Showing papers on "Aspergillus niger published in 2000"

Purification and Characterization of Novel Antifungal Compounds from the Sourdough Lactobacillus plantarum Strain 21B

Abstract: Sourdough lactic acid bacteria were selected for antifungal activity by a conidial germination assay. The 10-fold-concentrated culture filtrate of Lactobacillus plantarum 21B grown in wheat flour hydrolysate almost completely inhibited Eurotium repens IBT18000, Eurotium rubrum FTDC3228, Penicillium corylophilum IBT6978, Penicillium roqueforti IBT18687, Penicillium expansum IDM/FS2, Endomyces fibuliger IBT605 and IDM3812, Aspergillus niger FTDC3227 and IDM1, Aspergillus flavus FTDC3226, Monilia sitophila IDM/FS5, and Fusarium graminearum IDM623. The nonconcentrated culture filtrate of L. plantarum 21B grown in whole wheat flour hydrolysate had similar inhibitory activity. The activity was fungicidal. Calcium propionate at 3 mg ml(-1) was not effective under the same assay conditions, while sodium benzoate caused inhibition similar to L. plantarum 21B. After extraction with ethyl acetate, preparative silica gel thin-layer chromatography, and chromatographic and spectroscopic analyses, novel antifungal compounds such as phenyllactic and 4-hydroxy-phenyllactic acids were identified in the culture filtrate of L. plantarum 21B. Phenyllactic acid was contained at the highest concentration in the bacterial culture filtrate and had the highest activity. It inhibited all the fungi tested at a concentration of 50 mg ml(-1) except for P. roqueforti IBT18687 and P. corylophilum IBT6978 (inhibitory concentration, 166 mg ml(-1)). L. plantarum 20B, which showed high antimold activity, was also selected. Preliminary studies showed that phenyllactic and 4-hydroxy-phenyllactic acids were also contained in the bacterial culture filtrate of strain 20B. Growth of A. niger FTDC3227 occurred after 2 days in breads started with Saccharomyces cerevisiae 141 alone or with S. cerevisiae and Lactobacillus brevis 1D, an unselected but acidifying lactic acid bacterium, while the onset of fungal growth was delayed for 7 days in bread started with S. cerevisiae and selected L. plantarum 21B.

Phosphate-solubilizing microorganisms associated with the rhizosphere of mangroves in a semiarid coastal lagoon

Abstract: The phosphate-solubilizing potential of the rhizosphere microbial community in mangroves was de- monstrated when culture media supplemented with in- soluble, tribasic calcium phosphate, and incubated with roots of black (Avicennia germinans L.) and white (La- guncularia racemosa (L.) Gaertn.) mangrove became transparent after a few days of incubation. Thirteen phosphate-solubilizing bacterial strains were isolated from the rhizosphere of both species of mangroves: Ba- cillus amyloliquefaciens, Bacillus licheniformis, Bacillus atrophaeus, Paenibacillus macerans, Vibrio proteolyti- cus, Xanthobacter agilis, Enterobacter aerogenes, Ente- robacter taylorae, Enterobacter asburiae, Kluyvera cryo- crescens, Pseudomonas stutzeri, and Chryseomonas lu- teola. One bacterial isolate could not be identified. The rhizosphere of black mangroves also yielded the fungus Aspergillus niger. The phosphate-solubilizing activity of the isolates was first qualitatively evaluated by the for- mation of halos (clear zones) around the colonies grow- ing on solid medium containing tribasic calcium phos- phate as a sole phosphorus source. Spectrophotometric quantification of phosphate solubilization showed that all bacterial species and A. niger solubilized insoluble phosphate well in a liquid medium, and that V. proteo- lyticus was the most active solubilizing species among the bacteria. Gas chromatographic analyses of cell-free spent culture medium from the various bacteria de- monstrated the presence of 11 identified, and several unidentified, volatile and nonvolatile organic acids. Those most commonly produced by different species were lactic, succinic, isovaleric, isobutyric, and acetic acids. Most of the bacterial species produced more than one organic acid whereas A. niger produced only suc- cinic acid. We propose the production of organic acids by these mangrove rhizosphere microorganisms as a possible mechanism involved in the solubilization of in- soluble calcium phosphate.

Components of organic phosphorus in soil extracts that are hydrolysed by phytase and acid phosphatase.

Abstract: Extracts were prepared from soil using water, 50 mM citric acid (pH ∼2.3) or 0.5 M NaHCO3 (pH 8.5), and were incubated with excess phytase from Aspergillus niger to determine the amounts of labile P. Two A. niger phytase preparations were used: (1) a purified form which exhibited a narrow substrate specificity and high specific activity against phytate; and (2) a commercial preparation (Sigma) with activity against a broad range of P compounds. A comparatively large proportion (up to 79%, or 5.7 μg g–1 soil) of the organic P (Po) extracted with citric acid was hydrolysed by the commercial phytase, while between 28% and 40% (up to 3.1 μg g–1 soil) was hydrolysed using purified phytase. By comparison, only small quantities of the Po in water and NaHCO3 soil extracts were enzyme labile. While extractable Po was increased both with increasing concentrations of citric acid (up to 50 mM) and increasing pH (pH 2.3–6.0), enzyme-labile P increased only with citric acid concentration. The labile component of Po in citric acid extracts from soils with contrasting fertiliser histories indicated that enzyme-labile Po is a relatively large soil P pool and is potentially an important source of P for plants.

