Cultures Of Aspergillus Flavus Research Articles

Phytotoxic effect of Carica papaya extract on seed-borne fungus of African Yam Bean (Sphenostylis stenocarpa Hochst ex. A. Rich. Harms) seeds

Extracts of many higher plants have been reported to exhibit antifungal properties under laboratory experiments. This study was therefore carried out to investigate the effect of Carica papaya plant extracts on the African Yam Bean seed-borne pathogen. The seed health test of African Yam Bean was carried out using the blotter paper method. The experiment was conducted at the Plant Pathology Laboratory of the Department of Crop Science and Horticulture, Nnamdi Azikiwe University, Awka. Test of plant extract for inhibition of radial growth of seed-borne pathogen of African yam bean was studied under in vitro experiment at 0%, 50%, 75% and 100% concentrations with 0% as the control. The design was a Completely Randomized Design (CRD) with three replications. The test plant extracts of different concentrations were added into Petri dishes containing molten-sterilized Sabouraud Dextrose Agar (SDA) and swayed gently on the laboratory bench to allow an even mixture These were allowed to gel. Then nine millimeter discs of a seven-day pure culture of Aspergillus flavus were aseptically placed on the centre of the Petri dishes containing the SDA-extract mixture. Records on the radial inhibition effect of the test plant extract were kept for further analysis. Data on radial inhibition of fungus were subjected to Analysis of Variance (ANOVA). Results showed that Aspergillus niger, Aspergillus flavus and Aspergillus terreus were isolated from incubated African Yam Bean seeds. Carica papaya leaf extract used was very effective and the higher the concentrations of extract, the more effective in the inhibition of radial growth of the test fungus. It could therefore be recommended that farmers should always conduct viability tests on procured seeds before planting. Farmers should rather use plant extract such as the one used in this experiment in controlling seed-borne fungal pathogens of African Yam Bean seeds than synthetic fungicides.

Exploration of aflatoxigenic potential and seed colonization of Aspergillus flavus in sunflower

Aflatoxin, a mycotoxin found commonly in maize, peanuts, and sunflower worldwide, is associated with liver cancer, acute toxicosis, and growth impairment in humans and animals. In India, sunflower seeds are a source of snacks, cooking oil, and animal feed. These seeds are a potential source of aflatoxin contamination. However, reports on aflatoxin contamination in sunflower seeds and cakes are scarce. The objective of the current study was to determine the potential of Aspergillus flavus and total aflatoxin concentrations in sunflower seeds and cakes from small-scale oil processors in Rohilkhand region of Uttar Pradesh. 126 cultures of Aspergillus flavus were obtained from sunflower kernels, which showed wide variation in their cultural characters. Colour of conidial heads being a stable character was used to divide them into four groups out of which two representative isolates each, based on minimum and maximum number of sclerotia cm-2 of the culture medium were selected. Aflatoxin production by an isolate had positive correlation with the sclerotia production. These results can help in identifying the potent of A. flavus isolates for aflatoxin production and developing proper management strategies. In summary, humans and animals are potentially at high risk of exposure to aflatoxins through sunflower seeds and cakes from micro-scale millers in India and location influences risk.

Iron oxide nanoparticles immobilized Aspergillus flavus manganese peroxidase with improved biocatalytic, kinetic, thermodynamic, and dye degradation potentialities

Manganese peroxidase (MnP) has gained significant attention for treating textile waste due to its ability to oxidize and detoxify a wide range of recalcitrant xenobiotics, including synthetic dyes. MnP was isolated from a solid-state culture of Aspergillus flavus using pre-optimized conditions of 5 g wheat bran (66% moisture content), pH 4.5, temperature 30 ℃, carbon source: glucose 2%, nitrogen source: yeast extract 0.02%, 5 ml of homogenous fungal spore suspension and fermentation period of 5 days. The extracted MnP was partially purified using ammonium sulfate precipitation and immobilized on iron oxide nanoparticles. Soluble and immobilized MnP showed the maximum catalytic potential at 35 ℃ and 50 ℃, and optimum pH of 4.0 and 5.0, respectively. Vmax and Km for free MnP were 0.126 U/mg and 0.0886 mM, and 0.140 U/mg and 0.704 mM for the immobilized MnP, respectively. Thermodynamic parameters, including Ea, ΔH*, ΔG*, ΔS* were also investigated for free and immobilized MnP. Finally, the soluble and immobilized MnP were exploited for catalytic degradation of two textile dye pollutants, Direct red 31 and Acid black 234. Free MnP catalyzed 94% decolorization of Direct red 31, while 100% decolorization was achieved with immobilized MnP. On the other hand, Acid black 234 showed 85% and 92% decolorization with free and immobilized MnP, respectively. The magnetically separable immobilized MnP was more thermally stable, can work over a wider pH and temperature range, and be more catalytically vigorous than its free counterpart.

