Essential oils are aromatic oily liquids obtained from some aromatic plant materials. Certain essential oils such as citronella oil contain antifungal activity, but the antifungal effect is still ...unknown. In this study, we explored the antifungal effect of citronella oil with
Aspergillus niger
ATCC 16404. The antifungal activity of citronella oil on conidia of
A
.
niger
was determined by poisoned food technique, broth dilution method, and disc volatility method. Experimental results indicated that the citronella oil has strong antifungal activity: 0.125 (
v
/
v
) and 0.25 % (
v
/
v
) citronella oil inhibited the growth of 5 × 10
5
spore/ml conidia separately for 7 and 28 days while 0.5 % (
v
/
v
) citronella oil could completely kill the conidia of 5 × 10
5
spore/ml. Moreover, the fungicidal kinetic curves revealed that more than 90 % conidia (initial concentration is 5 × 10
5
spore/ml) were killed in all the treatments with 0.125 to 2 % citronella oil after 24 h. Furthermore, with increase of citronella oil concentration and treatment time, the antifungal activity was increased correspondingly. The 0.5 % (
v
/
v
) concentration of citronella oil was a threshold to kill the conidia thoroughly. The surviving conidia treated with 0.5 to 2 % citronella oil decreased by an order of magnitude every day, and no fungus survived after 10 days. With light microscope, scanning electron microscope, and transmission electron microscope, we found that citronella oil could lead to irreversible alteration of the hyphae and conidia. Based on our observation, we hypothesized that the citronella oil destroyed the cell wall of the
A
.
niger
hyphae, passed through the cell membrane, penetrated into the cytoplasm, and acted on the main organelles. Subsequently, the hyphae was collapsed and squashed due to large cytoplasm loss, and the organelles were severely destroyed. Similarly, citronella oil could lead to the rupture of hard cell wall and then act on the sporoplasm to kill the conidia. Nevertheless, the citronella oil provides a potential of being a safe and environmentally friendly fungicide in the future.
Celotno besedilo
Dostopno za:
CEKLJ, DOBA, EMUNI, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK
Itaconic acid is a five-carbon dicarboxylic acid with an unsaturated alkene bond, frequently used as a building block for the industrial production of a variety of synthetic polymers. It is also one ...of the major products of fungal “overflow metabolism” which can be produced in submerged fermentations of the filamentous fungus
Aspergillus terreus
. At the present, molar yields of itaconate are lower than those obtained in citric acid production in
Aspergillus niger
. Here, we have studied the possibility that the yield may be limited by the oxygen supply during fermentation and hence tested the effect of the dissolved oxygen concentration on the itaconic acid formation rate and yield in lab-scale bioreactors. The data show that a dissolved oxygen concentration of 2% saturation was sufficient for maximal biomass formation. Raising it to 30% saturation had no effect on biomass formation or the growth rate, but the itaconate yield augmented substantially from 0.53 to 0.85 mol itaconate/mol glucose. Furthermore, the volumetric and specific rates of itaconic acid formation ameliorated by as much as 150% concurrent with faster glucose consumption, shortening the fermentation time by 48 h. Further increasing the dissolved oxygen concentration over 30% saturation had no effect. Moreover, we show that this increase in itaconic acid production coincides with an increase in alternative respiration, circumventing the formation of surplus ATP by the cytochrome electron transport chain, as well as with increased levels of alternative oxidase transcript. We conclude that high(er) itaconic acid accumulation requires a dissolved oxygen concentration that is much higher than that needed for maximal biomass formation, and postulate that the induction of alternative respiration allows the necessary NADH reoxidation ratio without surplus ATP production to increase the glucose consumption and the flux through overflow metabolism.
