Figure 1.

Precursor and terminal metabolites in AF biosynthesis. Sterigmatocystin (ST), O-methylsterigmatocystin (OMST) and aflatoxins (AF) are synthesized as end products by numerous ascomycetes. There are four major aflatoxins: B₁, B₂, G₁ and G₂. Aflatoxins B₂ and G₂ are missing the double bond (indicated in red), which is present in B₁ and G₁. A. parasiticus produces B₁, B₂, G₁ and G₂; nonaflatoxigenic A. parasiticus strains commonly accumulate OMST. The gene aflU is required for the formation of G aflatoxins [10]; aflQ is required for the formation of B aflatoxins [17]; and aflP is required for the conversion of ST to OMST [17]. A. flavus, A. parasiticus, A. nomius [68], A. pseudotamarii [69] and A. bombycis [68] belong to Aspergillus section Flavi. Emericella is a teleomorphic genus for the sexual stage of Aspergillus. Monocillium is an anamorphic name associated with a Niesslia teleomorph, also in the Phylum Ascomycota. The Ascomycota comprise highly divergent fungal lineages that span 450 million years of evolutionary history [70].