses. Several LPMOs have been identified in various filamentous fungi, including Aspergillus fumigatus. However, many LPMOs have not been characterized yet.

Objective:

To report the role of uncharacterized A. fumigatus AfAA9_B LPMO.

Methods:

qRT-PCR analysis was employed to analyze the LPMO gene expression profile in different carbon sources. The gene encoding an AfAA9_B (Afu4g07850) was cloned into the vector pET- 28a(+), expressed in the E. coli strain RosettaTM (DE3) pLysS, and purified by a Ni2+-nitrilotriacetic (Ni-NTA) agarose resin. To evaluate the specific LPMO activity, the purified protein peroxidase activity was assessed. The auxiliary LPMO activity was investigated by the synergistic activity in Celluclast 1.5L enzymatic cocktail.

Results:

LPMO was highly induced in complex biomass like sugarcane bagasse (SEB), Avicel® PH-101, and CM-cellulose. The LPMO gene encoded a protein comprising 250 amino acids, without a CBM domain. After protein purification, the AfAA9_B molecular mass estimated by SDSPAGE was 35 kDa. The purified protein specific peroxidase activity was 8.33 ± 1.9 U g-1. Upon addition to Celluclast 1.5L, Avicel® PH-101 and SEB hydrolysis increased by 18% and 22%, respectively.

Conclusion:

A. fumigatus LPMO is a promising candidate to enhance the currently available enzymatic cocktail and can therefore be used in second-generation ethanol production.

Enhanced reducing sugar production by saccharification of lignocellulosic biomass, Pennisetum species through cellulase from a newly isolated Aspergillus fumigatus

A cellulose degrading fungus Aspergillus fumigatus (CWSF-7) isolated from decomposed lignocellulosic waste containing soil was found to produce high titer of cellulases. The optimum activity of CMCase and FPase were 1.9 U/mL and 0.9 U/mL respectively while the highest protein concentration was found to be 1.2 mg/mL. Saccharification of two Pennisetum grass varieties [dennanath (DG) and hybrid napier grass (HNG)] were optimized using partially purified CMCase and FPase in equal concentration, i.e. a ratios of 1:1 and further with addition of commercial xylanase using response surface methodology (RSM). The production of total reducing sugar (TRS) using isolated cellulase were 396.6 and 355.8 (mg/g), whereas further addition of xylanase had higher TRS titers of 478.7 and 483.3 (mg/g) for DG and HNG respectively as evident from HPLC analysis. Further, characterization of the enzyme saccharified DG and HNG by SEM and ATR-FTIR revealed efficient hydrolysis of cellulose and partially hydrolysis of hemicellulose.

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

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

Xylanase production from marine derived Trichoderma pleuroticola 08ÇK001 strain isolated from Mediterranean coastal sediments

Xylanases constitutes one the most important enzymes with diverse applications in different industries such as bioethanol production, animal feedstock production, production of xylo-oligosaccharides, baking industry, paper and pulp industry, xylitol production, fruit juice, and beer finishing, degumming, and agriculture. Currently, industrial xylanases are mainly produced by Aspergillus and Trichoderma members. Since the marine environments are less studied compared to terrestrial environments and harbors great microbial diversity we aimed to investigate the xylanase production of 88 marine-derived filamentous fungal strains. These strains are semi-quantitatively screened for their extracellular xylanase production and Trichoderma pleuroticola 08ÇK001 xylanase activity was further characterized. Optimum pH and temperature was determined as 5.0 and 50 °C, respectively. The enzyme preparation retained 53% of its activity at pH 5.0 after 1 h and have found resistant against several ions and compounds such as K⁺ , Ba²⁺ , Na⁺ , β-mercaptoethanol, Triton X-100 and toluene. This study demonstrates that marine-derived fungal strains are prolific sources for xylanase production and presents the first report about the production and characterization of xylanase from a marine derived T. pleuroticola strain. The characteristics of T. pleuroticola 08ÇK001 xylanase activity indicate possible employment in some industrial processes such as animal feed, juice and wine industries or paper pulping applications.