Inactivation of food-borne enteropathogenic bacteria and spoilage fungi using pulsed-light

Abstract: The lethality of high-intensity pulsed-light emissions from low and high ultraviolet (UV) light sources on predetermined microbial populations has been investigated. Prior to treatment, the bacterial enteropathogens Bacillus cereus, Escherichia coli, and Salmonella enteritidis and the food-spoilage fungi Aspergillus niger and Fusarium culmorum were seeded separately onto the surface of either tryptone soya yeast extract or malt extract agar plates. Prescribed microbial population densities were applied to the test media and these samples were exposed to one of two light sources. These were low-pressure, xenon filled, flash lamps that produced either high or low UV intensities. They were operated in pulsed mode, being driven by a stacked Blurnlein table generator. Microbial samples were treated by exposure to different numbers of light pulses. The treated bacterial populations were reduced by /spl sim/8 log orders after 1000 light-pulses of the higher UV intensity light and the fungal counts had a corresponding reduction of 4.5 log orders. The fungus, Aspergillus niger, was shown to be significantly more resistant in spore form to the intense UV light compared with Fusarium culmorum. This resistance has been attributed to the high level of UV absorbance associated with the dark pigment present in A. niger. The pulsed light source of lower UV intensity was shown to be significantly less effective in reducing microbial populations.

Bioactivation of poorly soluble phosphate rocks with a phosphorus-solubilizing fungus

Abstract: Many studies have demonstrated ineffectiveness of finely ground phosphate rock (PR) use due to the low solubility of its P contents This study was conducted to develop a simple, effective, and environmentally sound process to improve P availability of PR to crops by using a phosphate-solubilizing fungus (PSF), Aspergillus niger BCC F194,isolated from tropical acid soils The optimum incubation period and the optimum level of PR were determined The P-solubilizing effect of the supernatant of 9-d-old liquid culture supernatant (LCS) of the fungus was also determined by reacting it at various concentrations with Morrocan phosphate rock (MPR) The inoculation of the growth media with the PSF A niger resulted in the highest P solubility of the rock after 9 d of culturing at 25 g L -1 MPR Up to a certain degree, direct inoculation of fungal biomass and its LCS onto MPR caused a remarkable increase in 2% citric acid-soluble P, but not in water-soluble P content The possibilities of using the LCS instead of H 2 SO 4 in superphosphate (SP) production and using both with lower H 3 PO 4 concentrations were investigated with MPR as raw materials Replacement of H 2 SO 4 by the LCS in the SP production process yielded a comparable 2% citric acid-soluble P content Combining the LCS and H 2 SO 4 reduced the consumption of H 3 PO 4 that occurs in standard SP production This LCS technique provides a practical means for an effective bioactivation of PR intended for both as a P fertilizer and a raw material of the SP

Biosorption of Chromium, Copper, Nickel and Zinc Ions onto Fungal Pellets of Aspergillus niger 405 from Aqueous Solutions

Abstract: Fungal mycelium pellets of Aspergillus niger 405 has been used for adsorption of different metals. The biosorption of copper(II), zinc(II), nickel(II) and chromium(VI) is being studied over a range off metal ion concentrations, adsorption time, pH and co-anions. The process of uptake obeyed both the Langmuir and Freundlich isotherms. The results showed better biosorption for the first three metal ions between pH 4 and 6. On the contrary, pH values over a range of 3 to 7 had no influence on sorption of chromium. Comparison of metal uptake in single and multi-component aqueous solutions of Cu-Zn-Ni-Cr have been also undertaken. Fungus Aspergillus niger 405 showed a good affinity for binding of Cu2+, Zn2+ and Ni2+ in single and multicomponent-equimass solution, while in multi-component solution it occurred only for copper and zinc.

The Aspergillus niger transcriptional activator XlnR, which is involved in the degradation of the polysaccharides xylan and cellulose, also regulates d‐xylose reductase gene expression

Abstract: Screening of an Aspergillus niger differential cDNA library, constructed by subtracting cDNA fragments of a xlnR loss-of-function mutant from wild-type cDNA fragments, resulted in the cloning of the gene encoding d-xylose reductase (xyrA). Northern blot analysis using an A. niger wild-type strain, a xlnR multiple-copy strain and a xlnR loss-of-function mutant confirmed that the xyrA gene is regulated by XlnR, the transcriptional activator of the xylanolytic enzyme system in A. niger. d-xylose reductase catalyses the NADPH-dependent reduction of d-xylose to xylitol, which is the first step in d-xylose catabolism in fungi. Until now, XlnR was shown to control the transcription of genes encoding extracellular hydrolytic enzymes involved in cellulose and xylan degradation. In the present study, we show that A. niger is able to harmonize its sugar metabolism and extracellular xylan degradation via XlnR by regulating the expression of XyrA.

