Inhibitory effect of Aspergillus niger on the growth of Aspergillus ochraceus and Aspergillus flavus, and on aflatoxin formation
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Abstract:
Abstract Aspergillus ochraceus and A flavus were grown on synthetic media (SM) supplemented with 50 or 200 ml litre −1 SM on which A niger had been grown previously ( ‘ A niger medium’ = ANM). Controls included SM acidified to pH 6.0 or 4.4, SM diluted with 50 or 200 ml litre −1 water, and diluted‐acidified SM. For both fungi, higher growth inhibition was recorded on ANM‐containing SM than in the controls. Aflatoxin formation was markedly inhibited on SM to which 20 ml litre −1 ANM extract (in methanol/chloroform, 2:1 v) had been added, although the growth of A flavus on that medium was almost the same as that in the control. It is concluded that the inhibitory effect of A niger on the growth of fungi should not be attributed merely to pH reduction, but also, mainly, to metabolites produced by the fungus in the growth medium, even at early stages of its growth.Keywords:
Aspergillus niger
Aspergillus ochraceus
Growth inhibition
Cinnamaldehyde (CA), a natural plant extract, possesses notable antimicrobial properties and the ability to inhibit mycotoxin synthesis. This study investigated the effects of different concentrations of gaseous CA on A. flavus and found that higher concentrations exhibited fungicidal effects, while lower concentrations exerted fungistatic effects. Although all A. flavus strains exhibited similar responses to CA vapor, the degree of response varied among them. Notably, A. flavus strains HN-1, JX-3, JX-4, and HN-8 displayed higher sensitivity. Exposure to CA vapor led to slight damage to A. flavus, induced oxidative stress, and inhibited aflatoxin B1 (AFB1) production. Upon removal of the CA vapor, the damaged A. flavus resumed growth, the oxidative stress weakened, and AFB1 production sharply increased in aflatoxin-producing strains. In the whole process, no aflatoxin was detected in aflatoxin-non-producing A. flavus. Moreover, the qRT-PCR results suggest that the recovery of A. flavus and the subsequent surge of AFB1 content following CA removal were regulated by a drug efflux pump and velvet complex proteins. In summary, these findings emphasize the significance of optimizing the targeted concentrations of antifungal EOs and provide valuable insight for their accurate application.
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The influence of pyridazinone herbicides on aflatoxin production by Aspergillus flavus and A. parasiticus was studied in liquid media. Mycelia production was not affected by 20, 40, or 60 micrograms of herbicide per ml; however, aflatoxin production by A. parasiticus was higher in media with herbicide, whereas A. flavus produced lower aflatoxin levels.
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The population of Aspergillus flavus and the amounts of aflatoxins in maize ears and kernels collected from 4 areas in Thailand in 1987 were studied. Eleven maize ear samples from the randomly selected fields showed no infection of A. flavus and very low amount (9 ppb) of aflatoxin B1 was found in only one sample. Similarly, the infection of A. flavus in 6 maize ear samples collected from farmers' and middlemen's storages was very low (0-3% of kernels from the ear); two samples of them were positive for aflatoxins (aflatoxin B19 and 58 ppb). However, all 15 maize kernel samples collected from the middlemen's storages were found to be highly contaminated with A. flavus and aflatoxins. There were clearly less contaminations of A. flavus and aflatoxins in the maize ear than those in the kernels.
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The efficacies of four different concentrations (3, 5, 8 and 10 mg/ml) of an aqueous extract of the Andrographis peniculata were tested on growth and aflatoxin production by Aspergillus flavus in liquid SMKY medium. The maximum inhibition of aflatoxin production and growth of A. flavus were marked at 10 mg/ml (i.e. 78.6% aft. B1 and 75.1% growth). Growth and aflatoxin production were co-related processes.
Fungal growth
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Two aflatoxin-producing isolates of Aspergillus flavus were grown for 5 days on Wort media at 2, 7, 13, 18, 24, 29, 35, 41, 46, and 52 C. Maximal production of aflatoxins occurred at 24 C. Maximal growth of A. flavus isolates occurred at 29 and 35 C. The ratio of the production of aflatoxin B 1 to aflatoxin G 1 varied with temperature. Aflatoxin production was not related to growth rate of A. flavus ; one isolate at 41 C, at almost maximal growth of A. flavus , produced no aflatoxins. At 5 days, no aflatoxins were produced at temperatures lower than 18 C or higher than 35 C. Color of CHCl 3 extracts appeared to be directly correlated with aflatoxin concentrations. A. flavus isolates grown at 2, 7, and 41 C for 12 weeks produced no aflatoxins. At 13 C, both isolates produced aflatoxins in 3 weeks, and one isolate produced increasing amounts with time. The second isolate produced increasing amounts through 6 weeks, but at 12 weeks smaller amounts of aflatoxins were recovered than at 6 weeks.
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Aspergillus parasiticus
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