Cloning, Overexpression, and Characterization of a Highly Active Endoinulinase Gene from Aspergillus fumigatus Cl1 for Production of Inulo-Oligosaccharides

Insights in inulin binding and inulin oligosaccharide formation by novel multi domain endo-inulinases from Botrytis cinerea

World-wide, pathogenic fungi such as Botrytis cinerea cause tremendous yield losses in terms of food production and post-harvest food decay. Many fungi produce inulin-type oligosaccharides (IOSs) from inulin through endo-inulinases which typically show a two domain structure. B.cinerea lacks a two domain endo-inulinase but contains a three domain structure instead. Genome mining revealed three and four domain (d4) enzymes in the fungal kingdom. Here, three and two domain enzymes were compared in their capacity to produce IOSs from inulin. Hill kinetics were observed in three domain enzymes as compared to Michaelis-Menten kinetics in two domain enzymes, suggesting that the N-terminal extension functions as a carbohydrate binding module. Analysis of the IOS product profiles generated from purified GF6, GF12, GF16 and GF18 inulins and extensive sugar docking approaches led to enhanced insights in the active site functioning, revealing subtle differences between the endo-inulinases from Aspergillus niger and B. cinerea. Improved insights in structure-function relationships in fungal endo-inulinases offer opportunities to develop superior enzymes for the production of specific IOS formulations to improve plant and animal health (priming agents, prebiotics).

Recent trends in the biotechnology of functional non-digestible oligosaccharides with prebiotic potential

Prebiotics as a part of dietary nutrition can play a crucial role in structuring the composition and metabolic function of intestinal microbiota and can thus help in managing a clinical scenario by preventing diseases and/or improving health. Among the different prebiotics, non-digestible carbohydrates are molecules that selectively enrich a typical class of bacteria with probiotic potential. This review summarizes the current knowledge about the different aspects of prebiotics, such as its production, characterization and purification by various techniques, and its link to novel product development at an industrial scale for wide-scale use in diverse range of health management applications. Furthermore, the path to effective valorization of agricultural residues in prebiotic production has been elucidated. This review also discusses the recent developments in application of genomic tools in the area of prebiotics for providing new insights into the taxonomic characterization of gut microorganisms, and exploring their functional metabolic pathways for enzyme synthesis. However, the information regarding the cumulative effect of prebiotics with beneficial bacteria, their colonization and its direct influence through altered metabolic profile is still getting established. The future of this area lies in the designing of clinical condition specific functional foods taking into consideration the host genotypes, thus facilitating the creation of balanced and required metabolome and enabling to maintain the healthy status of the host.

Efficient production of inulo-oligosaccharides from inulin by exo- and endo-inulinase co-immobilized onto a self-assembling protein scaffold

Inulin can be hydrolyzed by inulinases to yield inulo-oligosaccharides (IOSs), which have great application potential in the food and nutraceutical industries. However, conventional enzymatic production of IOSs is limited by long hydrolysis times and poor thermo-stability of inulinases. Here, the self-assembling protein scaffold EutM was engineered to co-immobilize exo-inulinase (EXINU) and endo-inulinase (ENINU) for synergistic hydrolysis of inulin to produce IOSs with 3 to 5 monosaccharide units (DP3-5 IOSs). The immobilization of EXINU/ENINU onto the EutM scaffold resulted in an increase of catalytic efficiency, a 65% increase of the V_max of ENINU, as well as an increase of thermo-stability, with 4.26-fold higher residual activity of EXINU after 22 h-incubation at 50 °C. After optimization, two efficient production protocols were obtained, in which the yield and productivity of DP3-5 IOSs reached 80.38% and 70.86 g·(L·h)^-1, respectively, which were at a high level in similar studies. Overall, this study provides an attractive self-assembling protein platform for the co-immobilization of inulinases, as well as optimized bioprocesses with great promise for the industrial production of DP3-5 IOSs.

