ARS | Publication request: Elucidation of the functional genomics of antioxidant-based inhibition of aflatoxin biosynthesis

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 2007
Publication Date: February 29, 2008
Citation: Kim, J.H., Yu, J., Mahoney, N.E., Chan, K.L., Molyneux, R.J., Varga, J., Bhatnagar, D., Cleveland, T.E., Campbell, B.C. 2008. Elucidation of the functional genomics of antioxidant-based inhibition of aflatoxin biosynthesis. International Journal of Food Microbiology.122(1-2):49-60.

Interpretive Summary: Aflatoxins are carcinogenic compounds that can be found in our food supply. They are produced by certain fungi and are of a major health and food safety concern. Levels of contamination in food commodities is highly regulated. Contaminated foods are a threat to human health and result in large economic losses to producers. In this paper we discover how to prevent aflatoxin production with safe, common natural chemicals. In addition, we show how these compounds work in the fungus so as to turn off the aflatoxin biosynthetic machinery of the fungus. In short, the compounds trick the fungus into "thinking" that it does not need to produce aflatoxin; which are produced by the fungi to protect them from chemical attacks from plants. This information should help in devising methods of breeding crop plants to prevent aflatoxin contamination. It also provides us with significant insights as to how to control the genes that trigger biosynthesis of aflatoxins.

Technical Abstract: Caffeic acid reduces > 95% of aflatoxin production by Aspergillus flavus without affecting fungal growth. Microarray analysis of caffeic acid-treated A. flavus indicated expression of almost all genes in the aflatoxin biosynthetic cluster were down-regulated. The only exceptions were genes norB and the aflatoxin-pathway regulator-gene, aflJ, which showed low expression levels in both treated and control fungi. The secondary metabolism regulator-gene, laeA, also showed little change in expression levels. Alternatively, expression of genes in metabolic pathways increased. The most notable up-regulation of A. flavus expression occurred in four genes that encode alkyl hydroperoxide reductases that detoxify organic peroxides. These findings suggest antioxidants may trigger induction of alkyl hydroperoxide reductases that protect the fungus from oxidizing agents produced during host-plant infection. This detoxification attenuates aflatoxigenesis.