Studies on the Production of Fungal Peroxidases in Aspergillus niger

Abstract: To get insight into the limiting factors existing for the efficient production of fungal peroxidase in filamentous fungi, the expression of the Phanerochaete chrysosporium lignin peroxidase H8 (lipA) and manganese peroxidase (MnP) H4 (mnp1) genes in Aspergillus niger has been studied. For this purpose, a protease-deficient A. niger strain and different expression cassettes have been used. Northern blotting experiments indicated high steady-state mRNA levels for the recombinant genes. Manganese peroxidase was secreted into the culture medium as an active protein. The recombinant protein showed specific activity and a spectrum profile similar to those of the native enzyme, was correctly processed at its N terminus, and had a slightly lower mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Recombinant MnP production could be increased up to 100 mg/liter upon hemoglobin supplementation of the culture medium. Lignin peroxidase was also secreted into the extracellular medium, although the protein was not active, presumably due to incorrect processing of the secreted enzyme. Expression of the lipA and mnp1 genes fused to the A. niger glucoamylase gene did not result in improved production yields.

Screening of commercial hydrolases for the degradation of Ochratoxin A

Abstract: Ochratoxin A (OTA) is a nephrotoxic and carcinogenic mycotoxin. The toxin is a common contaminant of various foods and feeds and poses a serious threat to the health of both humans and animals. A number of commercial hydrolases were screened for the ability to degrade OTA to nontoxic compounds. A crude lipase from Aspergillus niger (Amano A) proved to substantially hydrolyze OTA to the nontoxic OTalpha and phenylalanine, as confirmed by HPLC with fluorescence detection. The enzyme was purified by anion exchange chromatography to homogeneity. Activity staining of the purified enzyme with alpha-naphthyl acetate/Fast Red revealed only one band exhibiting hydrolytic activity. The specific activity of the purified enzyme toward OTA was 2.32 units/mg.

Citric and gluconic acid production from fig by Aspergillus niger using solid-state fermentation.

Abstract: The production of citric and gluconic acids from fig by Aspergillus niger ATCC 10577 in solid-state fermentation was investigated. The maximal citric and gluconic acids concentration (64 and 490 g/kg dry figs, respectively), citric acid yield (8%), and gluconic acid yield (63%) were obtained at a moisture level of 75%, initial pH 7.0, temperature 30°C, and fermentation time in 15 days. However, the highest biomass dry weight (40 g/kg wet substrate) and sugar utilization (90%) were obtained in cultures grown at 35°C. The addition of 6% (w/w) methanol into substrate increased the concentration of citric and gluconic acid from 64 and 490 to 96 and 685 g/kg dry fig, respectively. Journal of Industrial Microbiology & Biotechnology (2000) 25, 298–304.

Induction of the soybean phytoalexins coumestrol and glyceollin by Aspergillus.

Abstract: Several isoflavonoid phytoalexins produced by soybeans are known to be estrogenic, with potential beneficial health effects in humans. Increased production of phytoalexins by the soybean plant will facilitate research efforts in this area. In this study, phytoalexin induction and accumulation in soybean cotyledon tissue was observed using four species of Aspergillus: A. sojae, A. oryzae, A. niger, and A. flavus. All four Aspergillus species tested elicited phytoalexin accumulation in living soybean cotyledons. Results from a time course study indicated that maximum concentrations of the phytoalexin glyceollin, 955 μg/g fresh weight (fw), occurred at day 3 in soybean cotyledon tissue inoculated with A. sojae. Other Aspergillus species caused an accumulation of glyceollin at significantly lower levels. A maximum concentration of coumestrol of 27.2 μg/g fw was obtained from soybean cotyledons inoculated with A. niger. Soybean phytoalexins induced by food-grade A. sojae and A. oryzae allowed the collection o...

β-Glucosidases from Five Black Aspergillus Species: Study of Their Physico-Chemical and Biocatalytic Properties

Abstract: Five black Aspergillus strains (A. aculeatus, A. foetidus, A. japonicus, A. niger, and A. tubingensis) were cultivated on crude wheat arabinoxylan as the carbon source under defined pH, temperature, and oxygen conditions. Protein and beta-glucosidase content differed remarkably within the obtained culture filtrates, of which eleven beta-glucosidases were isolated. Seven beta-glucosidases were purified to apparent electrophoretic homogeneity using anion-exchange and gel-permeation chromatography. They were found to be acidic proteins and most of them appeared to be glycoproteins with a molecular mass between 93 and 142 kDa. Classification of the beta-glucosidases into four groups (I-A, I-B, II, and III) is suggested according to their physicochemical and biocatalytic properties. The major beta-glucosidases were assigned to groups I-A and I-B, the minor beta-glucosidases to groups II and III, comprising acid-tolerant and glucose-tolerant enzymes, respectively.