Properties of an extracellular glycosidase of Aspergillus niger suitable for removal of oligosaccharides from cowpea meal

Microbial production and biotechnological applications of α-galactosidase

α-Galactosidase, (E.C. 3.2.1.22) is an exoglycosidase that target galactooligosaccharides such as raffinose, melibiose, stachyose and branched polysaccharides like galactomannans and galacto-glucomannans by catalysing the hydrolysis of α-1,6 linked terminal galactose residues. The enzyme has been isolated and characterized from microbial, plant and animal sources. This ubiquitous enzyme possesses physiological significance and immense industrial potential. Optimization of the growth conditions and efficient purification strategies can lead to a significant increase in the enzyme production. To boost commercial productivity, cloning of novel α-galactosidase genes and their heterologous expression in suitable host has gained popularity. Enzyme immobilization leads to its greater reutilization, superior thermostability, pH tolerance and increased activity. The enzyme is well explored in food industry in the removal of raffinose family oligosaccharides (RFOs) in soymilk and sugar crystallization process. It also improves animal feed quality and biomass processing. Applications of the enzyme is in the area of biomedicine includes therapeutic advances in treatment of Fabry disease, blood group conversion and removal of α-gal type immunogenic epitopes in xenotransplantation. With considerable biotechnological applications, this enzyme has been vastly commercialized and holds greater future prospects.

Mapping the polysaccharide degradation potential of Aspergillus niger

Background

The degradation of plant materials by enzymes is an industry of increasing importance. For sustainable production of second generation biofuels and other products of industrial biotechnology, efficient degradation of non-edible plant polysaccharides such as hemicellulose is required. For each type of hemicellulose, a complex mixture of enzymes is required for complete conversion to fermentable monosaccharides. In plant-biomass degrading fungi, these enzymes are regulated and released by complex regulatory structures. In this study, we present a methodology for evaluating the potential of a given fungus for polysaccharide degradation.

Results

Through the compilation of information from 203 articles, we have systematized knowledge on the structure and degradation of 16 major types of plant polysaccharides to form a graphical overview. As a case example, we have combined this with a list of 188 genes coding for carbohydrate-active enzymes from Aspergillus niger, thus forming an analysis framework, which can be queried. Combination of this information network with gene expression analysis on mono- and polysaccharide substrates has allowed elucidation of concerted gene expression from this organism. One such example is the identification of a full set of extracellular polysaccharide-acting genes for the degradation of oat spelt xylan.

Conclusions

The mapping of plant polysaccharide structures along with the corresponding enzymatic activities is a powerful framework for expression analysis of carbohydrate-active enzymes. Applying this network-based approach, we provide the first genome-scale characterization of all genes coding for carbohydrate-active enzymes identified in A. niger.

Effect of cultivating conditions on alpha-galactosidase production by a novel Aspergillus foetidus ZU-G1 strain in solid-state fermentation

The work is intended to achieve optimum culture conditions of alpha-galactosidase production by a mutant strain Aspergillus foetidus ZU-G1 in solid-state fermentation (SSF). Certain fermentation parameters involving moisture content, incubation temperature, cultivation period of seed, inoculum volume, initial pH value, layers of pledget, load size of medium and period of cultivation were investigated separately. The optimal cultivating conditions of alpha-galactosidase production in SSF were 60% initial moisture of medium, 28 degrees C incubation temperature, 18 h cultivation period of seed, 10% inoculum volume, 5.0 approximately 6.0 initial pH of medium, 6 layers of pledget and 10 g dry matter loadage. Under the optimized cultivation conditions, the maximum alpha-galactosidase production was 2 037.51 U/g dry matter near the 144th hour of fermentation.

Optimization of the fermentation medium for alpha-galactosidase production from Aspergillus foetidus ZU-G1 using response surface methodology

The optimization of fermentation medium for alpha-galactosidase production by Aspergillus foetidus ZU-G1 was investigated in shaker flask fermentation. A one-factor-at-a-time experiment was used to screen the preferable nutriment (carbon sources, nitrogen sources, and essential elements) for alpha-galactosidase production. A fractional factorial design was used to screen the main 5 factors, soybean meal, wheat bran, KH2PO4, FeSO4 x 7 H2O, and the medium initial pH, that affected the production of alpha-galactosidase. The central composite experimental design was further adopted to derive a statistical model for optimizing the composition of the fermentation medium. The experimental results showed that the optimum fermentation medium for alpha-galactosidase production by Aspergillus foetidus ZU-G1 was composed of 3.2% soybean meal (w/v), 2% wheat bran (w/v), 0.1% KH2PO4 (w/v), and 0.05% FeSO4 x 7 H2O (w/v); initial medium pH was 6.31. The results further predicted that alpha-galactosidase activity reached 64.75 U/mL after 96-h incubation in this medium, which was approximately 7 times higher than that incubated in the nonoptimized medium. The time course of alpha-galactosidase production in the optimized medium composition was also carried out to validate the model.