Bioprocess Optimisation for High Cell Density Endoinulinase Production from Recombinant Aspergillus niger

Endoinulinase gene was expressed in recombinant Aspergillus niger for selective and high-level expression using an exponential fed-batch fermentation. The effects of the growth rate (μ), glucose feed concentration, nitrogen concentration and fungal morphology on enzyme production were evaluated. A recombinant endoinulinase with a molecular weight of 66 kDa was secreted. Endoinulinase production was growth associated at μ> 0.04 h-1, which is characteristic of the constitutive gpd promoter used for the enzyme production. The highest volumetric activity (670 U/ml) was achieved at a growth rate of 93% of μmax (0.07 h-1), while enzyme activity (506 U/ml) and biomass substrate yield (0.043 gbiomassDW/gglucose) significantly decreased at low μ (0.04 h-1). Increasing the feed concentration resulted in high biomass concentrations and viscosity, which necessitated high agitation to enhance the mixing efficiency and oxygen. However, the high agitation and low DO levels (ca. 8% of saturation) led to pellet disruption and growth in dispersed morphology. Enzyme production profiles, product (Yp/s) and biomass (Yx/s) yield coefficients were not affected by feed concentration and morphological change. The gradual increase in the concentration of nitrogen sources showed that, a nitrogen limited culture was not suitable for endoinulinase production in recombinant A. niger. Moreover, the increase in enzyme volumetric activity was still directly related to an increase in biomass concentration. An increase in nitrogen concentration, from 3.8 to 12 g/L, resulted in volumetric activity increase from 393 to 670 U/ml, but the Yp/s (10053 U/gglucose) and Yx/s (0.049 gbiomasDWs/gglucose) did not significantly change. The data demonstrated the potential of recombinant A. niger and high cell density fermentation for the development of large-scale endoinulinase production system.

Exo-inulinase production from Aspergillus fumigatus NFCCI 2426: purification, characterization, and immobilization for continuous fructose production

Aspergillus fumigatus was found to produce thermostable exo-inulinase (EC 3.8.1.80; 38 U/ml) on inulin-rich infusions. Exo-inulinase (14.6 U/mg) was immobilized on glutaraldehyde activated Ca-alginate beads for continuous generation of fructose by hydrolyzing sucrose, chicory, and dandelion substrates. Immobilization of enzyme was confirmed by microscopic and spectroscopic techniques. The exo-inulinase was purified using ion-exchange (1.30-folds) and size-exclusion chromatography (2.71-folds). The purified exo-inulinase showed 64 kDa band on gel and was optimally active at 60 °C and pH 6.0. Kinetic constants, Km and Vmax of purified exo-inulinase, were 5.88 mM and 1.66 µM/min, respectively, and its relative activity was found to be enhanced (125.8%) in the presence of calcium ion. Immobilized preparation was utilized for continuous generation of fructose from chicory juice (26 to 70%) and dandelion root extracts (16 to 24%) by recycling upto five cycles, respectively. In comparison to other sweeteners, such as sucrose, fructose is considered as a healthy alternative. The present study demonstrated the use of immobilized exo-inulinase in continuous generation of fructose from some underutilized plant sources that can be used in food industry. PRACTICAL APPLICATION: Thermostable exo-inulinase produced by A. fumigatus was immobilized on calcium alginate matrix and was employed for continuous hydrolysis of chicory juice and dandelion root extract for generation of fructose syrup.

Understanding the interactive influence of hydrolytic conditions on biocatalytic production of fructooligosaccharides from inulin

Statistical optimization of hydrolytic conditions for the production of fructooligosaccharides (FOSs) from pure inulin using Aspergillus tritici endoinulinase was carried out in a batch system. FOSs yield 99.19% was obtained under the optimized hydrolytic conditions i.e. inulin concentration (7.3%), enzyme load (65 IU), hydrolysis time (13 h) and agitation (100 rpm). The closeness of value of co-efficient of determination (R²) to 1, good agreement between model's predicted and experimental values, low percentage error (<5%), high adequate precision (>4%) and F value (11,634.32), and low Lack of fit (0.60) of the designed model authenticates its fitness. High substrate concentration, low enzyme load and short hydrolysis span justifies efficiency of developed process for the preparation of FOSs from inulin using fungal endoinulinase. TLC chromatographic and densitometry studies confirmed the synthesis of short-chain length FOSs. FOSs preparation contained 33.85% GF2 (ketose), 24.50% GF3 (nystose), 7.26% GF4 (fructofuranosylnystose) and 33.58% FOSs of DP5-9.

