Showing papers on "Aspergillus niger published in 1995"

Solubilization of hardly-soluble AlPO4 with P-solubilizing microorganisms

Abstract: Four species Aspergillus niger, Penicillium simplicissimum, Pseudomonas sp. ( PI18 89 ) and Penicillium aurantiogriseum were found to be very effective in solubilizing hardly-soluble AlPO4. A. niger produced citrate, oxalate and gluconate, whereas the other species did not produce any organic acid in detectable amounts. This indicates that the production of organic acids is an important solubilization mechanism of AlPO4 but not the only effective one—as supposed in the great majority of publications. Nevertheless, organic acids alone are able to solubilize AlPO4 to a certain extent, although they are less effective compared to biotic leaching. Proton-excretion accompanying NH4+-assimilation is thought to be the most probable explanation for microbial solubilization without acid production. In hydroponic studies with P-solubilizing microorganisms, the plant Lepidium sativum and AlPO4 as the sole P source led to an increase in the dry weight and Al-content of plants. Plant P-content increased only when P. simplicissimum was inoculated.

Release of ferulic acid from wheat bran by a ferulic acid esterase (FAE-III) from Aspergillus niger

Abstract: Ferulic acid was efficiently released from a wheat bran preparation by a ferulic acid esterase from Aspergillus niger (FAE-III) when incubated together with a Trichoderma viride xylanase (a maximum of 95% total ferulic acid released after 5 h incubation). FAE-III by itself could release ferulic acid but at a level almost 24-fold lower than that obtained in the presence of the xylanase (2 U). Release of ferulic acid was proportional to the FAE-III concentration between 0.1 U and 1.3 U, but the presence of low levels of xylanase (0.1 U) increased the amount of ferulic acid released 6-fold. Total sugar release was not influenced by the action of FAE-III on the wheat bran, but the rate of release of the apparent end-products of xylanase action (xylose and xylobiose) was elevated by the presence of the esterase. The results show that FAE-III and the xylanase act together to break down feruloylated plant cell-wall polysaccharides to give a high yield of ferulic acid.

Stable accumulation of Aspergillus niger phytase in transgenic tobacco leaves

Abstract: Phytase from Aspergillus niger increases the availability of phosphorus from feed for monogastric animals by releasing phosphate from the substrate phytic acid. A phytase cDNA was constitutively expressed in transgenic tobacco (Nicotiana tabacum) plants. Secretion of the protein to the extracellular fluid was established by use of the signal sequence from the tobacco pathogen-related protein S. The specific phytase activity in isolated extracellular fluid was found to be approximately 90-fold higher than in total leaf extract, showing that the enzyme was secreted. This was confirmed by use of immunolocalization. Despite differences in glycosylation, specific activities of tobacco and Aspergillus phytase were identical. Phytase was found to be biologically active and to accumulate in leaves up to 14.4% of total soluble protein during plant maturation. Comparison of phytase accumulation and relative mRNA levels showed that phytase stably accumulated in transgenic leaves during plant growth.

Production and properties of three pectinolytic activities produced by Aspergillus niger in submerged and solid-state fermentation

Abstract: Three extracellular pectinases were produced byAspergillus niger CH4 by submerged and solid-state fermentation, and their physicochemical and kinetic properties were studied. The highest productivities of endo- and exo-pectinase and pectin lyase were obtained with solid-state fermentation. The kinetic and physicochemical properties of these enzymes were influenced by the type of culture method used. All activities were very different in terms of pH and temperature optima, stability at different pH and temperature values and affinity for the substrate (K m values). In solid-state fermentation, all pectinase activities were more stable at extreme pH and temperature values but theK m values of endo-pectinase and pectin lyase were higher with respect to those activities obtained by the submerged-culture technique. The pectin lyase activity obtained by the submerged-culture technique showed substrate inhibition but the enzyme obtained by solid-state fermentation did not. Electrophoresis, using sodium dodecyl sulphate/polyacrylamide gel with enzymatic extracts obtained for both culture methods, showed the same number on protein bands but some differences were found in their electrophoretic position. The results obtained in this work suggest that the culture method (submerged or solid-state) may be responsible for inducing changes in some of the pectinolytic enzymes produced byA. niger.

