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The School of Biology welcomes Ronald Riley, research toxicologist at the USDA Research Service, on "When Good Mold Goes Bad – from Auvergne Bleu to Zinfandel and Everything in Between."
Abstract:
Fungal secondary metabolites have been used to great advantage by humans for a multitude of purposes. In the food industry, fermentation using specific strains of fungi has been used for thousands of years to produce foods and beverages that are held in high esteem in many cultures. And in some cases, they have provided the leads for important new drugs, such as the new immunosuppressive drug Fingolimod (FTY720) that is based on a fungal secondary metabolite (myriocin) that is a sphingoid base analog and modulator of sphingolipid metabolism and signaling.
Nonetheless, not all fungal secondary metabolites are beneficial. Mycotoxins are secondary metabolites from fungi that are known or suspected to be involved in plant, animal and human disease. The total number of mycotoxins in foods is unknown but estimates range from a few hundred to a few thousand. Currently, there are six groups of mycotoxins that create significant problems for agriculture and the food industry. These are aflatoxins, ergot-alkaloids, fumonisins, ochratoxins, trichothecenes and zearalenone.
Each of these groups is comprised of several unique chemical structures which are produced via specific fungal biosynthetic pathways. For example, fumonisins are produced by several Fusarium species which are common contaminants of maize. Recently, several Aspergillus species have been shown to produce fumonisins on dried vine fruits and they have been detected in wine.
Climate change is predicted to exacerbate problems with mycotoxins since stressed plants and warm humid and drought conditions are often conducive to mold growth and mycotoxin production in the field. This is especially true with fumonisins which are sphingoid base analogs and potent inhibitors of ceramide synthase a key enzyme in the biosynthesis of sphingolipids. The fumonisins cause several animal diseases and are virulence/pathogenicity factors in maize seedling disease. In all cases, the diseases are closely linked to disruption of sphingolipid metabolism.
The fumonisins are also suspected of being contributing factors to disease in humans, most notably, neural tube defects in areas of the world where maize is consumed in large amounts and diets are likely to be deficient in folate and other vitamins critical for normal neural tube closure. The hypothesis that fumonisin-induced disruption of sphingolipid metabolism could contribute to increased risk of birth defects is plausible but not proven.
On the positive side fumonisin B1 has proven to be a very useful research tool for revealing the importance of ceramide and sphingoid bases and their metabolites in numerous cellular processes. Thus, the discovery of these toxic fungal metabolites has helped to reveal the dangers of disrupted sphingolipid metabolism in animal and plant heath and also has aided in the discovery of sphingolipid-dependent processes that have the potential to serve the greater good.
