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Poster: Biology & Disease Mgmt: Postharvest Pathology & Mycotoxins


Effects of nutrients and microorganisms on aflatoxin production by Aspergillus flavus during successive generations of subculturing
O. OMOLEHIN (1), Y. Ruarang (2), R. Brown (3), Z. Chen (2) (1) Louisiana State University, U.S.A.; (2) Department of Plant Pathology and Crop Physiology, Louisiana State University, U.S.A.; (3) Southern Regional Research Center, USDA-ARS., U.S.A.

Aspergillus flavus infects major agricultural crops, and produces aflatoxin which has been linked to increased liver cancer in humans. Factors such as nutrition, pH and temperature are known to influence A. flavus growth and subsequent aflatoxin production. However, the long-term effects of various media and the presence of other microorganisms on aflatoxin production have not been well studied. In the present study, A. flavus AF13 strain was grown on media containing different levels of nutrients, such as V8, Potato Dextrose Agar (PDA) and Luria Broth (LB), and subcultured for 56 generations. The highest aflatoxin production was observed with A. flavus grown on PDA, which was about 100 times higher than on LB or V8. Aflatoxin production appears to increase with successive transfers of A. flavus on the PDA medium. On the other hand, aflatoxin production seems to decrease slowly with subsequent transfer when A. flavus is grown on V8 or LB medium. At the 39th generation on LB medium, aflatoxin production decreased to a level that was undetectable with HPLC. A. flavus that produced no detectable aflatoxins on LB medium regained the ability to produce high levels of aflatoxin when transferred from LB to PDA medium. These results confirmed earlier studies which have demonstrated that nutrients, especially the carbohydrates in PDA, play a key role in aflatoxin production over time. The impact of microorganisms on aflatoxin production in LB and V8 media will be discussed.