Summary The antifungal activity of bacteria from the genus Collimonas has been well documented, but the chemistry and gene functions that underlie this phenotype are still poorly understood. ...Screening of a random plasposon insertion library of Collimonas fungivoransTer331 for loss-of-function mutants revealed the importance of gene cluster K, which is annotated to code for the biosynthesis of a secondary metabolite and which features genes for fatty acid desaturases and polyketide synthases. Mutants in gene cluster K had lost the ability to inhibit hyphal growth of the fungus Aspergillus niger and were no longer able to produce and secrete several metabolites that after extraction and partial purification from wildtype strain Ter331 were shown to share a putative ene-triyne moiety. Some but not all of these metabolites were able to inhibit growth of A.niger, indicating functional variation within this group of Collimonas-produced polyyne-like 'collimomycins'. Polymerase chain reaction analysis of isolates representing different Collimonas species indicated that the possession of cluster K genes correlated positively with antifungal ability, further strengthening the notion that this cluster is involved in collimomycin production. We discuss our findings in the context of other bacterially produced polyynes and the potential use of collimomycins for the control of harmful fungi. PUBLICATION ABSTRACT
•Freeze dried mycelia of halotolerant A.niger was used as catalyst in ionic liquids.•CAPE synthesis reaction conditions were optimized.•CAPE synthesis yield of 80% was achieved in EmimTf2N.
Synthesis ...of caffeic acid ester essentially requires an efficient esterification process to produce various kinds of medicinally important ester derivatives. In the present study, a comprehensive and comparative analysis of whole-cell catalyzed caffeic acid esters production in ionic liquids (ILs) media was performed. Olive oil induced mycelial mass of halotolerant Aspergillus niger (A.niger) EXF 4321 was freeze dried and used as a catalyst. To ensure maximum solubilization of caffeic acid for highest substrate loading several ILs were screened and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmimTf2N) was found to have the maximum solubility and favoured for enzymatic activity of freeze dried mycelia. The whole-cell catalyzed synthesis of caffeic acid phenethyl ester (CAPE) conditions were optimized and bioconversion up to 84% was achieved at a substrate molar ratio of 1:20 (caffeic acid:2-phenyl ethanol), 30°C for 12h. Results obtained during this study were encouraging and helpful to design a bioreactor system to produce caffeic acid derived esters.
The genome of the filamentous fungus Aspergillus niger is rich in genes encoding pectinases, a broad class of enzymes that have been extensively studied due to their use in industrial applications. ...The sequencing of the A. niger genome provided more knowledge concerning the individual pectinolytic genes, but little is known about the regulatory genes involved in pectin degradation. Understanding regulation of the pectinolytic genes provides a tool to optimize the production of pectinases in this industrially important fungus. This study describes the identification and characterization of one of the activators of pectinase-encoding genes, RhaR. Inactivation of the gene encoding this regulator resulted in down-regulation of genes involved in the release of L-rhamnose from the pectin substructure rhamnogalacturonan I, as well as catabolism of this monosaccharide. The rhaR disruptant was unable to grow on L-rhamnose, but only a small reduction in growth on pectin was observed. This is likely caused by the presence of a second, so far unknown regulator that responds to the presence of D-galacturonic acid.
β-Glucanase has received great attention in recent years regarding their potential biotechnological applications and antifungal activities. Herein, the specific objectives of the present study were ...to purify, characterize and immobilize β-glucanase from Aspergillus niger using covalent binding and cross linking techniques. The evaluation of β-glucanase in hydrolysis of different lignocellulosic wastes with subsequent bioethanol production and its capability in biocontrol of pathogenic fungi was investigated. Upon nutritional bioprocessing, β-glucanase production from A. niger EG-RE (MW390925.1) preferred ammonium nitrate and CMC as the best nitrogen and carbon sources, respectively. The soluble enzyme was purified by (NH
)
SO
, DEAE-Cellulose and Sephadex G
with 10.33-fold and specific activity of 379.1 U/mg protein. Tyrosyl, sulfhydryl, tryptophanyl and arginyl were essential residues for enzyme catalysis. The purified β-glucanase was immobilized on carrageenan and chitosan with appreciable yield. However, the cross-linked enzyme exhibited superior activity along with remarkable improved thermostability and operational stability. Remarkably, the application of the above biocatalyst proved to be a promising candidate in liberating the associate lignocellulosic reducing sugars, which was utilized for ethanol production by Saccharomyces cerevisiae. The purified β-glucanase revealed an inhibitory effect on the growth of two tested phytopathogens Fusarium oxysporum and Penicillium digitatum.
