Microbial 16β-Hydroxylation of Steroids with Aspergillus niger

Microbial 16β-hydroxylation of some steroids with Wojnowicia graminis, Corticium centrifugum and Bacillus megaterium has been reported, but not 16β-hydroxylation of normal 17-oxo steroids with Aspergillus niger. This time, we tried microbial transformation of dehydroepiandrosterone with this fungus, and obtained 4-androstene-3,17-dione, 17β-hydroxy-4-androstene-3,16-dione, 16β,17β-dihydroxy-4-androsten-3-one and a new compound, 16β-hydroxy-4-androstene-3,17-dione. This new compound was also obtained by the fermentation of 4-androstene-3,17-dione and testosterone.     

Microbial transformations of (−)-α- and (+)-β-thujone by fungi of Absidia species

The microbial transformations of (−)-α- and (+)-β-thujone (1a and 1b) in cultures of Absidia species: Absidia coerulea AM93, Absidia glauca AM254 and Absidia cylindrospora AM336 were studied. The biotransformations of (−)-α-thujone (1a), by these fungi strains, afforded mixtures of 4-hydroxy- and 7-hydroxy-α-thujone (2 and 3). Aforementioned fungi strains were also able to hydroxylate of (+)-β-thujone at C-7 position. Only A. glauca AM254 transformed 1b to 8-hydroxy-β-thujone (7) and (2S)-2-hydroxyneoisothujol (6). The (4R)-4-hydroxyisothujole (5) was identified as one of the major metabolite of (+)-β-thujone (1b) in culture of A. cylindrospora AM336. This strain was also able to introduce hydroxy group to C-4 position in 1b without reduction of carbonyl group at C-3. The absolute configuration of all chiral centers of new (4R)-4-hydroxyisothujol (5) and (2S)-2-hydroxyneoisothujol (6) were established taking into account the configuration of (+)-β-thujone (1b) and their spectral data.     

Fed-batch biotransformation of β-ionone by Aspergillus niger

Aspergillus niger IFO 8541 was found to be an efficient biocatalyst for the biotransformation of -ionone into hydroxy and oxo derivatives. The reaction had to be carried out with an inoculum made of about 4 × 10⁷ fresh spores/l and with a preliminary growth period giving at least 3 g/l biomass. The fungus developed in the form of pellets when cultivated as free mycelium; entrapment of the microorganism in calcium alginate beads was an efficient way to mimic this feature in an aerated, stirred bioreactor. The biotransformation was carried out using a fed-batch mode of operation involving sequential precursor addition. -Ionone stopped the fungal growth and was converted into metabolites only when the carbon source remained present in the medium; it was fully oxidized after sucrose exhaustion. These conditions allowed recovery of about 2.5 g/l aroma compounds after 230 h cultivation with a molar yield close to 100%.     

Over-production of β-glucosidase by Aspergillus niger mutant from lignocellulosic biomass

The maximum yield of -glucosidase by A. niger KK2 mutant, grown on the basal medium for 7 days, was 514 I U g^–1 ground rice straw, and was about twice those obtained from wheat straw or bran by previous researchers. Optimal activity of -glucosidase was at 60–70 °C and pH 4.8.     

Synthesis of new oligosaccharides from raffinose by Aspergillus niger fructosyltransferase

Purified fructosyltransferase from Aspergillus niger exhibited transfructosylation activities, producing fructose, DP2, DP4, and DP5 from raffinose. The structures of two products synthesized from raffinose were identified as O--d-galactopyranosyl (16)--d-glucopyranose and O--d-galactopyranosyl (16)--d-glucopyranosyl-[O--d-fructofuranosyl (21)]--D-fructofuranoside, which means that C-2 hydroxyl group of fructose released from one raffinose molecule were linked to the C-1 hydroxyl group of fructose of another raffinose.     

Proteolytic inactivation of 1, 4-α-d-glucan 6-α-d-glucosyltransferase purified from Aspergillus niger R-27

An extracellular 1,4-α-d-glucan 6-α-d-glucosyltransferase [d-glucosyltransferase, 1,4-α-d-glucan:1,4-α-d-glucan(d-gluco 6-α-d-glucosyltransferase, EC 2.4.1.24] from Aspergillus niger R-27 has been purified and the kinetics of its proteolytic inactivation with subtilisin studied. The purified enzyme was shown to be homogeneous using disc polyacrylamide gel electrophoresis. It contained 16.0% mannose, 0.19% glucose and 2.95% 2-acetamido-2-deoxy-d-glucose. The characteristic feature of the proteolytic degradation of glucosyltransferase is rapid hydrolysis of ～12 peptide bonds per mol and the formation of an active intermediate product which is more resistant to further proteolysis, but is easily heat-inactivated. The isolation and some properties of glucosyltransferase are also described.     

