Metabolic precursor regulation of aflatoxin formation in toxigenic and non-toxigenic strains of Aspergillus flavus.

Non-aflatoxin-producing isolates of Aspergillus flavus from nature and isolates of A. flavus that had lost their toxigenic trait following laboratory transfer were compared biochemically. After the addition of aflatoxin B1 precursors sterigmatocystin or O-methylsterigmatocystin to whole cell cultures, the non-toxin producing isolates from nature remained non-toxigenic while toxigenicity was restored in the non-toxigenic laboratory strains. Results imply a lack of enzymes needed for biochemical conversions of precursors to aflatoxin B1 in natural non-producers and suppression of these enzymes in the non-producing laboratory strains.