Investigating the effect of different inulin-rich substrate preparations from Jerusalem artichoke (Helianthus tuberosus L.) tubers on efficient inulooligosaccharides production

Commercial production of inulooligosaccharides (IOS) relies largely on chicory roots. However, Jerusalem artichoke (JA) tubers provide a suitable alternative due to their high inulin content and low cultivation requirements. In this study, three inulin-rich substrate preparations from JA were investigated to maximize IOS production, namely powder from dried JA tuber slices (Substrate 1), solid residues after extracting protein from the JA powder (Substrate 2) and an inulin-rich fraction extracted from protein extraction residues (Substrate 3). The preferred temperature, pH and inulin substrate concentration were determined after which enzyme dosage and extraction time were optimized to maximize IOS extraction from the three substrates, using pure chicory inulin as benchmark. Under the optimal conditions, Substrate 3 resulted in the highest IOS yield of 82.3% (w/w_inulin). However, IOS production from the Substrate 1 proved more efficient since it renders the highest overall IOS yield (mass of IOS per mass of the starting biomass). In the case of co-production of protein and IOS from the JA tuber in a biorefinery concept, IOS production from the Substrate 2 is preferred since it reduces the inulin losses incurred during substrate preparation. For all the inulin-rich substrates studied, an enzyme dosage of 14.8 U/g_inulin was found to be optimal at reaction time less than 6 h. JA tuber exhibited excellent potential for commercial production of IOS with improved yield and the possible advantage of a reduced biomass cost.

Physiochemical, kinetic and thermodynamic studies on Aspergillus wewitschiae MN056175 inulinase with extraction of prebiotic and antioxidant Cynara scolymus leaves fructo-oligosaccharides

Utilization of agricultural wastes as cheap natural resources for production of bioactive products is currently attracting global attention. For this purpose, this study focused on isolation of Aspergillus wewitschiae MN056175 as promising producer of inulinase, then investigating physiochemical, kinetics and thermodynamics of the obtained inulinase, and its ability to extract bioactive fructo-oligosaccharides (FOS) from Cynara scolymus leaves (artichoke leaves, AL). A. wewitschiae MN056175 inulinase gave the maximum activity at temperature 60 °C and inulin concentration 1%. The kinetics including K_m and V_max were determined to be 105.26 mg·ml^-1 and 83.33 μmol·ml^-1·min^-1, respectively. The thermodynamics including, E_a (activation energy) and E_d (activation energy for denaturation) were determined to be 21.82 and 73.21 kJ·mol^-1, K_d, T_1/2, D-value, ΔH°, ΔG° and ΔS° at 40, 50 and 60 °C which indicated the stability of A. wewitschiae MN056175 inulinase. Moreover, this inulinase was capable of hydrolyzing Cynara scolymus leaves into reducing sugar and 15 FOS with different DP, total carbohydrate, and protein content under different conditions designed by central composite design (CCD). The 15 AL FOS showed different high antioxidant and prebiotic activities. Central FOS with probiotic bacteria exhibited significant antimicrobial activity against tested gram positive bacteria in a way higher than those recorded against gram negative bacteria.

Production of Short Chain Fructo-oligosaccharides from Inulin of Chicory Root Using Fungal Endoinulinase

Short chain fructo-oligosaccharides (SC-FOS) are the potential prebiotics possessing diverse applications in both food and feed industries. The present study was aimed to extract inulin from chicory roots followed by its conversion into SC-FOS applying endoinulinase from Aspergillus fumigatus. The inulin was extracted from chicory roots through boiling in hot water, followed by precipitation with ethanol at room temperature or freezing condition. Maximum yield (42%) of inulin was obtained with three volumes of chilled absolute ethanol at room temperature. HPLC analysis of enzymatic hydrolysate detected kestose (GF2), nystose (GF3), and other FOS having higher degree of polymerization (DP). Maximum GF2 (5.79 mg/ml) was detected at temperature 50 °C, pH 5.5 with 2 U of enzyme dose after 6 h of hydrolysis; while maximum GF3 (4.33 mg/ml) was recorded at 60 °C, 5.5 pH with 0.5 U enzyme dose after 2 h of hydrolysis. Nevertheless, complete hydrolysis of inulin was noticed with 99% total oligosaccharide yield at 55 °C, 5.5 pH with 0.5 U enzyme dose after 4 h of hydrolysis with negligible amount of mono- and di-saccharides. The present finding demonstrated the process for higher yield of inulin from chicory roots followed by its conversion into SC-FOS applying fungal endoinulinase.