Processing of soybean products by semipurified plant and microbial alpha-galactosidases

Galactooligosaccharides (GO) are responsible for intestinal disturbances following ingestion of legume-derived products. Enzymatic reduction of GO level in these products is highly desirable to improve their acceptance. For this purpose, plant and microbial semipurified alpha-galactosidases were used for GO hydrolysis in soybean flour and soy molasses. alpha-Galactosidases from soybean germinating seeds, Aspergillus terreus, and Penicillium griseoroseum presented maximal activities at pH 4.0-5.0 and 45-65 degrees C. The KM,app values determined for raffinose by the soybean, A. terreus, and P. griseoroseum alpha-galactosidases were 3.44, 19.39, and 20.67 mM, respectively. The enzymes were completely inhibited by Ag+ and Hg2+, whereas only soybean enzyme was inhibited by galactose. A. terreus alpha-galactosidase was more thermostable than the enzymes from the other two sources. This enzyme maintained about 100% of its original activity after 3 h at 60 C. The microbial alpha-galactosidases were more efficient for reducing GO in soybean flour and soy molasses than soybean enzyme.

Enzymatic degradation of oligosaccharides in pinto bean flour

The use of dry edible beans is limited due to the presence of flatulence factors, the raffinose oligosaccharides. Our objective was to investigate the process for the removal of oligosaccharides from pinto bean using enzymatic treatment and to compare it to removal by soaking and cooking methods. Crude enzyme preparation was produced by six fungal species on wheat bran- and okara-based substrates with soy tofu whey. The loss of raffinose oligosaccharides after soaking pinto beans for 16 h at the room temperature was 10%, after cooking for 90 min was 52%, and after autoclaving for 30 min was 58%. On the other hand, the treatment using crude alpha-galactosidase (60 U mL(-1)) produced by Aspergillus awamori NRRL 4869 from wheat bran-based substrate with soy tofu whey on pinto bean flour for 2 h completely hydrolyzed raffinose oligosaccharides. These results supported that the enzymatic treatment was the most effective among various processing methods tested for removing the raffinose oligosaccharides, and hence, crude alpha-galactosidases from fungi have potential use in the food industry.

Aspergillus enzymes involved in degradation of plant cell wall polysaccharides

Degradation of plant cell wall polysaccharides is of major importance in the food and feed, beverage, textile, and paper and pulp industries, as well as in several other industrial production processes. Enzymatic degradation of these polymers has received attention for many years and is becoming a more and more attractive alternative to chemical and mechanical processes. Over the past 15 years, much progress has been made in elucidating the structural characteristics of these polysaccharides and in characterizing the enzymes involved in their degradation and the genes of biotechnologically relevant microorganisms encoding these enzymes. The members of the fungal genus Aspergillus are commonly used for the production of polysaccharide-degrading enzymes. This genus produces a wide spectrum of cell wall-degrading enzymes, allowing not only complete degradation of the polysaccharides but also tailored modifications by using specific enzymes purified from these fungi. This review summarizes our current knowledge of the cell wall polysaccharide-degrading enzymes from aspergilli and the genes by which they are encoded.

Differential expression of three alpha-galactosidase genes and a single beta-galactosidase gene from Aspergillus niger

A gene encoding a third alpha-galactosidase (AglB) from Aspergillus niger has been cloned and sequenced. The gene consists of an open reading frame of 1,750 bp containing six introns. The gene encodes a protein of 443 amino acids which contains a eukaryotic signal sequence of 16 amino acids and seven putative N-glycosylation sites. The mature protein has a calculated molecular mass of 48,835 Da and a predicted pI of 4.6. An alignment of the AglB amino acid sequence with those of other alpha-galactosidases revealed that it belongs to a subfamily of alpha-galactosidases that also includes A. niger AglA. A. niger AglC belongs to a different subfamily that consists mainly of prokaryotic alpha-galactosidases. The expression of aglA, aglB, aglC, and lacA, the latter of which encodes an A. niger beta-galactosidase, has been studied by using a number of monomeric, oligomeric, and polymeric compounds as growth substrates. Expression of aglA is only detected on galactose and galactose-containing oligomers and polymers. The aglB gene is expressed on all of the carbon sources tested, including glucose. Elevated expression was observed on xylan, which could be assigned to regulation via XlnR, the xylanolytic transcriptional activator. Expression of aglC was only observed on glucose, fructose, and combinations of glucose with xylose and galactose. High expression of lacA was detected on arabinose, xylose, xylan, and pectin. Similar to aglB, the expression on xylose and xylan can be assigned to regulation via XlnR. All four genes have distinct expression patterns which seem to mirror the natural substrates of the encoded proteins.

Characterization of galactosidases from Aspergillus niger: purification of a novel alpha-galactosidase activity

An enzyme with beta-galactosidase activity and three proteins exhibiting alpha-galactosidase activity were purified from a culture filtrate of Aspergillus niger grown on arabinoxylan. beta-galactosidase, optimally active at pH 4 and 60-65 degrees C, was active against p-nitrophenyl-beta-D-galactopyranoside, lactose, and pectic galactan. It was not able to release galactose from sugar beet pectin or lemon pectin. Its action on pectic galactan was increased by the presence of beta-galactanase. The three forms of alpha-galactosidase activity that showed different molecular masses and pIs were found to have the same mass after deglycosylation with N-glycanase F and to be the same protein based on their N-terminal amino acid sequence data. The purified alpha-galactosidase was shown to be different from alpha-galactosidase A from A. niger. This confirmed the existence of at least two different alpha-galactosidases in A. niger. alpha-Galactosidase, optimally active at pH 4.5 and 50-55 degrees C, was active toward p-nitrophenyl-alpha-D-galactopyranoside, melibiose, raffinose, stachyose, and locust bean gum, on which substrate it exhibited synergism with beta-mannanase.