Production of raw starch digesting amylase by Aspergillus niger grown on native starch sources

Abstract: Aspergillus niger isolated from rotting cassava produced raw starch degrading amylase on cassava, maize, sorghum and soluble potato-derived starch as the sole carbon source without prior gelatinisation. Maximum activity of the amylase was attaired using cassava starch as substrate. The crude enzyme solution which comprised a mixture of raw and non raw starch digesting amylase degraded both cereal and tuber or root starches significantly. Source of assay starch significantly influenced raw starch digesting activity. Optimum pH for the raw starch degrading and the extracellular amylase were 6.0 and 3.5-4.0, respectively. However, both enzyme activities appeared to be uninfluenced across a relatively broad pH range 3.0-7.0. No correlation was found between the capacity of starch to induce expression of the enzyme and its susceptibility to enzyme digestion. The adsorbability of the various starches to raw starch digesting amylase was directly related to their digestibility.

Polyol pools in Aspergillus niger

Abstract: The accumulation and excretion of polyols was investigated under various growth conditions and at different stages of the life cycle of Aspergillus niger. Glycerol was found to be the major solute in osmotic adjustment of the hyphae. Conidiospores contain large amounts of mannitol, which are rapidly metabolized during early germination, leading to the accumulation of glycerol. Glycerol is the major polyol in young mycelium, whereas in older mycelium mannitol and erythritol predominate. In all experiments, polyols were also excreted. The mechanism and function of this process is unknown, but it might be a way to control the levels of the intracellular polyol pools. Polyols are rapidly taken up again upon starvation. In a glycerol kinase mutant the synthesis of glycerol is unaffected but the excreted level of the polyol is higher. This glycerol is taken up again upon starvation, and accumulates intracellularly as it can not be metabolized further.

Influence of different xylanases on the activity of ferulic acid esterase on wheat bran

Abstract: The apparent specific activity of ferulic acid esterases on cell wall polysaccharide materials is enhanced by the presence of xylanases. In this paper we show that the extent of the synergy between an Aspergillus niger ferulic acid esterase (FAE-III) and various xylanases [β-(1,4)-D-xylan xylanohydrolases (EC 3.2.1.8)] in releasing ferulic acid from de-starched wheat bran is strongly dependent on the source of the xylanase. Differences among the xylanases are found to be due to (a) the rate of hydrolysis of wheat bran cell wall polysaccharides and (b) the size distribution and nature of the products solubilized in the hydrolysis. In addition, analysis of the low-molecular-mass carbohydrate products indicates that the initial rate of the hydrolysis by the xylanase is also enhanced by the addition of the esterase, showing a reciprocal co-operation between the enzymes.

Rock phosphate solubilization by Aspergillus niger grown on sugar-beet waste medium

Abstract: Solubilization of rock phosphate by Aspergillus niger was studied in solid-state fermentation on sugar-beet waste. This combination was selected after testing three agroindustrial waste materials, namely rice hulls, sugar-beet waste and alperujo. Sugar-beet waste was the best substrate for fungal growth with 69% mineralization, followed by rice hulls and alperujo. The fungus was successfully cultivated on sugar-beet waste supplemented with 3.0 g/l rock phosphate, acidifying the medium and thus decreasing the pH to 3–3.5. Solubilization of insoluble phosphate increased during the first half of the process, reaching a maximum of 292 μg phosphate/ml, although a part of it was probably consumed by the mycelium.

Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae.

Abstract: An Aspergillus niger endopolygalacturonase (EC 3.2.1.15) cDNA was expressed in the yeast Saccharomyces cerevisiae. Secretion of the protein into the growth medium was efficiently directed by the fungal leader sequence, and processing occurred at the same site as in Aspergillus. The expression level was significantly enhanced by using a “short” version of the yeast ADHI promoter. An additional increase in the yield of heterologous protein was due to a higher plasmid stability and a rise in plasmid copy number. This was achieved by deleting most of the bacterial sequences from the expression vector. The yeast-derived enzyme showed the same enzymatic and biochemical properties as the fungal polygalacturonase, such as substrate specificity, pH and temperature optima and pI value. The yeast-derived enzyme, however, showed a higher degree of glycosylation and exhibited a more pronounced temperature stability than the fungal enzyme.

