Mechanism of inhibition of aflatoxin synthesis by non-aflatoxigenic strains of Aspergillus flavus.

Aflatoxins are toxic secondary metabolites primarily produced by Aspergillus flavus and A. paraciticus. Exposure to these mycotoxins through contaminated food and feed may cause oxidative stress and liver toxicity in animals. One of the promising strategies to mitigate aflatoxin accumulation is the biological management during pre-harvest using non-aflatoxigenic A. flavus. The mechanism offered by these strains in mitigating aflatoxin is still unclear. Thus, the aim of the present study is to delineate the mechanism of intraspecific inhibition of aflatoxin production. Among the 18 non-aflatoxigenic strains evaluated, six strains were able to reduce more than 50% of the aflatoxins produced by the native aflatoxigenic strains. The non-aflatoxigenic strains used in this study failed to degrade the aflatoxins. Eventhough, the non-aflatoxigenic strains were not able to inhibit the synthesis of aflatoxins completely. Four non-aflatoxigenic isolates could competitively excluded the aflatoxigenic strain. Furthermore, when non-aflatoxigenic and an aflatoxigenic isolate were separated by 0.4 and 3 μm filters, aflatoxin synthesis was not significantly reduced. However, when the pore size was 8 μm, there was a significant decrease in aflatoxin production. This results suggest the role of physical contact between the hyphae, thigmoregulation, in the inhibition of aflatoxin production. Additionally, to better understand the transcriptional level control of this phenomenon, we analyzed the gene expression profile of aflatoxin biosynthesis genes in the aflatoxigenic strain. The aflatoxin biosynthesis genes were down regulated in the aflatoxigenic strain in contact with non-aflatoxigenic strain group when compared to the control. This is the first evidence of the combined action of competitive exclusion and thigmodownregulation which led to the intraspecific inhibition of aflatoxin production.