Biotransformation of soy flour isoflavones by Aspergillus niger NRRL 3122 β-glucosidase enzyme

Characterization of a novel cold-adapted GH1 β-glucosidase from Psychrobacillus glaciei and its application in the hydrolysis of soybean isoflavone glycosides

The novel β-glucosidase gene (pgbgl1) of glycoside hydrolase (GH) family 1 from the psychrotrophic bacterium Psychrobacillus glaciei sp. PB01 was successfully expressed in Escherichia coli BL21 (DE3). The deduced PgBgl1 contained 447 amino acid residues with a calculated molecular mass of 51.4 kDa. PgBgl1 showed its maximum activity at pH 7.0 and 40 °C, and still retained over 10% activity at 0 °C, suggesting that the recombinant PgBgl1 is a cold-adapted enzyme. The substrate specificity, Km, Vmax, and Kcat/Km for the p-Nitrophenyl-β-D-glucopyranoside (pNPG) as the substrate were 1063.89 U/mg, 0.36 mM, 1208.31 U/mg and 3871.92/s, respectively. Furthermore, PgBgl1 demonstrated remarkable stimulation of monosaccharides such as glucose, xylose, and galactose, as well as NaCl. PgBgl1 also demonstrated a high capacity to convert the primary soybean isoflavone glycosides (daidzin, genistin, and glycitin) into their respective aglycones. Overall, PgBgl1 exhibited high catalytic activity towards aryl glycosides, suggesting promising application prospects in the food, animal feed, and pharmaceutical industries.

Physiological and metabolic traits of Taxol biosynthesis of endophytic fungi inhabiting plants: Plant-microbial crosstalk, and epigenetic regulators

Attenuating the Taxol productivity of fungi with the subculturing and storage under axenic conditions is the challenge that halts the feasibility of fungi to be an industrial platform for Taxol production. This successive weakening of Taxol productivity by fungi could be attributed to the epigenetic down-regulation and molecular silencing of most of the gene clusters encoding Taxol biosynthetic enzymes. Thus, exploring the epigenetic regulating mechanisms controlling the molecular machinery of Taxol biosynthesis could be an alternative prospective technology to conquer the lower accessibility of Taxol by the potent fungi. The current review focuses on discussing the different molecular approaches, epigenetic regulators, transcriptional factors, metabolic manipulators, microbial communications and microbial cross-talking approaches on restoring and enhancing the Taxol biosynthetic potency of fungi to be industrial platform for Taxol production.

Fungal biotransformation of carvone and camphor by Aspergillus flavus and investigation of cytotoxic activities of naturally obtained essential oils

In this study, the biotransformation of carvone and camphor by Aspergillus flavus and the products were investigated. The biotransformation reaction of carvone by A. flavus resulted in the production of neodihydrocarveol, dihydrocarvone, 2-cyclohexene-1-one,2-methyl-5-(1-methylethenyl), limonene-1,2-diol, trans-p-mentha-1(7),8-dien-2-ol, p-menth-8(10)-ene-2,9-diol, and the biotransformation reaction of camphor resulted in the production of 2 -campholenic acid, 2-cyclohexene-1-one,2-hydroxy-4,4,6,6-tetramethyl, α-campholene aldehyde. The naturally produced essential oils by biotransformation of carvone and camphor were observed to be cytotoxic to breast cancer cells while no significant inhibition was seen in the healthy cell line. Additionally, biotransformation products had the highest inhibition (74%) against aflatoxin B1. The bioactivities of biotransformation products are promising, and they can be further investigated for their therapeutic potential as active agents.