Citric acid and polyols production by Aspergillus niger at high glucose concentration in solid state fermentation on inert support

Abstract: Aspergillus niger cultures at high initial glucose concentration (up to 400 g/1) on Amberlite as inert support were carried out. Citric acid was accumulated in the support showing high concentration (94.54 g/l) and productivity (1.35 g/l h) without inhibition related to the presence of metals (Mn2+, Zn2+, Co2+, Cu2+, and Ca2+) at high concentrations. Citric acid accumulation was clearly associated with both, glycerol production and to the age of the culture. Glycerol and erythritol, the major osmoregulator metabolites, were also produced (8.16 and 24.57 g/l respectively) at 400 g/l of glucose.

Identification and elimination by site-directed mutagenesis of thermolabile aspartyl bonds in Aspergillus awamori glucoamylase

Abstract: Both native Aspergillus niger glucoamylase and wild-type Aspergillus awamori glucoamylase expressed in Saccharomyces cerevisiae, which have identical primary structures, undergo hydrolysis at aspartyl bonds at low pH values and elevated temperatures. In native A.niger enzyme the Asp126-Gly127 bond was preferentially cleaved at pH 3.5, while at pH 4.5 cleavage of the Asp257-Pro258 and Asp293-Gly294 bonds was dominant. In wild-type A.awamori glucoamylase, cleavage of the latter was dominant at both pH 3.5 and 4.5. Site-directed mutations Asp126-->Glu and Gly127-->Ala in wild-type enzyme decreased specific activities by approximately 60 and 30%, respectively, and increased irreversible thermoinactivation rates 3- to 4-fold at pH 4.5. Replacement of Asp257 with Glu and Asp293 with Glu or Gln decreased specific activities by approximately 20%, but greatly reduced cleavage of the Asp257-Pro258 and Asp293-Gly294 bonds. The Asp257-->Glu mutant was produced very slowly and was more thermostable than wild-type glucoamylase at pH 4.5 up to 70 degrees C. Replacement of Asp293 with either Glu or Gln significantly raised protein production and slightly increased thermostability at pH 3.5 and 4.5, but not at pH 5.5.

Purification and characterization of invertase from Aspergillus niger

Abstract: Invertase produced by a strain of Aspergillus niger showed the following main characteristics: maximum activity at 60°C, pH 5.0; Km with sucrose as substrate, 0.0625mm; Vmax 0.013 mol/min; and free energy 9132 cal/mol. The metal ions and p-chloromercuribenzoate (PCMB) acted as inhibitors respectively.

The isolation of Ant1, a transposable element from Aspergillus niger.

Abstract: A transposable element has been isolated from the industrially important fungus Aspergillus niger (strain N402). The element was identified as an insertion sequence within the coding region of the nitrate reductase gene. It had inserted at a TA site and appeared to have duplicated the target site upon insertion. The isolated element was found to be 4798 by in length and contained 37-bp inverted, imperfect, terminal repeats (ITRs). The sequence of the central region of the element revealed an open reading frame (designated ORF1) which showed similarity, at the amino acid level, to the transposase of the Tc1/mariner class of DNA transposons. Another sequence within the central region of the element showed similarity to the 3′ coding and downstream untranslated region of the amyA gene of A. niger. Sequence homology and structural features indicate that this element, which has been named Ant1 (A. niger transposon 1), is related to the Tc1/mariner group of DNA transposons. Ant1 is apparently present as a single copy in strain N402 of A. niger.

