Taxonomy of<i>Aspergillus</i>section<i>Flavi</i>and their production of aflatoxins, ochratoxins and other mycotoxins

Abstract

Aflatoxins and ochratoxins are among the most important mycotoxins of all and producers of both types of mycotoxins are present in <i>Aspergillus</i> section <i>Flavi</i>, albeit never in the same species. Some of the most efficient producers of aflatoxins and ochratoxins have not been described yet. Using a polyphasic approach combining phenotype, physiology, sequence and extrolite data, we describe here eight new species in section <i>Flavi</i>. Phylogenetically, section <i>Flavi</i> is split in eight clades and the section currently contains 33 species. Two species only produce aflatoxin B₁ and B₂ (<i>A. pseudotamarii</i> and <i>A. togoensis</i>), and 14 species are able to produce aflatoxin B₁, B₂, G₁ and G₂: three newly described species <i>A. aflatoxiformans, A. austwickii</i> and <i>A. cerealis</i> in addition to <i>A. arachidicola</i>, <i>A. minisclerotigenes</i>, <i>A. mottae, A. luteovirescens</i> (formerly <i>A. bombycis</i>)<i>, A. nomius, A. novoparasiticus, A. parasiticus, A. pseudocaelatus, A. pseudonomius, A. sergii</i> and <i>A. transmontanensis</i>. It is generally accepted that <i>A. flavus</i> is unable to produce type G aflatoxins, but here we report on Korean strains that also produce aflatoxin G₁ and G₂. One strain of <i>A. bertholletius</i> can produce the immediate aflatoxin precursor 3-O-methylsterigmatocystin, and one strain of <i>Aspergillus sojae</i> and two strains of <i>Aspergillus alliaceus</i> produced versicolorins. Strains of the domesticated forms of <i>A. flavus</i> and <i>A. parasiticus</i>, <i>A. oryzae</i> and <i>A. sojae</i>, respectively, lost their ability to produce aflatoxins, and from the remaining phylogenetically closely related species (belonging to the <i>A. flavus</i>-, <i>A. tamarii</i>-, <i>A. bertholletius</i>- and <i>A. nomius</i>-clades), only <i>A. caelatus</i>, <i>A. subflavus</i> and <i>A. tamarii</i> are unable to produce aflatoxins. With exception of <i>A. togoensis</i> in the <i>A. coremiiformis</i>-clade, all species in the phylogenetically more distant clades (<i>A. alliaceus</i>-, <i>A. coremiiformis</i>-, <i>A. leporis</i>- and <i>A. avenaceus</i>-clade) are unable to produce aflatoxins. Three out of the four species in the <i>A. alliaceus</i>-clade can produce the mycotoxin ochratoxin A: <i>A. alliaceus s</i>. <i>str</i>. and two new species described here as <i>A. neoalliaceus</i> and <i>A. vandermerwei</i>. Eight species produced the mycotoxin tenuazonic acid: <i>A. bertholletius</i>, <i>A. caelatus, A. luteovirescens</i>, <i>A. nomius, A. pseudocaelatus</i>, <i>A. pseudonomius, A. pseudotamarii</i> and <i>A. tamarii</i> while the related mycotoxin cyclopiazonic acid was produced by 13 species: <i>A. aflatoxiformans, A. austwickii, A. bertholletius, A. cerealis, A. flavus, A. minisclerotigenes, A. mottae, A. oryzae, A. pipericola, A. pseudocaelatus</i>, <i>A. pseudotamarii, A. sergii</i> and <i>A. tamarii</i>. Furthermore, <i>A. hancockii</i> produced speradine A, a compound related to cyclopiazonic acid. Selected <i>A. aflatoxiformans, A. austwickii, A. cerealis, A. flavus, A. minisclerotigenes, A. pipericola</i> and <i>A. sergii</i> strains produced small sclerotia containing the mycotoxin aflatrem. Kojic acid has been found in all species in section <i>Flavi</i>, except <i>A. avenaceus</i> and <i>A. coremiiformis</i>. Only six species in the section did not produce any known mycotoxins: <i>A. aspearensis</i>, <i>A. coremiiformis, A. lanosus, A. leporis, A. sojae</i> and <i>A. subflavus</i>. An overview of other small molecule extrolites produced in <i>Aspergillus</i> section <i>Flavi</i> is given.