| In recent years,the harmful effects of fungi and their toxins on humans and animals have become more and more serious,mainly through the direct pollution of agricultural and sideline products,which indirectly threaten the health and safety of humans and animals.Fungal diseases are also common among humans and animals.Aspergillus flavus is a fungus belonging to the genus Aspergillus.It is mainly transmitted through the production of conidia.It can contaminate many important agricultural and sideline products and poses a threat to the health of humans and animals.Aflatoxin is a toxic,mutagenic,carcinogenic and teratogenic secondary metabolite that poses health hazards to humans and animals.The emerging prevention and control technologies for Aspergillus flavus and its toxins are based on biological control.Therefore,74 strains of laboratory-preserved strains in this study were screened and rescreened to screen a strain that significantly inhibits the growth of Aspergillus flavus.Strain B10,which was optimized for its culture conditions,was crudely extracted from its aseptic supernatant and studied the antibacterial mechanism of its crude extract,and studied the expression levels of several key toxin-producing genes of Aspergillus flavus in crude extract of B10.The impact of this study lays a theoretical and practical foundation for the prevention and control of aflatoxin in humans and animals using biological control technologies.The main test results are as follows:(1)Determine the antagonistic bacteria that can inhibit the growth of Aspergillus flavus as Bacillus amyloliquefaciens by biochemical identification,routine identification,and molecular biological identification.(2)Conditioning culture of antagonistic bacteria was optimized.The inhibition rate of the culture supernatant to Aspergillus flavus was used as a measure to determine the optimal conditions for culture conditions of antagonistic bacteria: temperature 40°C,incubation time 36 h,inoculum size 3%,speed 120 r/min,pH 6,liquid volume 30 ml.(3)Crude extracts of the aseptic supernatant of antagonistic bacteria B10 were obtained to obtain crude extracts of antibacterial active substances,and the properties of the extracts were studied.The crude extracts were found to inhibit the growth of Aspergillus flavus significantly by the plate counterbalancing method.Antibacterial zone.The crude extracts of antibacterial substances were added to PDA(potato-dextrose agar medium)in different amounts and co-cultured with Aspergillus flavus,and it was found that the weight of mycelium decreased significantly with the increase of crude extracts.After mycelium staining and microscopic examination,compared with normal mycelia,the shape of mycelia after treatment with the crude extract of antibacterial substances was obviously distorted and atrophied,indicating that the crude extract of antibacterial substances had the effect on the growth of mycelium.Inhibition and destructive effects.(4)The crude extracts of antibacterial substances were added to PDA and cultured in different amounts.The expression of Aspergillus flavus toxigenic genes was detected by fluorescence quantitative PCR.The results were compared with that of the group A without crude extract: Aspergillus flavus production.The transcription levels of the aflR and aflK genes gradually decreased with the increase of the amount of crude extract(P<0.05),and the transcription level of aflQ gene increased with the increase of crude extracts(P<0.05).Conclusion: The antagonistic bacteria screened out in this study were identified as Bacillus amyloliquefaciens.The crude extract of antibacterial substances can significantly inhibit the growth of Aspergillus flavus mycelium and destroy its morphology,and inhibit the key genes aflR and aflK producing Aspergillus flavus.expression. |
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