When mycotoxins come in bunches: Fumonisin production by Aspergillus niger in grapes
J. D. PALUMBO (1), T. L. O’Keeffe (1). (1) USDA ARS WRRC, Albany, CA, U.S.A.
<i>Aspergillus niger</i> is one of several black-spored <i>Aspergillus</i> species that commonly occur as epiphytes of healthy grapes, and as causative agents of black bunch rot and raisin mold. Genome sequencing of <i>A. niger</i> revealed the presence of a previously unknown gene cluster homologous to the fumonisin biosynthetic gene cluster in <i>Fusarium</i> species. This led to the discovery that <i>A. niger</i> does indeed produce fumonisins, most predominantly fumonisin B<sub>2</sub> (FB<sub>2</sub>). Because of the ubiquity of <i>A. niger</i> on grapes, it is not surprising that fumonisin contamination of grape products such as wine and raisins is widespread. For example, in one study of raisins collected from five distinct vineyards, we detected fumonisin in 90% of the samples. The majority of <i>A. niger</i> strains, as well as strains of the phylogenetically distinct species <i>A. awamori</i>, produce FB<sub>2</sub>. Analyses of the fumonisin biosynthetic gene cluster in FB<sub>2</sub>-nonproducing strains indicate that deletion of most of the gene cluster occurs in FB<sub>2</sub>-nonproducing <i>A. awamori</i> strains, whereas in FB<sub>2</sub>-nonproducing <i>A. niger</i> strains, the gene cluster is intact. This distinction may be useful in monitoring FB<sub>2</sub>-producing and -nonproducing <i>A. niger</i> and <i>A. awamori</i> populations, to predict fumonisin contamination of grapes, and to investigate seasonal variation in the distribution of these species within and among vineyards.
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