Rhizopus oryzae Inulinase Production and Characterization with Application in Chicory Root Saccharification

The objective of this study was to create a fermentation process for the production of inulinase, an important enzyme with numerous applications in the food and pharmaceutical industries, using low-cost agricultural waste as substrates for Rhizopus oryzae NRRL 3563. High titer inulinase production in chicory roots by Rhizopus oryzae in a submerged culture was accomplished using a statistical experimental design. A two-level Plackett–Burman design followed by a three-level Box–Behnken design producing a high inulinase titer of 1085.11 U/mL, 2.83-fold the maximum level, was obtained in the screening experiment. The optimal levels were as follows: chicory root, 10 g/L; NaNO3, 5 g/L; and KCl, 0.2 g/L. The produced inulinase enzyme was purified using 70% ammonium sulfate precipitation and ultra-filtration causing 3.63-fold purification with 60% activity recovery. The enzyme had a molecular weight of approximately 130 KDa. The purified enzyme showed optimum activity at 50 °C and pH 6.0. The pH stability range was three to six and the temperature stability was up 70 °C. The purified inulinase could hydrolyze inulin and sucrose, but not cellobiose or soluble starch. Km and Vmax for inulin were determined to be 0.8 mg/mL and 50,000 U/mg, respectively. The two-level Plackett–Burman design was applied followed by a Box–Behnken model for optimization of fermentation conditions. Accordingly, the optimal combination of fermentation was a reaction time of seven hours, a temperature of 60 °C, and an enzyme concentration of 40,000 U/mL, which resulted in a 58.07% saccharification yield. The characteristics of the enzyme and its kinetic parameters suggested that it was highly effective in the fermentation of inulin and inulin-containing substrates. Additionally, it raises the potential of using inulinase enzymes in pharmaceutical and food industries.

Aspergillus Niger thermostable Cytosine deaminase-dextran conjugates with enhanced structure stability, proteolytic resistance, and Antiproliferative activity

Cytosine deaminase (CDA) is a prodrug mediating enzyme converting 5-flurocytosine into 5-flurouracil with profound broad-range anticancer activity towards various cell lines. Availability, molecular stability, and catalytic efficiency are the main limiting factors halting the clinical applications of this enzyme on prodrug and gene therapies, thus, screening for CDA with unique biochemical and catalytic properties was the objective. Thermotolerant/ thermophilic fungi could be a distinctive repertoire for enzymes with affordable stability and catalytic efficiency. Among the recovered thermotolerant isolates, Aspergillus niger with optimal growth at 45 °C had the highest CDA productivity. The enzyme was purified, with purification 15.4 folds, molecular mass 48 kDa and 98 kDa, under denaturing and native PAGE, respectively. The purified CDA was covalently conjugated with dextran with the highest immobilization yield of 75%. The free and CDA-dextran conjugates have the same optimum pH 7.4, reaction temperature 37 °C, and pI 4.5, and similar response to the inhibitors and amino acids suicide analogues, ensuring the lack of effect of dextran conjugation on the CDA conformational structure. CDA-Dextran conjugates had more resistance to proteolysis in response to proteinase K and trypsin by 2.9 and 1.5 folds, respectively. CDA-Dextran conjugates displayed a dramatic structural and thermal stability than the free enzyme, authenticating the acquired structural and catalytic stability upon dextran conjugation. The thermal stability of CDA was increased by about 1.5 folds, upon dextran conjugation, as revealed from the half-life time (T_1/2). The affinity of CDA-conjugates (K_m 0.15 mM) and free CDA (K_m 0.22 mM) to deaminate 5-fluorocytosine was increased by 1.5 folds. Upon dextran conjugation, the antiproliferative activity of the CDA towards the different cell lines "MDA-MB, HepG-2, and PC-3" was significantly increased by mediating the prodrug 5-FC. The CDA-dextran conjugates strongly reduce the tumor size and weight of the Ehrlich cells (EAC), dramatically increase the titers of Caspase-independent apoptotic markers PARP-1 and AIF, with no cellular cytotoxic activity, as revealed from the hematological and biochemical parameters.