STUDYING THE INFLUENCE OF PLASMA-CHEMICAL AND OZONE TREATMENT ON ARTIFICIALLY IMPLEMENTED MICROFLORA IN MODEL AQUEOUS SOLUTIONS

The pilot studies have been conducted to determine the biocidal effects of ozone and plasma chemical treatment for 1, 2, and 3 h on the strain “Moldavian” of infectious rhinotracheitis virus, reference strain of Escherichia coli ATCC 25922, atypical mycobacteria of the species Mycobacusleum phlei and archival strain of Aspergillus flavus artificially introduced into aqueous solution. It is shown that both treatments of aqueous solution contaminated with infectious rhinotracheitis virus have virucidal properties at the level of 95…100%. It was found that bactericidal (bacteriostatic) effect of ozone treatment for Escherichia coli fluid was 100% for all the time parameters. For plasma chemical treatment, the bacteriostatic effect (23%) was shown after the treatment within 3 h. The bactericidal (bacteriostatic) effect of ozone treatment for water samples contaminated with mycobacteria of the species M. phlei was only 65% at the treatment for 3 h. There was no bacteriostatic effect for plasma chemical treatment at any exposure. When studying the fungicidal (fungistatic) properties of ozone treatment for aqueous solution contaminated with a test culture of Aspergillus flavus, fungicidal properties were established (growth retardation by 95…98%). No fungicidal or fungistatic properties were shown for plasma chemical treatment.

Effect of African nutmeg (Monodora myristica) spice in aflatoxin-infected diets on growth performance of broilers

Fungal infected feedstuffs are denatured in nutrients and cause them to develop off flavors that often dampen the appetite of livestock and poultry. In this study, the effect of toasted African nutmeg (Monodora myristica) spice in Aspergillus flavus-infested diets on growth performance of broilers was investigated in a 2 x 3 factorial experimentthat lasted for 42 days. Three out of 6 dietary treatments were infected with 1mg of pure culture of Aspergillus flavus and toasted Monodora myristica spice included at 0%, 0.5% and 1.0% while the other 3 diets were infection-free with 0%, 0.5% and 1.0% Monodora myristica inclusion respectively. Each treatment was replicated three times at 30 chickens per replicate. Infection status was significant (P<0.05) for daily weight gain, feed conversion ratio (FCR) and protein efficiency ratio (PER). Daily weight gain, feed conversion ratio and protein efficiency ratio were 134.19g/bird/day, 39.23g/bird/day, 3.59g/bird/day and 1.10g/bird/day, respectively for the non-infected diets. The aflatoxin infection from Aspergillus flavus was observed to reduce (P<0.05) feed intake to 130.51g/bird/day and weight gain (33.67g/bird/day). FCR and PER were also reduced (P<0.05) by the presence of aflatoxin from Aspergillus flavus in the diet. Effect of Monodora myristica supplementation on feed intake, average daily weight gain, FCR and Protein efficiency ratio was significant (P<0.05) for all the measured parameters. The Feed intake, average daily weight gain, FCR and protein efficiency increased (P<0.05) as Monodora myristica inclusion level increased. Feed intake (119.8g/b/d), daily weight gain (28.90g/b/d), FCR (4.28) and PER (0.94) were observed in the Monodora-free (0%) diet. 0.5% and 1.0% levels of Monodora inclusion produced similar (P>0.05) effects on all the growth parameters but were higher than the control. The interaction of aflatoxin infection and Monodora inclusion level were significant for all the growth parameters. The interaction of aflatoxin infection x Monodora inclusion levels recorded feed intake of 107.97g/b/d, 137.36 and 146.19g/b/d respectively for 0, 0.5 and 1.0% Monodora; 22.27g/b/d, 37.87g/b/d and 40.83g/b/d daily weight gain and 4.85%, 3.63% and 3.58% FCR. The interaction effect of Monodora inclusion level in infection-free diets on the birds feed intake were 131.65g/b/d, 147.24g/b/d and 123.67g/b/d respectively for 0%, 0.5% and 1.0%. The interaction effect at 0.5% inclusion level x non-infected diet was significantly higher (41.31g/b/d) than that at 0% inclusion level on daily gain. However, the daily weight gain of 40.83g/b/d observed in the interaction of 1.0% Monodora level x aflatoxin -free diet similar (P<0.05) to that observed in the 0.5% inclusion level. The feed conversion ratio produced by the interactions at the three different levels (0, 0.5 and 1.0%) in the Aspergillus-free diets were (P>0.05) 3.71, 3.57 and 3.49 respectively while PER were (P<0.05) 1.05, 1.13 and 1.11 respectively. The Monodorafree diet recorded 9.26% drumstick, 2.26% liver 0.65% kidney and 2.43% gizzard, while the diet that had 0.5% Monodora myristica yielded 2.12% liver and 2.29% gizzard. Inclusion of Monodora up to 1.0% recorded 1.63% liver weight. Aspergillus flavus alone caused a reduction in live weight, dressed weight, thigh, kidney, breast meat, gizzard and an enlargement in the liver. Monodora myristica inclusion level also affected (p<0.05) all the parameters except dressed weight, thigh and back cut. Kidney and liver were observed to decrease as the level of inclusion of Monodora myristica increased. The interaction of Monodora myristica and Aspergillus flavus on the parameters were significant (p<0.05). From the results, Monodora myristica may be beneficial to poultry farmers, since about 90% of the poultry feed ingredients especially grains are constantly exposed to aflatoxin infection from Aspergillus flavus and other mycotoxin infections which hinder maximum nutrient utilization and affect the rate of conversion of feed.