Microbial assisted biosynthesis of nanoparticles is a rapidly progressing area of nanobiotechnology. In this paper
Aspergillus niger assisted extracellular synthesis of silver nanoparticles is ...reported. The silver nanoparticles were characterized by UV–vis spectrophotometry, TEM, EDX and FTIR. TEM studies showed the size of the silver nanoparticles to be in the range of 3–30
nm. The probable mechanism for the extracellular synthesis of silver nanoparticles by
Aspergillus niger was investigated. The nanoparticles showed antimicrobial activity against fungal and bacterial strains.
Aspergillus niger mycelial waste is a good raw material for production of N-acetyl-d-glucosamine (GlcNAc). In this study, AnChiB, an A. niger chitinase which is upregulated during autolysis, was ...found to degrade A. niger mycelial waste with high efficiency. It could produce 1.45 mM (GlcNAc)2 in 8 h from raw mycelial waste, outperforming other chitinases, including bacterial SmChiA, human HsCht, and insect OfChtI and OfChi-h. The crystal structure of AnChiB was determined, and residues Trp106 and Trp118 were found to be important for the activity of AnChiB toward mycelial waste; mutation of either Trp106 or Trp118 into phenylalanine or alanine resulted in dramatically decreased activity. A recombinant strain of Bacillus subtilis was constructed to extracellularly produce AnChiB, and the culture supernatant was used to treat mycelial waste. This eco-friendly strategy could produce 3.7 mM of GlcNAc from 10 g of mycelial waste in 94 h with a yield of 71.3%.
► New bioprocesses for the production of cellulolytic enzymes are needed. ► A novel combined cultivation method for cellulase production is being proposed. ► The new method resulted in a 3-fold ...improvement over conventional fermentation.
Sequential solid-state and submerged cultivation with sugarcane bagasse as substrate for cellulase production by Aspergillus niger A12 was assessed by measuring endoglucanase activity. An unconventional pre-culture with an initial fungal growth phase under solid-state cultivation was followed by a transition to submerged fermentation by adding the liquid culture medium to the mycelium grown on solid substrate. For comparison, control experiments were conducted using conventional submerged cultivation. The cultures were carried out in shake flasks and in a 5-L bubble column bioreactor. An endoglucanase productivity of 57±13IU/L/h was achieved in bubble column cultivations prepared using the new method, representing an approximately 3-fold improvement compared to conventional submerged fermentation. Therefore, the methodology proposed here of a sequential fermentation process offers a promising alternative for cellulase production.
Cellulolytic enzyme production by newly isolated Aspergillus niger HN-1 was statistically optimized using Plackett–Burman and central composite design (CCD). Optimum concentrations of 2, 0.40, 0.01, ...and 0.60 g L –1 for KH2PO4, urea, trace elements solution, and CaCl2·2H2O, respectively, were suggested by Design-Expert software. The two-stage optimization process led to a 3- and 2-fold increases in the filter paper cellulase (FP) and β-glucosidase activities, respectively. FP, β-glucosidase, endoglucanase, exopolygalaturonase, cellobiohydrolase, xylanase, α-l-arabinofuranosidase, β-xylosidase, and xylan esterase activities of 36.7 ± 1.54 FPU gds–1, 252.3 ± 7.4 IU gds–1, 416.3 ± 22.8 IU gds–1, 111.2 ± 5.4 IU gds–1, 8.9 ± 0.50 IU gds–1, 2593.5 ± 78.9 IU gds–1, 79.4 ± 4.3 IU gds–1, 180.8 ± 9.3 IU gds–1, and 288.7 ± 11.8 IU gds–1, respectively, were obtained through solid-state fermentation during the validation studies. Hydrolysis of alkali-treated rice straw with crude cellulases resulted in about 84% glucan to glucose, 89% xylan to xylose, and 91% arabinan to arabinose conversions, indicating potential for biomass hydrolysis by the crude cellulase consortium obtained in this study.
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