Molecular cloning,expression and structure of the endo-1,5-α-l-arabinase gene of Aspergillus niger

Secretion of endo-1,5--l-arabinase A (ABNA) by an Aspergillus niger xylulose kinase mutant upon mycelium transfer to medium containing l-arabitol was immunochemically followed with time to monitor its induction profile. A cDNA expression library was made from polyA ⁺ RNA isolated from the induced mycelium. This library was immunochemically screened and one ABN A specific clone emerged. The corresponding abnA gene was isolated from an A. niger genomic library. Upon Southern blot analysis, a 3.1-kb HindIII fragment was identified and subcloned to result in plasmid pIM950. By means of co-tranformation using the A. niger pyrA gene as selection marker, the gene was introduced in both A. niger and A. nidulans uridine auxotrophic mutants. Prototrophic A. niger and A. nidulans transformants overproduced A. niger ABN A upon growth in medium containing sugar beet pulp as the sole carbon source, thereby establishing the identity and functionality of the cloned gene. The DNA sequence of the complete HindIII fragment was determined and the structure of the abnA gene as well as of its deduced gene product were analysed. Gene abnA contains three introns within its structural region and codes for a protein of 321 amino acids. Signal peptide processing results in a mature protein of 302 amino acids with a deduced molecular mass of 32.5 kDa. A. niger abnA is the first gene encoding an ABN to be isolated and characterized. Correspondence to: L. H. de Graaff     

Glucoamylase and α-amylase production by immobilized Aspergillus niger

Summary Aspergillus niger mycelia or spores were immobilized in calcium alginate gel beads and employed for production of glucoamylase and -amylase by repeated batch process. The immobilized mycelium produced lower enzyme activities than immobilized spores germinated in a growth medium and subsequently cultured in an enzyme production medium. In repeated batch experiments, free cells could be used for only 4 4-day batches, whereas with immobilized spores at least 11 4-day batches with a gradual increase in enzyme activities in each successive batch were possible. The activity ratio of glucoamylase and -amylase produced was altered by immobilization.     

Bimutation breeding of Aspergillus niger strain for enhancing β-mannanase production by solid-state fermentation

A parent strain Aspergillus niger LW-1 was mutated by the compound mutagenesis of vacuum microwave (VMW) and ethyl methane sulfonate (EMS). A mutant strain, designated as A. niger E-30, with high- and stable-yield β-mannanase was obtained through a series of screening. The β-mannanase activity of the mutant strain E-30, cultivated on the basic fermentation medium at 32 °C for 96 h, reached 36,675 U/g dried koji, being 1.98-fold higher than that (18,501 U/g dried koji) of the parent strain LW-1. The purified E-30 β-mannanase, a glycoprotein with a carbohydrate content of 19.6%, had an apparent molecular weight of about 42.0 kDa by SDS–PAGE. Its optimal pH and temperature were 3.5 and 65 °C, respectively. It was highly stable at a pH range of 3.5–7.0 and at a temperature of 60 °C and below. The kinetic parameters K_m and V_max, toward locust bean gum and at pH 4.8 and 50 °C, were 3.68 mg/mL and 1067.5 U/mg, respectively. The β-mannanase activity was not significantly affected by an array of metal ions and EDTA, but strongly inhibited by Ag⁺ and Hg²⁺. In addition, the hydrolytic conditions of konjak glucomannan using the purified E-30 β-mannanase were optimized as follows: konjak gum solution 240 g/L (dissolved in deionized water), hydrolytic temperature 50 °C, β-mannanase dosage 120 U/g konjak gum, and hydrolytic time 8 h.     

Facile production of Aspergillus niger α-N-acetylgalactosaminidase in yeast

α-N-Acetylgalactosaminidase (α-GalNAc-ase; EC.3.2.1.49) is an exoglycosidase specific for the hydrolysis of terminal α-linked N-acetylgalactosamine in various sugar chains. The cDNA corresponding to the α-GalNAc-ase gene was cloned from Aspergillus niger, sequenced, and expressed in the yeast Saccharomyces cerevisiae. The α-GalNAc-ase gene contains an open reading frame which encodes a protein of 487 amino acid residues. The molecular mass of the mature protein deduced from the amino acid sequence of this reading frame is 54 kDa. The recombinant protein was purified to apparent homogeneity and biochemically characterized (pI4.4, K(M) 0.56 mmol/l for 2-nitrophenyl 2-acetamido-2-deoxy-α-d-galactopyranoside, and optimum enzyme activity was achieved at pH2.0-2.4 and 50-55°C). Its molecular weight was determined by analytical ultracentrifuge measurement and dynamic light scattering. Our experiments confirmed that the recombinant α-GalNAc-ase exists as two distinct species (70 and 130 kDa) compared to its native form, which is purely monomeric. N-Glycosylation was confirmed at six of the eight potential N-glycosylation sites in both wild type and recombinant α-GalNAc-ase.     