High voltage atmospheric cold plasma treatment inactivates Aspergillus flavus spores and deoxynivalenol toxin

Fungal contamination is a concern for the food industry. Fungal spores resist food sterilization treatments and produce mycotoxins that are toxic for animals and humans. Technologies that deactivate spores and toxins without impacting food quality are desirable. This study demonstrates the efficiency of a high voltage atmospheric cold plasma (HVACP) technology using air to generate reactive oxygen (ROS) and nitrogen (RNS) species for the degradation of Aspergillus flavus cultures and the deoxynivalenol (DON) mycotoxin. Optical emission and absorption spectroscopy demonstrate ionization of hydroxyl groups, atomic oxygen and nitrogen, and confirm production of ROS and RNS, e.g. O3, NO2, NO3, N2O4, and N2O5. Fungal cultures show a depletion in pigmentation and an ~50% spore inactivation after 1-min treatments. Treated spores show surface ablation and membrane degradation by scanning electron microscopy. Twenty-minute direct HVACP treatments of 100 μg of DON in one mL aqueous suspensions resulted in a greater than 99% reduction in DON structure and rescued over 80% of Caco-2 cell viability; however, the same treatment on 100 μg of powdered DON toxin only showed a 33% reduction in DON and only rescued 15% of cell viability. In summary, HVACP air treatment can inactivate both fungal spores and toxins in minutes.

Isolation and identification of toxigenic fungi from infected peanuts and efficacy of silver nanoparticles against them

Peanuts are vulnerable to fungal infections during long term storage. Fungi infecting peanuts are toxigenic and cause health hazards. The goal of this study was isolation and identification of fungi in peanuts and use of silver nanoparticles (AgNPs) to inhibit them. For this purpose firstly, we have isolated fungi from infected peanuts and identified on the basis of morphological and molecular study. Out of the total 54 fungal isolates, 47 were found to be Aspergillus spp. and other belongs to Penicillium spp. and Macrophomina phaseolina. Biochemical assay was performed to identify cultures of Aspergillus flavus from other species of this genus by inoculating it on Aspergillus Differentiation Medium (ADM). Thirty-one isolates were found to be A. flavus. Toxicity of Aspergillus spp. was evaluated on Yeast Extract Sucrose agar (YES) medium with an additive methylated β-cyclodextrin and nine isolates were found toxigenic. Secondly, AgNPs were synthesized from ten different plants and their characterization was performed using various analytical techniques such as UV–Visible spectrophotometer, Fourier Transform Infrared Spectroscopy, Zetasizer and Nanoparticle Tracking Analysis, etc. Further, antifungal potential of thus synthesized AgNPs was evaluated. All the synthesized AgNPs possess ability to inhibit fungal growth. Cymbopogon citratus leaf extract mediated AgNPs were found to have prominent antifungal potential against all test fungi and its minimum inhibitory concentration (MIC) was found to be 20 μg/ml. The biogenic approach proposed in the present study is eco-friendly, safe and economical viable. AgNPs also reported to have significant antifungal activity against toxigenic isolates of peanuts, hence such AgNPs can be effectively used for the management of toxigenic pathogens.