Genome sequences of 24 Aspergillus niger sensu stricto strains to study strain diversity, heterokaryon compatibility, and sexual reproduction

Mating-type distribution within a phylogenetic tree, heterokaryon compatibility, and subsequent diploid formation were studied in 24 Aspergillus niger sensu stricto strains. The genomes of the 24 strains were sequenced and analyzed revealing an average of 6.1 ± 2.0 variants/kb between Aspergillus niger sensu stricto strains. The genome sequences were used together with available genome data to generate a phylogenetic tree revealing 3 distinct clades within Aspergillus niger sensu stricto. The phylogenetic tree revealed that both MAT1-1 and MAT1-2 mating types were present in each of the 3 clades. The phylogenetic differences were used to select for strains to analyze heterokaryon compatibility. Conidial color markers (fwnA and brnA) and auxotrophic markers (pyrG and nicB) were introduced via CRISPR/Cas9-based genome editing in a selection of strains. Twenty-three parasexual crosses using 11 different strains were performed. Only a single parasexual cross between genetically highly similar strains resulted in a successful formation of heterokaryotic mycelium and subsequent diploid formation, indicating widespread heterokaryon incompatibility as well as multiple active heterokaryon incompatibility systems between Aspergillus niger sensu stricto strains. The 2 vegetatively compatible strains were of 2 different mating types and a stable diploid was isolated from this heterokaryon. Sclerotium formation was induced on agar media containing Triton X-100; however, the sclerotia remained sterile and no ascospores were observed. Nevertheless, this is the first report of a diploid Aspergillus niger sensu stricto strain with 2 different mating types, which offers the unique possibility to screen for conditions that might lead to ascospore formation in A. niger.

Visual Sensing of β-Glucosidase From Intestinal Fungus in the Generation of Cytotoxic Icarisid II

β-Glucosidase (β-Glc) is an enzyme capable of the selective hydrolysis of the β-glycosidic bond of glycosides and glycans containing glucose. β-Glc expressed by intestinal microbiota has attracted increasing levels of interest, due to their important roles for the metabolism of exogenous substances in the gut. Using the 2-((6-hydroxy-2,3-dihydro-1H-xanthen-4-yl)methylene)malononitrile fluorophore (DXM-OH, λ_em 636 nm) and the recognition group β-Glucose, an enzymatic activatable turn-on fluorescent probe (DXM-Glc) was developed for the selective and sensitive sensing of β-Glc. In addition, DXM-Glc could be used to sense endogenous β-Glc in living fungal cells. Using DXM-Glc, Pichia terricola M2 was identified as a functional intestinal fungus with β-Glc expression. P. terricola M2 could transform the flavone glycoside Icariin to Icariside Ⅱ efficiently, which confirmed the metabolism of glycosides in the gut mediated by fungi. Furthermore, Icariside Ⅱ could inhibit the proliferation of human endometrial cancer cells (RL 95-2 and ishikawa) significantly, suggesting the metabolic activation of Icariin by intestinal fungi in vivo. Therefore, DXM-Glc as a probe for β-Glc provided a novel technique for the investigation of the metabolism of bioactive substances by intestinal microbiota.

Production, Bioprocessing and Anti-Proliferative Activity of Camptothecin from Penicillium chrysogenum, "An Endozoic of Marine Sponge, Cliona sp.", as a Metabolically Stable Camptothecin Producing Isolate

