Research On The Combined Use Of Biofertilizer And Chemical Fertilizer For Aflatoxin Prevention

Afatoxin is a secondary metabolite produced by Aspergillus.It has strong carcinogenic and mutagenic effects,and is not easy to decompose.The effect of traditional removal methods is unstable,which seriously threatens food safety and human health.The use of biological control can prevent aflatoxin contamination from the source.At present,the main biological control method of aflatoxin is to use non-toxin-producing Aspergillus flavus to antagonize toxin-producing Aspergillus flavus.However,due to the inherent diversity and genetic complexity of Aspergillus species,non-toxin-producing Aspergillus flavus may undergo genetic mutation to transform into toxin-producing strains.Therefore,the large-scale use of non-toxin-producing Aspergillus flavus is a potential threat in the long run.Due to the long-term application of chemical fertilizer,soil structure is destroyed,organic matter content decreases,soil acidification,salinization and other problems become more and more prominent.Relevant experts suggest that increasing soil beneficial microorganisms play an important role in improving soil structure,improving soil fertility,and improving crop yield and quality.In this study,the effect and feasibility of Aspergillus oryzae as a biocontrol strain of aflatoxin were discussed from the two aspects of inhibiting the growth and reproduction of Aspergillus flavus and inhibiting the toxicity.Both Aspergillus oryzae and Aspergillus flavus belong to Genus Aspergillus,and they have similar morphology and similar genomes.In this study,Aspergillus oryzae,Bacillus mucilaginosus,inorganic nutrients and organic nutrients were combined with microbial immobilization technology to prepare a compound microbial fertilizer which could not only control aflatoxin pollution by biological prevention and control technology,but also improve soil quality.The main research contents are as follows:（1）Explores the aspergillus oryzae on solid medium and liquid medium for the antagonism between produce poison aflatoxin.The experiment found 3 strains of Aspergillus oryzae（AO380）,Aspergillus oryzae（AO382）,and Aspergillus oryzae（AO936）with different functions.There is no significant difference between their inhibitory effects on the growth and reproduction of toxin-producing Aspergillus flavus（WY-4）and the inhibitory effect of the non-toxin-producing Aspergillus flavus（H-2）on the toxin-producing Aspergillus flavus（WY-4）screened in the previous laboratory.The inhibition rate of the three strains of Aspergillus oryzae on the growth of the toxin-producing Aspergillus flavus was 46.05%～47.37%,and that of the non-toxin-producing Aspergillus flavus was 46.95%.Three strains of Aspergillus oryzae and Aspergillus flavus were inoculated on soybean medium for mixed culture.It was found that all three strains of Aspergillus oryzae could inhibit the production of toxins by Aspergillus flavus,and Aspergillus oryzae could be used as candidate strains for biological control of aflatoxin.（2）The effects of different concentrations of urea and KH₂PO₄ on the growth and reproduction of Aspergillus oryzae and Bacillus gelatinus were investigated by using liquid medium containing different concentrations of urea and KH₂PO₄.The number of Aspergillus oryzae decreased seriously when the concentration of urea in the medium reached 3%.KH₂PO₄ concentration in the medium in the range of 0%～4%can promote the growth of Aspergillus oryzae.When the concentration is more than 4%,the effect begins to decrease.When the concentration of urea in the medium was greater than 4%,the number of Bacillus gelliform decreased sharply.When the concentration of KH₂PO₄ in the medium exceeds 1%,the damage to Bacillus gelatinus is greater.（3）Composite microbial fertilizer microspheres were prepared by microbial immobilization technology.The mechanical strength,mass transfer performance and embedding rate of the immobilized microspheres were taken as main indexes.At the same time,the effects of six single factors,including SA concentration,Ca Cl₂ concentration,starch concentration,molasses concentration,bacterial suspension concentration and immobilization time,on the preparation of immobilized microspheres were analyzed.On the basis of single factor experiments,the response surface method（RSM）was used to optimize the preparation conditions of the immobilized microspheres,and the optimal ratio of each formulation in the preparation process of the composite microbial fertilizer microsphere particles was obtained.The optimum ratio was as follows:starch concentration 10%（w/v）,SA concentration 1.6%（w/v）,Ca Cl₂ concentration 2%（w/v）,bacteria suspension ratio 10%（w/v）,molasses concentration 2%（w/v）,curing time 1 h.（4）The performance of microspheres was further improved by adding kaolin,straw powder and biochar into the basic formula of microspheres.It was found that the addition of kaolin,straw powder and biochar significantly enhanced the mechanical strength of the immobilized microspheres.The addition of kaolin,straw powder and biochar can significantly reduce the swelling ratio of microspheres,and have a slow-release effect on the release of internal materials of microspheres.The slow-release effect of biochar microspheres is the best,and the addition of biochar can significantly improve the embedding rate of microspheres.The addition of kaolin,straw powder and biochar will reduce the viscoelasticity of the gel microspheres,and also change the microstructure of the microspheres,which is beneficial to the storage of nutrients and the attachment of microorganisms.（5）The practical application effect of the compound microbial fertilizer for biological control was analyzed by pot experiment.The biological control effect of fungal fertilizer on Aspergillus flavus,the improvement effect of soil physical and chemical properties,and the effect on crop yield and quality were investigated.Interaction between Aspergillus oryzae and Bacillus gelatinus after compound microbial fertilizer was applied to soil and the effect of chemical fertilizer on bacteria.The results showed that the application of rice as carrier Aspergillus oryzae to the soil could reduce the number of Aspergillus flavus by43.77%～53.23%,and the biochar fertilizer could reduce the number of Aspergillus flavus by16.82%～27.56%.Compared with the control group,the yield of lettuce increased by 41.32%by applying biochar gelatinoid bacillus compound fertilizer.The effects of Bacillus gelatinus and Aspergillus oryzae on the soil were not regular.Fertilizer can harm the growth and reproduction of Aspergillus oryzae and Bacillus gelatinus,but embedding treatment can reduce the damage.