Application of loop-mediated isothermal amplification assays for direct identification of pure cultures of Aspergillus flavus, A. nomius, and A. caelatus and for their rapid detection in shelled Brazil nuts

Brazil nuts have a high nutritional content and are a very important trade commodity for some Latin American countries. Aflatoxins are carcinogenic fungal secondary metabolites. In Brazil nuts they are produced predominantly by Aspergillus (A.) nomius and A. flavus. In the present study we applied and evaluated two sets of primers previously published for the specific detection of the two species using loop-mediated isothermal amplification (LAMP) technology. Moreover, a primer set specific for A. caelatus as a frequently occurring non-aflatoxigenic member of Aspergillus section Flavi in Brazil nuts was newly developed. LAMP assays were combined with a simplified DNA release method and used for rapid identification of pure cultures and rapid detection of A. nomius and A. flavus from samples of shelled Brazil nuts. An analysis of pure cultures of 68 isolates representing the major Aspergillus species occurring on Brazil nuts showed that the three LAMP assays had individual accuracies of 61.5%, 84.4%, and 93.3% for A. flavus, A. nomius, and A. caelatus, respectively when morphological identification was used as a reference. The detection limits for conidia added directly to the individual LAMP reactions were found to be 105 conidia per reaction with the primer set ID9 for A. nomius and 104 conidia per reaction with the primer set ID58 for A. flavus. Sensitivity was increased to 101 and 102 conidia per reaction for A. nomius and A. flavus, respectively, when sample preparation included a spore disruption step. The results of LAMP assays obtained during the analysis of 32 Brazil nut samples from different regions of Brazil and from different steps in the production process of the commodity were compared with results obtained from mycological analysis and aflatoxin analysis of corresponding samples. Compared with mycological analysis of the samples, the Negative Predictive Values of LAMP assays were 42.1% and 12.5% while the Positive Predictive Values were 61.5% and 66.7% for A. nomius and A. flavus, respectively. When LAMP results were compared with the presence of aflatoxins in corresponding samples, the Negative Predictive Values were 22.2% and 44.4% and the Positive Predictive Values were 52.2% and 78.3% for aflatoxins produced by A. nomius and A. flavus, respectively. The LAMP assays described in this study have been demonstrated to be a specific, sensitive and easy to use tool for the survey of Brazil nuts for contaminations with potential aflatoxin-producing A. nomius and A. flavus in low tech environments where resources may be limited.

Partial Purification of Amylase from the Culture Filtrates of Aspergillus flavus Grown on Cassava Peels

Amylase from a Cassava peel culture of Aspergillus flavus was partially purified by Ammonium Sulphate precipitation as well as dialysis. The dialysed 60% (NH4)2 SO4 precipitated enzyme had an activity of 1.087 mg T.R.S released/ min/mg protein which was two folds of the activity of the crude culture filtrate. Hydrogen ion concentration as well as temperature had profound influence on enzyme activity of the partially purified enzyme while Amylase activity increased progressively as pH was increased from 3 to 7 reaching a maximum of 1.68 mg T.R.S released/min/mg/protein at PH 7.0. A rapid decrease in amylase activity was observed as pH was increased from 7 to 9 while the amylase activity increased with increase in temperature from 300C to 450C and reached a maximum of 1.15 mg T.R.S. released/min/mg/protein at 450C. Subsequent increase in temperature resulted into decrease in activity of the amylase enzyme.