Exploring the metabolic potency of fungi as camptothecin producers raises the hope of their usage as an industrial source of camptothecin, due to their short-life span and the feasibility of metabolic engineering. However, the tiny yield and loss of camptothecin productivity of fungi during storage and sub-culturing are challenges that counteract this approach. Marine fungi could be a novel source for camptothecin production, with higher yield and reliable metabolic sustainability. The marine fungal isolate Penicillium chrysogenum EFBL # OL597937.1 derived from the sponge "Cliona sp." has been morphologically identified and molecularly confirmed, based on the Internal Transcribed Spacer sequence, exhibiting the highest yield of camptothecin (110 μg/L). The molecular structure and chemical identity of P. chrysogenum derived camptothecin has been resolved by HPLC, FTIR and LC-MS/MS analyses, giving the same spectroscopic profiles and mass fragmentation patterns as authentic camptothecin. The extracted camptothecin displayed a strong anti-proliferative activity towards HEP-2 and HCT-116 (IC₅₀ values 0.33-0.35 µM). The yield of camptothecin was maximized by nutritional optimization of P. chrysogenum with a Plackett-Burman design, and the productivity of camptothecin increased by 1.8 fold (200 µg/L), compared to control fungal cultures. Upon storage at 4 °C as slope culture for 8 months, the productivity of camptothecin for P. chrysogenum was reduced by 40% compared to the initial culture. Visual fading of the mycelial pigmentation of P. chrysogenum was observed during fungal storage, matched with loss of camptothecin productivity. Methylene chloride extracts of Cliona sp. had the potency to completely restore the camptothecin productivity of P. chrysogenum, ensuring the partial dependence of the expression of the camptothecin biosynthetic machinery of P. chrysogenum on the chemical signals derived from the sponge, or the associated microbial flora. This is the first report describing the feasibility of P. chrysogenum, endozoic of Cliona sp., for camptothecin production, along with reliable metabolic biosynthetic stability, which could be a new platform for scaling-up camptothecin production.

Production of Daidzein and Genistein from Seed and Root Extracts of Korean Wild Soybean (Glycine soja) by Thermostable β-Galactosidase from Thermoproteus uzoniensis

Isoflavone glycosides are commonly biotransformed into isoflavone aglycones due to the superior biological activities of the latter. Wild soybeans contain a higher isoflavone content than domesticated soybeans due to their high level of genetic diversity. In this study, we cloned and characterized a thermostable β-galactosidase from the extreme thermophile Thermoproteus uzoniensis for potential application in isoflavone conversion in Korean wild soybeans. The purified recombinant enzyme exhibited a maximum specific activity of 1103 μmol/min/mg at pH 5.0 and 90 °C with a half-life of 46 h and exists as a homodimer of 113 kDa. The enzyme exhibited the highest activity for p-nitrophenyl (pNP)-β-D-galactopyranoside among aryl glycosides and it hydrolyzed isoflavone glycosides in the order genistin > daidzin > ononin > glycitin. The enzyme completely hydrolyzed 2.77 mM daidzin and 3.85 mM genistin in the seed extract of wild soybean after 80 and 70 min with productivities of 1.86 and 3.30 mM/h, respectively, and 9.89 mM daidzin and 1.67 mM genistin in the root extract after 180 and 30 min, with the highest productivities of 3.30 and 3.36 mM/h, respectively, compared to other glycosidases. Our results will contribute to the industrial production of isoflavone aglycone using wild soybean and this is the first report on the enzymatic production of isoflavone aglycones from isoflavone glycosides in wild soybeans.

Boosting the Anticancer Activity of Aspergillus flavus "endophyte of Jojoba" Taxol via Conjugation with Gold Nanoparticles Mediated by γ-Irradiation

