Aflatoxin B1 inhibition in Aspergillus flavus by Aspergillus niger through down-regulating expression of major biosynthetic genes and AFB1 degradation by atoxigenic A. flavus.

Twenty Aspergillus niger strains were isolated from peanuts and 14 strains were able to completely inhibit AFB1 production with co-cultivation. By using a Spin-X centrifuge system, it was confirmed that there are some soluble signal molecules or antibiotics involved in the inhibition by A. niger, although they are absent during the initial 24h of A. flavus growth when it is sensitive to inhibition. In A. flavus, 19 of 20 aflatoxin biosynthetic genes were down-regulated by A. niger. Importantly, the expression of aflS was significantly down-regulated, resulting in a reduction of AflS/AflR ratio. The results suggest that A. niger could directly inhibit AFB1 biosynthesis through reducing the abundance of aflS to aflR mRNAs. Interestingly, atoxigenic A. flavus JZ2 and GZ15 effectively degrade AFB1. Two new metabolites were identified and the key toxic lactone and furofuran rings both were destroyed and hydrogenated, meaning that lactonase and reductase might be involved in the degradation process.