Factors associated with the incidence of Aspergillus section Flavi and aflatoxin contamination of peanuts in the Busia and Homa bay districts of western Kenya

The aim of this study was to identify agronomic, ecological and sociocultural factors that could be modified to reduce the risk of aflatoxin contamination of peanuts from western Kenya. Presence of fungi within section Flavi of the genus Aspergillus and levels of total aflatoxin were determined for 436 peanut samples from the Busia and Homa bay districts. A total of 1458 cultures of Aspergillus flavus or A. parasiticus isolated from the samples were assayed for production of aflatoxin B1, B2, G1 and G2. Associations among the incidences of fungal species, incidences of samples with ≥10 μg kg−1 aflatoxin, production of specific aflatoxin types and various agronomic, ecological and sociocultural factors were modelled with chi‐squared and logistic regression methods. The predominant species were A. flavus L‐strain (78% incidence), A. flavus S‐strain (68%) and A. niger (65%). Occurrence of A. caelatus, A. alliaceus and A. tamarii in Kenya was also documented. Samples from the Busia district were three times (odds ratio = 3·01) as likely to contain ≥10 μg kg−1 of total aflatoxin as were samples from the Homa bay district, while samples containing A. flavus S‐strain were 96% more likely to exceed this threshold compared with samples from which this fungus was not isolated. Grading, planting improved cultivars and membership of a producer marketing group were negatively associated with the incidence of A. flavus, while crop rotation was negatively correlated with the incidence of B aflatoxins. These sociocultural factors can be modified to reduce the risk of peanut contamination with aflatoxin.

Present and future directions of translational research on aflatoxin and hepatocellular carcinoma. A review

The aflatoxins were discovered in toxic peanut meal causing “turkey X” disease, which killed large numbers of turkey poults, ducklings and chicks in the UK in the early 1960s. Extracts of toxic feed induced the symptoms in experimental animals, and purified metabolites with properties identical to aflatoxins B1 and G1 (AFB1 and AFG1) were isolated from Aspergillus flavus cultures. Structure elucidation of aflatoxin B1 was accomplished and confirmed by total synthesis in 1963. AFB1 is a potent liver carcinogen in rodents, non-human primates, fish and birds, operating through a genotoxic mechanism involving metabolic activation to an epoxide, formation of DNA adducts and, in humans, modification of the p53 gene. Aflatoxins are unique among environmental carcinogens, in that elucidation of their mechanisms of action combined with molecular epidemiology provides a foundation for quantitative risk assessment; extensive evidence confirms that contamination of the food supply by AFB1 puts an exposed population at increased risk of developing hepatocellular carcinoma (HCC). Molecular biomarkers to quantify aflatoxin exposure in individuals were essential to link aflatoxin exposure with liver cancer risk. Biomarkers were validated in populations with high HCC incidence in China and The Gambia, West Africa; urinary AFB1–N 7-Guanine excretion was linearly related to aflatoxin intake, and levels of aflatoxin–serum albumin adducts also reflected aflatoxin intake. Two major cohort studies employing aflatoxin biomarkers identified their causative role in HCC etiology. Results of a study in Shanghai men strongly support a causal relationship between HCC risk and the presence of biomarkers for aflatoxin and HBV infection, and also show that the two risk factors act synergistically. Subsequent cohort studies in Taiwan confirm these results. IARC classified aflatoxin as a Group 1 human carcinogen in 1993, based on sufficient evidence in humans and experimental animals indicating the carcinogenicity of naturally occurring mixtures of aflatoxins, aflatoxin B1, G1 and M1. Aflatoxin biomarkers have also been used to show that primary prevention to reduce aflatoxin exposure can be achieved by low-technology approaches at the subsistence farm level in sub-Saharan Africa. Also, in residents of Qidong, China, oral dosing with chlorophyllin, a chlorophyll derivative, prior to each meal led to significant reduction in aflatoxin–DNA biomarker excretion, supporting the feasibility of preventive measures to reduce HCC risk in populations experiencing unavoidable aflatoxin exposure. The systematic, comprehensive approach used to create the total aflatoxin database justifies optimism for potential success of preventive interventions to ameliorate cancer risk attributable to aflatoxin exposure. This strategy could serve as a template for the development, validation and application of molecular and biochemical markers for other carcinogens and cancers as well as other chronic diseases resulting from environmental exposures.