Taxol production by fungi is one of the promising alternative approaches, regarding to the natural and semisynthetic sources; however, the lower yield and rapid loss of Taxol productivity by fungi are the major challenges that halt their further industrial implementation. Thus, searching for fungal isolates with affordable Taxol-production stability, in addition to enhance its anticancer activity via conjugation with gold nanoparticles, is the main objectives of this study. Twenty-four endophytic fungal isolates were recovered from the barks, twigs, and leaves of jojoba plant, among these fungi, Aspergillus flavus MW485934.1 was the most potent Taxol producer (88.6 µg/l). The chemical identity of the extracted Taxol of A. flavus was verified by the TLC, HPLC, HNMR, and FTIR analyses. The yield of Taxol produced by A. flavus was optimized by the response surface methodology (RSM) using Plackett-Burman (PBD) and faced central composite designs (FCCD). The yield of Taxol by A. flavus was increased by about 3.2 folds comparing to the control cultures (from 96.5 into 302.7 µg/l). The highest Taxol yield by was obtained growing A. flavus on a modified malt extract medium (g/l) (malt extract 20.0, peptone 2.0, sucrose 20.0, soytone 2.0, cysteine 0.5, glutamine 0.5, and beef extract 1.0 adjusted to pH 6.0) and incubated at 30 °C for 16 days. From the FCCD design, the significant variables affecting Taxol production by A. flavus were cysteine, pH, and incubation time. Upon A. flavus γ-irradiation at 1.0 kGy, the Taxol yield was increased by about 1.25 fold (375.9 µg/l). To boost its anticancer activity, the purified Taxol was conjugated with gold nanoparticles (AuNPs) mediated by γ-rays irradiation (0.5 kGy), and the physicochemical properties of Taxol-AuNPs composite were evaluated by UV-Vis, DLS, XRD, and TEM analyses. The IC₅₀ values of the native-Taxol and Taxol-AuNPs conjugates towards HEPG-2 cells were 4.06 and 2.1 µg/ml, while the IC₅₀ values against MCF-7 were 6.07 and 3.3 µg/ml, respectively. Thus, the anticancer activity of Taxol-AuNPs composite was increased by 2 folds comparing to the native Taxol towards HEPG-2 and MCF-7 cell lines. Also, the antimicrobial activity of Taxol against the multidrug resistant bacteria was dramatically increased upon conjugation with AuNPs comparing to authentic AuNPs and Taxol, ensuring the higher solubility, targetability, and efficiency of Taxol upon AuNPs conjugation.

Biosynthesis and Anti-Mycotoxigenic Activity of Zingiber officinale Roscoe-Derived Metal Nanoparticles

Mycotoxigenic fungi have attracted special attention due to their threat to food security and toxicity to human health. Aqueous extract of Zingiber officinale Roscoe was used as reducing and capping agent for the synthesis of silver (AgNPs), copper (CuNPs), and zinc oxide (ZnONPs) nanoparticles. UV-Visible spectra of the AgNPs, CuNPs, and ZnONPs showed absorption peaks at λmax 416 nm, 472 nm, and 372 nm, respectively. Zeta potential of AgNPs, CuNPs, and ZnONPs were -30.9, -30.4 and -18.4 mV, respectively. ZnONPs showed the highest activity against Aspergillus awamori ZUJQ 965830.1 (ZOI 20.9 mm and MIC 24.7 µg/mL). TEM micrographs of ZnONPs-treated A. awamori showed cracks and pits in the cell wall, liquefaction of the cytoplasmic content, making it less electron-dense. The sporulation and ochratoxin A production of A. awamori was inhibited by ZnONPs in a concentration-dependent pattern. The inhibition percentage of OTA were 45.6, 84.78 and 95.65% for 10, 15, 20 of ZnONPs/mL, respectively.

Microbial biotransformation of Pericarpium Citri Reticulatae (PCR) by Aspergillus niger and effects on antioxidant activity

Pericarpium Citri Reticulatae (PCR), the mature fruit peel of Citrus reticulata Blanco and its different cultivars, is an important citrus by-product with beneficial health and nutritive properties. However, due to the lack of value-added methods for its development and utilization, a large amount of PCR is discarded or wasted. To explore a possibly more effective method to utilize PCR, we compared the chemical and biological differences before (CK) and after (CP) microbial transformation of PCR by Aspergillus niger. UPLC-ESI-MS/MS, HPLC, and LC-MS methods were used to compare the chemical profiles of CK and CP. The results demonstrated that microbial biotransformation by A. niger could transform flavonoid compounds by utilizing the carbohydrate and amino acid nutrients in PCR. This could also promote the accumulation of polyhydroxyflavones compounds in CP. The antioxidant assay demonstrated that CP had significantly greater free radical-scavenging activity than CK. The higher antioxidant activity of CP may result from the high level of flavonoids with associated phenolic hydroxyl groups. Microbial biotransformation is an effective method for improving the antioxidant capacity of PCR and may be effective and useful in other natural product situations.