Detection of endogenous β-glucuronidase activity in Aspergillus niger

 An endogenous β-glucuronidase that hydrolyses the chromogenic substrate 5-bromo-4-chloro-3-indolyl-β-D-glucuronide (X-gluc) in Aspergillus niger is reported. The activity was induced when the fungus was grown in media containing xylan, but was either very low, or absent, when grown on glucose. Endogenous β-glucuronidase was primarily located in newly formed hyphae, and was apparent at pH values between 3 and 6. Hydrolysis of X-gluc was sensitive to the inhibitor D-saccharic acid 1,4-lactone and was irreversibly inactivated by heating. The bacterial uidAβ-glucuronidase reporter gene was strongly expressed in the hyphae of transformed A. niger but, in contrast to the endogenous activity, the enzyme was also active at pH 7–8.5. Histochemical localization of uidA expression in A. niger, without interference from the endogenous β-glucuronidase activity, was achieved by staining at this pH. Received : 22 March 1995/Received last revision : 17 August 1995/Accepted : 22 August 1995     

Transformations of acyclic isoprenoids by Aspergillus niger: selective oxidation of ω-methyl and remote double bonds

A strain of Aspergillus niger was used to study the mode of biotransformation of various acyclic isoprenoids. The organism showed ability to carry out the oxidation of the -methyl and the remote double bond regio-and stereospecifically, resulting in the formation of -methyl hydroxylated and vicinal trans-diols in all the compounds tested (I-VII). However, these two activities seem to have preferential structural requirements. When an acyclic isoprenoid with a ketone functionality such as geranylacetone was used as the substrate, the organism also carried out asymmetric reduction of the keto group. Correspondence to: K. M. Madyastha     

Highly selective biotransformation of (+)-(1S)- and (−)-(1R)-camphorquinone by Aspergillus wentii

Abstract

To clarify the structures of biotransformation products and metabolic pathways, the biotransformation of monoterpenoids, (+)- and (?)-camphorquinone (1a and b), has been investigated using Aspergillus wentii as a biocatalyst. Compound 1a was converted to (?)-(2S)-exo-hydroxycamphor (2a), (?)-(2S)-endo-hydroxycamphor (3a), (?)-(3S)-exo-hydroxycamphor (4a), (?)-(3S)-endo-hydroxycamphor (5a), and (+)-camphoric acid (6a). Compound 1b was converted to (+)-(2R)-exo-hydroxycamphor (2b), (+)-(2R)-endo-hydroxycamphor (3b), (+)-(3R)-exo-hydroxycamphor (4b), (+)-(3R)-endo-hydroxycamphor (5b), and (?)-camphoric acid (6b). Compound 1a mainly produced 2a (65.0%) with stereoselectivity, whereas 1b afforded 3b (84.3%) with high stereoselectivity. These structures were confirmed by gas chromatography–mass spectrometry, infrared, ¹H nuclear magnetic resonance (NMR), and ¹³C NMR spectral data. The products illustrate the marked ability of A. wentii for enzymatic oxidation and ketone reduction.     

Cloning of the Aspergillus niger gene encoding α-l-arabinofuranosidase A

Using l-arabitol as an inducer, simple induction conditions were established that resulted in high-level expression of -l-arabinofuranosidase A by an Aspergillus niger d-xylulose kinase mutant strain. These conditions were adapted to construct a cDNA expression library from which an -l-arabinofuranosidase A cDNA clone was isolated using specific antiserum. The corresponding gene encoding -l-arabinpfuranosidase A (abfA) was isolated from a genomic library and cloned into a high copy plasmid vector. By co-transformation of uridine auxotrophic mutants lacking orotidine-5-phosphate decarboxylase activity, the afbA gene was introduced both in A. niger and A. nidulans, using the A. niger pyrA gene as selection marker. The identity of the abfA gene was confirmed by overexpression of the gene product by A. niger and A. nidulans transformants, upon growth using sugar beet pulp as the carbon source.     

Formation of β-Fructosyl Compounds of Pyridoxine in Growing Culture of Aspergillus niger

Two pyridoxine compounds were found to be formed in a culture filtrate of Aspergillus niger and A. sydowi, when grown in a medium containing sucrose and pyridoxine. Each of the two compounds I and II was obtained as a white powdered preparation by preparative paper chromatography, gel filtration on Toyopearl HW-40S and Sephadex G-10 columns, DEAE-cellulose column chromatography, and lyophilization. Compounds I and II were identified as 5?-O-(β-D-fructofuranosyl)-pyridoxine and 5?-O-(β-D-fructofuranosyl-(2→1)-β-D-fructofuranosyl]-pyridoxine, on the basis of the various experimental results, viz., elementary analyses, UV, ¹H-, and ¹³C-NMR spectra, products by hydrolysis with acid and yeast β-D-fructofuranosidase, migration on paper electrophoresis, and Gibbs reaction in the presence and absence of boric acid. Levansucrase from Microbacterium laevaniformans and yeast β-D-fructofuranosidase did not catalyze the β-D-fructofuranosyl transfer from sucrose to pyridoxine to give rise to β-D-fructofuranosyl-pyridoxine.