| Summary: | Aflatoxins (AF) are hepatocarcinogenic metabolites produced by several <i>Aspergillus</i> species. Crop infection by these species results in aflatoxin contamination of cereals, nuts, and spices. Etiology of aflatoxin contamination is complicated by mixed infections of multiple species with similar morphology and aflatoxin profiles. The current study investigates variation in aflatoxin production between two morphologically similar species that co-exist in West Africa, <i>A. aflatoxiformans</i> and <i>A. minisclerotigenes</i>. Consistent distinctions in aflatoxin production during liquid fermentation were discovered between these species. The two species produced similar concentrations of AFB<sub>1</sub> in defined media with either urea or ammonium as the sole nitrogen source. However, production of both AFB<sub>1</sub> and AFG<sub>1</sub> were inhibited (<i>p</i> < 0.001) for <i>A. aflatoxiformans</i> in a yeast extract medium with sucrose. Although production of AFG<sub>1</sub> by both species was similar in urea, <i>A. minisclerotigenes</i> produced greater concentrations of AFG<sub>1</sub> in ammonium (<i>p</i> = 0.039). Based on these differences, a reliable and convenient assay for differentiating the two species was designed. This assay will be useful for identifying specific etiologic agents of aflatoxin contamination episodes in West Africa and other regions where the two species are sympatric, especially when phylogenetic analyses based on multiple gene segments are not practical.
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