Genetics, Molecular, and Proteomics Advances in Filamentous Fungi

Filamentous fungi play a dynamic role in health and the environment. In addition, their unique and complex hyphal structures are involved in their morphogenesis, integrity, synthesis, and degradation, according to environmental and physiological conditions and resource availability. However, in biotechnology, it has a great value in the production of enzymes, pharmaceuticals, and food ingredients. The beginning of nomenclature of overall fungi started in early 1990 after which the categorization, interior and exterior mechanism, function, molecular and genetics study took pace. This mini-review has emphasized some of the important aspects of filamentous fungi, their pattern of life cycle, history, and development of different strategic methods applied to exploit this unique organism. New trends and concepts that have been applied to overcome obstacle because of their basic structure related to genomics and systems biology has been presented. Furthermore, the future aspects and challenges that need to be deciphered to get a bigger and better picture of filamentous fungi have been discussed.

Two degradation strategies for overcoming the recalcitrance of natural lignocellulosic xylan by polysaccharides-binding GH10 and GH11 xylanases of filamentous fungi

The recalcitrance of lignocellulose forms a strong barrier for the bioconversion of lignocellulosic biomass in chemical or biofuel industries. Filamentous fungi are major plant biomass decomposer, and capable of forming all the required enzymes. Here, they characterized the GH10 and GH11 endo-xylanases and a CE1 acetyl-xylan esterase (Axe1) from a superior biomass-degrading strain, Aspergillus fumigatus Z5, and examined how they interact in xylan degradation. Cellulose-binding (CBM1) domain inhibited GH10 xylanase activities for pure xylan, but afforded them an ability to hydrolyze washed corncob particles (WCCP). CBM1-containing GH10 xylanases also showed synergism with CBM1-containing Axe1 in WCCP hydrolysis, and this synergy was strictly dependent on the presence of their CBM1 domains. In contrast, GH11 xylanases had no CBM1, but still could bind xylan and hydrolyzed WCCP; however, no synergism displayed with Axe1. GH10 xylanases and GH11 xylanases showed a pronounced synergism in WCCP hydrolysis, which was dependent on the presence of the CBM1 in GH10 xylanases and absence from GH11 xylanases. They exhibit different mechanisms to bind to cellulose and xylan, and act in synergy when these two structures are intact. These findings will be helpful for the further development of highly efficient enzyme mixtures for lignocellulosic biomass conversion.

Purification, characterization, gene cloning and expression of GH-10 xylanase (Penicillium citrinum isolate HZN13)

An extracellular thermostable xylanase (Xyl-IIb) produced by Penicillium citrinum isolate HZN13 was purified to homogeneity using DEAE-Sepharose, Sephadex G-100 and Bio-Gel P-60 chromatography with specific activity of 6272.7 U/mg and 19.6-fold purification. The purification revealed the occurrence of multiple forms of xylanases (Xyl-I, Xyl-IIa, Xyl-IIb and Xyl-III). The molecular mass of highly purified Xyl-IIb was ~31 kDa with SDS-PAGE. The enzyme was cellulase-free, thermostable (55–75 °C) and acidophilic (3.5–5.0). It was activated by Ca²⁺, Ba²⁺, DTT and β-mercaptoethanol, whereas inhibited by Hg²⁺, Pb²⁺, Ni²⁺ and p-CMB. Purified Xyl-IIb exhibited highest specificity toward birchwood and oat spelts xylan. Kinetics of Xyl-IIb revealed a K_m of 10 mg/ml and 16.7 mg/ml and V_max of 9523g and 15,873 U/mg with birchwood and oat spelts xylan, respectively, indicating high affinity toward birchwood xylan. The xylanase (Xyl-IIb) belongs to glycosyl hydrolase (GH) family 10 based on conserved regions. Xylanase-encoding gene (xynB) consists of 1501 bp with an open reading frame of 264 bp which was predicted to encode a protein having 87 amino acids and shared homology with endo-1,4-beta-xylanase (xynB) gene from Penicillium citrinum. Cloned xynB gene was expressed in E. coli BL21 (DE3) with xylanase activity (80 U/mg) and confirmed to be GH-10 Xyl-IIa based on molecular mass (~40 kDa). These properties of xylanase make it promising for their applications in biofuel industries.