A new engineered endo-inulinase with improved activity and thermostability: Application in the production of prebiotic fructo-oligosaccharides from inulin

To construct a high-performance engineered endo-inulinase for fructo-oligosaccharides (FOS) production from inulin, an inulin binding module (IBM) was fused into either N- or C-terminal of an endo-inulinase. After heterologous expression, purification and characterization, the C-terminal fusion one (Eninu-IBM) with better activity, thermostability and inulin binding ability was employed for high-temperature in situ inulin hydrolysis in a 10-L fermentor. During this process, Eninu-IBM was first efficiently produced by the yeast cells at 28 °C for 96 h, and subsequently 1600 g unsterilized inulin per liter fermentation liquor was directly supplemented into the bioreactor for FOS production at 60 °C for 2 h. Finally, high purity of FOS (91.4%) were obtained with FOS titer, yield and productivity of 717.3 g/L, 0.912 g_FOS/g_Inulin and 358.6 g/L/h, respectively. The in vitro prebiotic assay indicated that the final FOS products with main polymerization degrees of 3-5 were preferably fermented by beneficial bifidobacteria and lactobacilli.

High level production of a recombinant acid stable exoinulinase from Aspergillus kawachii

Exoinulinases-enzymes extensively studied in recent decades because of their industrial applications-need to be produced in suitable quantities in order to meet production demands. We describe here the production of an acid-stable recombinant inulinase from Aspergillus kawachii in the Pichia pastoris system and the recombinant enzyme's biochemical characteristics and potential application to industrial processes. After an appropriate cloning strategy, this genetically engineered inulinase was successfully overproduced in fed-batch fermentations, reaching up to 840 U/ml after a 72-h cultivation. The protein, purified to homogeneity by chromatographic techniques, was obtained at a 42% yield. The following biochemical characteristics were determined: the enzyme had an optimal pH of 3, was stable for at least 3 h at 55 °C, and was inhibited in catalytic activity almost completely by Hg⁺². The respective K_m and V_max for the recombinant inulinase with inulin as substrate were 1.35 mM and 2673 μmol/min/mg. The recombinant enzyme is an exoinulinase but also possesses synthetic activity (i. e., fructosyl transferase). The high level of production of this recombinant plus its relevant biochemical properties would argue that the process presented here is a possible recourse for industrial applications in carbohydrate processing.

Efficient Secretory Overexpression of Endoinulinase in Escherichia coli and the Production of Inulooligosaccharides

Endoinulinase production was achieved by heteroexpression of endoinulinase-encoding gene from Aspergillus ficuum which is an eukaryotic organism in Escherichia coli BL21 (DE3). Further analysis demonstrated that the native signal peptide existed in inu2 gene lowered the enzyme expression level. To realize extracellular accumulation of target protein and improve its expression level, native signal peptide was substituted with pelB, ompC, and pelB fusing with the native signal peptides; then, the effects on endoinulinase production were investigated. As a result, E. coli A606-3, with replacement of pelB as its signal peptide, showed the highest endoinulinase enzyme activity (75.22 U/mg). Also, it suggested that eukaryotic signal peptides have an inhibition on enzyme expression in prokaryotic organism. Moreover, the condition for inulooligosaccharide (IOS) production from inulin was optimized, and an IOS yield of 94.41 % was achieved under the condition of 15 % (w/v) inulin, purified endoinulinase dosage of 5 U/g inulin, 55 °C, and pH 4.6 for 24 h. The major products of hydrolysis of inulin were identified as DP3 to DP7.