Inhibition of Aflatoxin Production in by a sp. and Its Metabolite Cyclo(l-Ala-Gly).

During an experiment where we were cultivating aflatoxigenic on peanuts, we accidentally discovered that a bacterium adhering to the peanut strongly inhibited aflatoxin (AF) production by . The bacterium, isolated and identified as , was found to produce an AF production inhibitor. Cyclo(l-Ala-Gly), isolated from the bacterial culture supernatant, was the main active component. The aflatoxin production-inhibitory activity of cyclo(l-Ala-Gly) has not been reported. Cyclo(l-Ala-Gly) inhibited AF production in without affecting its fungal growth in a liquid medium with stronger potency than cyclo(l-Ala-l-Pro). Cyclo(l-Ala-Gly) has the strongest AF production-inhibitory activity among known AF production-inhibitory diketopiperazines. Related compounds in which the methyl moiety in cyclo(l-Ala-Gly) is replaced by ethyl, propyl, or isopropyl have shown much stronger activity than cyclo(l-Ala-Gly). Cyclo(l-Ala-Gly) did not inhibit recombinant glutathione--transferase (GST) in , unlike (l-Ala-l-Pro), which showed that the inhibition of GST was not responsible for the AF production-inhibition of cyclo(l-Ala-Gly). When was cultured on peanuts dipped for a short period of time in a dilution series bacterial culture broth, AF production in the peanuts was strongly inhibited, even at a 1 × 10-fold dilution. This strong inhibitory activity suggests that the bacterium is a candidate for an effective biocontrol agent for AF control.