Steroids and an oxylipin from an algicolous isolate of Aspergillus flavus

A new oxylipin, (8E,12Z)-10,11-dihydroxyoctadeca-8,12-dienoic acid (1), a new steroid, 3β,4α-dihydroxy-26-methoxyergosta-7,24(28)-dien-6-one (2), and four known steroids, episterol (3), (22E,24R)-ergosta-7,22-dien-3β,5α,6α-triol (4), (22E,24R)-ergosta-5,22-dien-3β-ol (5), and (22E,24R)-ergosta-4,6,8(14),22-tetraen-3-one (6), were isolated from the cultures of Aspergillus flavus, an endophytic fungus isolated from the marine red alga Corallina officinalis. Their structures and relative stereochemistry were elucidated by 1D, 2D NMR and mass spectroscopic techniques. 1 and 2 exhibited low activity to inhibit acetylcholinesterase and no activity against plant pathogenic fungi Colletotrichum lagenarium and Fusarium oxysporum.

Fluorescent Viability Stains to Probe the Metabolic Status of Aflatoxigenic Fungus in Dual Culture of Aspergillus flavus and Pichia anomala

The metabolic activity of the aflatoxigenic fungus, Aspergillus flavus co-cultured with the biocontrol yeast, Pichia anomala was examined using several viability stains. Both the FUN-1 stain and the combined use of DiBAC(4)(5) with CDFA-AM stains were applied in this study. The results suggest that the ATP-generating system in A. flavus was inactivated as the ratio of yeasts to fungi increased in the dual culture. A decrease in hyphal membrane potential and esterase activity was substantiated by the combined stains of DiBAC(4)(5) and CDFA-AM. Reduced metabolic function in conjunction with cell wall damage of A. flavus hindered the growth and biomass production of this fungus. Viability stains such as FUN-1 and DiBAC(4)(5) with CDFA-AM may assist in elucidating the biocontrol mechanism by allowing for the visualization of the antagonistic effect of yeast species on target fungi in situ, as well as for screening potent biocontrol yeast agents against fungal pathogens.

Absence of the aflatoxin biosynthesis gene, norA, allows accumulation of deoxyaflatoxin B1 in Aspergillus flavus cultures

Biosynthesis of the highly toxic and carcinogenic aflatoxins in select Aspergillus species from the common intermediate O-methylsterigmatocystin has been postulated to require only the cytochrome P450 monooxygenase, OrdA (AflQ). We now provide evidence that the aryl alcohol dehydrogenase NorA (AflE) encoded by the aflatoxin biosynthetic gene cluster in Aspergillus flavus affects the accumulation of aflatoxins in the final steps of aflatoxin biosynthesis. Mutants with inactive norA produced reduced quantities of aflatoxin B(1) (AFB(1)), but elevated quantities of a new metabolite, deoxyAFB(1). To explain this result, we suggest that, in the absence of NorA, the AFB(1) reduction product, aflatoxicol, is produced and is readily dehydrated to deoxyAFB(1) in the acidic medium, enabling us to observe this otherwise minor toxin produced in wild-type A. flavus.

Disinfection of selected Aspergillus spp. using ultraviolet germicidal irradiation.

The efficacy of ultraviolet germicidal irradiation (UVGI) and the UVGI dose necessary to inactivate fungal spores on an agar surface for cultures of Aspergillus flavus and Aspergillus fumigatus were determined. A four-chambered UVGI testing unit with a 9-W, Phillips, low pressure, mercury UVGI lamp in each chamber was used in this study. An aperture was adjusted to provide 50, 100, 150, and 200 micro W/cm2 of uniform flux to the surfaces of the Petri dish, resulting in a total UVGI dose to the surface of the Petri dishes ranging from 12 to 96 mJ/cm2. The UVGI dose necessary to inactivate 90% of the A. flavus and A. fumigatus was 35 and 54 mJ/cm2, respectively. UVGI can be used to inactivate culturable fungal spores. Aspergillus flavus was more susceptible than A. fumigatus to UVGI. These results may not be directly correlated to the effect of UVGI on airborne fungal spores, but they indicate that current technology may not be efficacious as a supplement to ventilation unless it can provide higher doses of UVGI to kill spores traveling through the irradiated zone.