The Nitrate Reductase Gene from a Shoyu Koji Mold, Aspergillus oryzae KBN616

Abstract: A niaD gene encoding nitrate reductase was isolated from Aspergillus oryzae KBN616 and sequenced. The structural gene comprises 2973 bp and 868 amino acids, which showed a high degree of similarity to nitrate reductases from other filamentous fungi. The coding sequence is interrupted by six introns varying in size from 48 to 98 bp. The intron positions are all conserved among the niaD genes from A. oryzae, Aspergillus nidulans, and Aspergillus niger. A homologous transformation system was developed for an industrial shoyu koji mold, A. oryzae KBN616, based on the nitrate reductase (niaD) of the nitrate assimilation pathway.

Interaction between Aspergillus niger van Tiegh. and Glomus mosseae. (Nicol. & Gerd.) Gerd. & Trappe.

Abstract: SUMMARY Percent germination and length of hyphae of germinated Glomus mosseae spores, cultivated on water agar, decreased significantly in the presence of Aspergillus niger; this decrease was independent of any change in pH of the medium. Soluble and volatile compounds produced by A. niger significantly decreased percentage spore germination and the hyphal length of G. mosseae on water agar. The decrease caused by volatile compounds was significantly greater when A. niger was grown on malt extract agar. Shoot dry weights of maize and lettuce plants cultivated in soil in pots, and percentage arbuscular mycorrhizal (AM) root colonization of plants grown either in sand: vermiculite tubes inoculated with G. mosseae spores or in soil in pots with soil inoculum, were unaffected by A. niger when this saprobe was inoculated 2 wk after G. mosseae. Shoot dry weights and percentage AM colonization of plants decreased when the saprobic fungus was inoculated at the same time or 2 wk before G. mosseae. However, the metabolic activity resulting from AM colonization, measured as the percentage of mycelium showing succinate dehydrogenase activity, decreased in all treatments. The population of A. niger decreased when inoculated to the rhizosphere of plants at the same time as, or 2 wk after, G. mosseae, but not when it was inoculated 2 wk before G. mosseae. Our results show that G. mosseae decreases the saprobic fungal population through its effect on the plant, whereas A. niger, by the production of soluble or volatile substances, inhibits G. mosseae in its extramatrical stage.

Structure-Function Relationship of Acyl Amino Acid Surfactants: Surface Activity and Antimicrobial Properties

Abstract: Amino acid surfactants (AAS), having the general structure α-amino-(N-acyl)-β-alkoxypropionate, were synthesized chemically. Surface activity and antimicrobial properties of the AAS were evaluated. Increases in acyl chain length (i.e., C 10 -C 14 ) resulted in a linear reduction in surface tension (i.e., 43-36 mN.m -1 ), as well as dramatic decreases in critical micelle concentrations (cmc) (i.e., 17.9-0.43 mM). Strong correlations existed between the cmc of AAS and their minimal inhibitory concentrations (mic) against Escherichia coli, Pseudomonas aeruginsa, Aspergillus niger, and Saccharomyces cerevisiae. Sensitivity of the microorganisms to the various AAS followed the order Staphylococcus aureus>A. niger=S. cerevisiae E. coli P. aeruginosa. In comparison with methyl p-hydroxybenzoate, AAS (MN14) showed 2-8, 64, and 4-8 times the activity against Gram-negative bacteria, Gram-positive bacteria, and fungi, respectively. Surface adsorption and or bifunctional binding to the cell membrane may account for AAS action on microorganisms

The effects of agitation and aeration on the production of gluconic acid by Aspergillus niger

Abstract: The effects of agitation and aeration in the production of gluconic acid by Aspergillus niger from a glucose medium were investigated. Experiments were conducted at aeration rates of 5.0 and 10.0 L/min. Four different agitation speeds were investigated for each aeration rate. Gluconic acid concentration and biomass concentration were analyzed, and the rate of consumption of substrate by A. niger was noted. The main purpose of this work was to find the optimal conditions of agitation and aeration for the growth of A. niger and production of gluconic acid in submerged culture in a batch fermentor at a bench-top scale. The oxygen-transfer rates at different agitation and aeration rates were calculated. The gluconic acid concentration and rate of growth of A. niger increased with increase in the agitation and aeration rates.