Step of dichlorvos inhibition in the pathway of aflatoxin biosynthesis

Dichlorvos (dimethyl 2,2-dichlorovinyl phosphate) inhibits the biosynthesis of aflatoxin by Aspergillus parasiticus. Cultures treated with dichlorvos excrete an orange pigment which can be converted into aflatoxin B(1) by the untreated mycelia. The orange pigment was partially identified as an acetyl derivative of versiconol-type compound. In the presence of dichlorvos, sterigmatocystin is converted into aflatoxin B(1) without being interfered, but averufin is converted into the orange pigment instead of aflatoxin B(1). Therefore, dichlorvos appears to block an enzymatic step in the aflatoxin biosynthetic pathway, which lies beyond averufin but before sterigmatocystin, at the formation of the orange pigment.