|Rajasekaran, Kanniah - Rajah|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 4/12/2007
Publication Date: 9/15/2007
Citation: Bhatnagar, D., Rajasekaran, K., Brown, R.L., Cary, J.W., Yu, J., Cleveland, T.E. 2008. Genetic and Biochemical Control of Aflatoxigenic Fungi. In: Wilson, C.L. (editor). Microbial Food Contamination. Boca Raton, Fl: CRC Press. 17:395-425.
Technical Abstract: Aflatoxins are polyketide derived, toxic and carcinogenic secondary metabolites produced primarily by two fungal species, Aspergillus flavus and A. parasiticus, on crops such as corn, peanuts, cottonseed, and treenuts. Regulatory guidelines issued by the U.S. Food and Drug Administration (FDA) prevent sale of commodities if contamination by these toxins exceeds certain levels. The biosynthesis of these toxins has been extensively studied. About 15 stable precursors have been identified. The genes involved in encoding the proteins required for the oxidative and regulatory steps in the biosynthesis are clustered in a 70 kb portion of chromosome 3 in the A. flavus genome. With the characterization of the gene cluster, new insights into the cellular processes that govern the genes involved in aflatoxin biosynthesis have been revealed, but the signaling processes that turn on aflatoxin biosynthesis during fungal contamination of crops are still not well understood. New molecular technologies, such as genomics and gene microarray analyses, quantitative polymerase chain reaction (PCR) to understand how physiological stress, environmental and soil conditions, receptivity of the plant and fungal virulence lead to episodic outbreaks of aflatoxin contamination in certain commercially important crops. With this fundamental understanding of the fungus and the molecular basis for host-plant resistance, we will be better able to better design strategies for preventing fungal invasion of crops or toxin production. Comparisons of aflatoxin producing species with other fungal species that retain some of the genes required for aflatoxin formation is expected to provide insight into the evolution of the aflatoxin gene cluster, and its role in fungal physiology. Therefore, information on how and why the fungus makes the toxin will be valuable for developing an effective and lasting strategy for control of aflatoxin contamination. With the availability of the genomic DNA sequences, sensitive methods to detect DNA of the fungi (Aspergillus), which are capable of producing aflatoxins, could be developed for screening foods and feeds in order to ensure the safety of food and feed.