Global Population Structure and Aflatoxin Chemotype Diversity in Aspergillus Section Flavi

The genus Aspergillus is comprised of over 250 species that are grouped into sections based on similar phenotypic characters. Section Flavi includes species that have great economic impact on a global scale since they exist all over the world. Beneficial species such as Aspergillus oryzae are integral to fermentation of soy sauce and sake, but this research focuses on those species in Section Flavi that negatively affect global economies. Among these are species that are pathogenic on important agricultural commodities, but that also have the potential to produce carcinogenic substances known as aflatoxins. These aflatoxins are synthesized in a biosynthetic pathway that involves at least 25 clustered genes. Two of the most common species that produce aflatoxins are Aspergillus flavus Link and Aspergillus parasiticus Speare. Since the first publicized outbreak of aflatoxins with Turkey X disease over 40 years ago, researchers have sought to control contamination of food by aflatoxin producing Aspergilli. Pre-harvest biocontrol using E.P.A. approved biopesticides is currently one of the preferred methods of control using atoxigenic A. flavus strains to competitively exclude indigenous aflatoxin producers. An important consideration for the success of these atoxigenic strains as biocontrol is that these fungi are considered asexual and incapable of recombining with indigenous strains. Recent discoveries of mating type genes in these fungi, and subsequent discoveries of sexual states in A. flavus and A. parasiticus, call into question the stability of the biocontrol strains since the potential for them to outcross and regain aflatoxigenicity exists.