Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2002
Publication Date: N/A
Interpretive Summary: In certain years, aflatoxin contamination of corn, cottonseed, and treenuts can be a serious economic burden for U.S. agriculture. Why aflatoxin contaminates some crops and not others, and the seasonal variability in such contaminations are still mysteries. Numerous strategies have been put forward to prevent aflatoxin contamination in the field or to remove aflatoxin from contaminated crops. However, most of these strategies fail to take into account the natural control that is present in the crops themselves to prevent contamination. To develop a better understanding of the interrelationship between the environment and induction of aflatoxin synthesis, in this paper we studied differences in response of Aspergilli to nitrate and ammoniums salts. Aflatoxin production is controlled by two key regulatory genes named aflR and aflJ. Differences in how these genes are controlled could be key to understanding the nitrate and ammonium effects on aflatoxin because we found differences in the portion of these genes that controls their activity. One of the differences in sequence is in the number of GATA sites. These types of sites are required for gene activity. A strain of Aspergillus from Africa has less sites than strains from the United States. This decreased number of GATA sites correlated with decreased gene activity in nitrate medium. Therefore, a rational explanation for differences in production of aflatoxin on nitrate-rich crops versus production on ammonium-rich crops can be made.
Technical Abstract: In buffered medium, West African Aspergillus flavus SBG isolates were more sensitive to nitrate repression of aflatoxin biosynthesis than were North American SB isolates. Differences in nitrate regulation of aflatoxin biosynthesis in these strains could result, in part, from differences in expression of aflatoxin pathway regulatory genes mediated by AreA, the positive-acting, wide domain transcription factor that is required for expression of nitrate metabolism genes.