Degradation of metolachlor in soil inoculated with a mixed fungal culture

The effect of a mixed fungal culture on the degradation of the herbicide metolachlor in soil was evaluated. Metolachlor was found to degrade up to 92% and 87% after 20 days in sterile and nonsterile soils respectively, when inoculated with a mixed culture of Aspergillus flavus and Aspergillus terricola and treated with 20 μg g–1 metolachlor. When the soil was treated at 50 μg g–1 level, 84% of the added herbicide degraded in inoculated sterile soil and 80% in nonsterile soil. The half-lives of metolachlor were found to be 5 and 4 times faster at the 20 and 50 μg g–1 levels, respectively, in the presence of the mixed fungal culture. In treated soils, four metabolites could be identified by RP-HPLC.

Characteristics of collagenolytic enzymes secreted by deuteromycete fungi Aspergillus flavus.

Collagen induced the synthesis of collagenolytic enzymes in the culture of Aspergillus flavus. Enzyme activity of the culture increased during storage and passage on a medium with this inductor. We developed a method for isolation and purification of collagenolytic enzymes and obtained two electrophoretically homogenous enzyme preparations belonging to neutral thermolabile collagenolytic metalloproteinases.

Biflavonoids inhibit the production of aflatoxin by Aspergillus flavus.

The biflavonoids 6,6"-bigenkwanin, amenthoflavone, 7,7"-dimethoxyagastisflavone and tetradimethoxybigenkwanin isolated from Ouratea species were tested for inhibitory activity on Aspergillus flavus cultures. Suspensions of Aspergillus flavus spores were inoculated into 50 ml of YES medium at different biflavonoid concentrations: 5 and 10 microg/ml for 6,6"-bigenkwanin, amenthoflavone and 7,7"-dimethoxyagastisflavone, and 5, 10, 15 and 20 microg/ml for tetradimethoxybigenkwanin. The four biflavonoids showed inhibitory activity on aflatoxin B1 and B2 production (P<0.001), but did not inhibit fungal growth at the concentration tested (P>0.05). These results show that biflavonoids can be used for the development of agents to control aflatoxin production.

Identification and effects of maize silk volatiles on cultures of Aspergillus flavus.

Volatiles generated from corn silks of individual genotypes of maize were found to exhibit differences in biological activities when the volatiles were exposed to 5-day solid cultures of Aspergillus flavus. In inverted potato dextrose-agar Petri plate bioassays, it was found that volatiles emitted from silks of the different maize genotypes had a profound effect on the growth of the fungus and, consequently, aflatoxin production. To determine the underlying cause for this bioactivity, volatiles emitted from the maize silks were trapped on Tenax glass columns and were analyzed by GC-MS. Aflatoxin field-resistant maize genotypes exhibited a larger relative concentration of the antifungal aldehyde, furfural (2-furancarboxaldehyde), when compared to the relative concentrations of the field-susceptible varieties tested. In a closed-container 5-day study, it was observed that fresh 1- and 4-day-old corn silk samples of aflatoxin-resistant maize genotypes emitted higher concentrations of furfural compared to those from susceptible genotypes. This observation probably explains the reason for the bioactivity observed in the in vitro bioassays, and the presence of furfural appears to contribute to a defense mechanism for protecting the developing maize kernel from fungal attack.

Aflatoxin B1 and fumosin B1 in mixed cultures of Aspergillus flavus and Fusarium proliferatum on maize.

Production of aflatoxin B1 and fumonisin B1 in pure and mixed cultures of Aspergillus flavus and Fusarium proliferatum were determined on irradiated maize seeds inoculated with different spore concentrations at 0.97 water activity (a(w)) and a temperature of 25 degrees C. The highest levels of aflatoxin B1 were produced by A. flavus at the lowest levels of inoculum (10(3) spore ml(-1)). There was no spore concentration influence on fumonisin B1 production after 10, 20 and 35 days of incubation. When A. flavus was co-inoculated with F. proliferatum, aflatoxin B1 production was inhibited. The higher the inocula levels of Fusarium produced, the higher the inhibition and this inhibition increased during the incubation period. Total inhibition was reached at 35 days of incubation. There was no interaction influence on fumonisin B1 production at all inoculum levels assayed. These results suggest that under optimal environmental conditions of substrate, water activity and temperature, the interaction between A. flavus and F proliferatum could produce inhibition of aflatoxin B1 and stimulation of fumonisin B1.