Molecular Mechanisms Of Atoxigenic Aspergillus Flavus And The Study In Inhibiting The Aflatoxin Production By Toxigenic A.flavus

Aflatoxins are toxic and carcinogenic secondary metabolites mainly produced by Aspergillus flavus andA. parasiticus, and can contaminate many important crops, resulting in serious food and feed safety problemsall over the world and leading to significant economic losses every year. However, there are both atoxigenicA. flavus and A. parasiticus, and studies have shown atoxigenic A. flavus and A. parasiticus can effectivelycontrol the aflatoxins accumulation produced by toxigenic A. flavus and A. parasiticus. Our laboratorydetected some atoxigenic A. flavus from the four agroecological zones(Liaoning, Shandong, Hubei andGuangdong Provinces in China), Amplification the29aflatoxin genes in the aflatoxin gene cluster in theatoxigenic isolates by conventional PCR and detection the key gene expression in atoxigenic A. flavuswithout gene deleted by Real-time PCR to elaborate the molecular mechanisms of atoxigenic A. flavus. Thenthe study analyze the inhibitory effect of the atoxigenic strain on the toxigenic strain, which could provide atheoretical basis and technical support for the prevention of aflatoxin contamination in the field.. The mainconclusions are listed as follows:1. Identified76strains atoxigenic A. flavus from323candidated A. flavus strains islotated from fourpeanut agroecological zones. Then we found that the incidence of atoxigenic A. flavus strains decreasedwith increase in temperature and increased with increase in latitude in different geographical locations.2. Amplification of all the aflatoxin genes in the aflatoxin gene cluster in the atoxigenic isolates showedthat there were25deletion patterns (A-Y).These strains are atoxigenic because of the gene deleted.There are34strains with gene deletion, accounting for44.74%of total atoxigenic A. flavus, indicatingatoxigenic A. flavus strains with gene deletions is not rare. However, the strains from Hubei possessed22deletion patterns, suggesting Hubei has the most varieties of atoxigenic strains which may beassociated with the geographical location and climate.3. Establish a rapid method for detecting atoxigenic A. flavus. Four pairs of genes aflT, nor-1, aflR andhypB were used to efficiently detect atoxigenic A. flavus.The criteria as follows: when the number ofDNA bands were0-3, indicating that the strain was atoxigenic strain; while when the number of DNAbands were4, indicating that the strain was most likely toxigenic A. flavus and needed furtherdetermination.4. Detected the expression levels of9genes in the aflatoxin gene cluster in the atoxigenic isolates byReal-time PCR. The results showed that there has two genes (aflR and nor-1) downregulation rate were100%which suggesting that this42strains are atoxigenic may be closely related to significantreduction in these7gene expression levels.5. Screened six atoxigenic A. flavus could significantly inhibit the aflatoxin production by the strain GZ-1from10isolates with large deletions, AF-1, AF-2, AF-3, AF-4, AF-6and AF-5, respectively. Theatoxigenic A. flavus AF-4could most significantly inhibits more than75.94%aflatoxin production bythe strain GZ-1in peanut and maize kernels. While the atoxigenic A. flavus AF-6could mostsignificantly inhibits more than97.79%aflatoxin production by the strain HB-1in peanut and maize kernels. Whether in peanut or maize medium, atoxigenic A. flavus strains could more efficiently inhibitthe aflatoxin production by HB-1(S-type) than the GZ-1(L-type).