AFLATOXIN CONTROL THROUGH TARGETING MECHANISMS GOVERNING AFLATOXIN BIOSYNTHESIS IN CORN AND COTTONSEED
Location: Food and Feed Safety Research
Title: TEMPERATURE DEPENDENT MOLECULAR REGULATION OF AFLATOXIN BIOSYNTHESIS
Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 2006
Publication Date: May 21, 2006
Citation: Obrian, G.R., Georgiana, D.R., Wilkinson, J.R., Yu, J., Bhatnagar, D., Cleveland, T.E., Payne, G.A. 2006. Temperature dependent molecular regulation of aflatoxin biosynthesis. In: Proceedings of the American Society for Microbiology Annual Meeting, May 21-26, 2006, Orlando, FL. Abstract #O-063, p. 433.
The molecular regulation of aflatoxin biosynthesis is complex and influenced by several environmental conditions. As an example, aflatoxins are produced optimally at 28 degrees C but not at all at 37 degrees C, the optimum temperature for fungal growth. One explanation for this response is a temperature sensitive factor(s) that controls aflatoxin biosynthesis. This factor(s) could be an activator of aflatoxin synthesis that is active below 37 degrees C and inactive at higher temperatures or an inhibitor of aflatoxin synthesis that is only active at higher temperatures. To determine if elevated temperatures affect gene transcription in Aspergillus flavus, we used DNA microarrays containing 5002 elements and analyzed gene expression under conducive (28 degrees C) and non-conducive (37 degrees C) temperatures. As anticipated, we found that the aflatoxin biosynthetic genes were much more highly expressed at 28 degrees C relative to 37 degrees C. In addition to the aflatoxin biosynthetic genes, numerous other genes were also more highly expressed at 28 degrees C. Different sets of genes were more highly expressed at 37 degrees C. To determine if an activator of aflatoxin is produced at 28 degrees C, cultures were grown for 16 hr at 28 degrees C and transferred to 37 degrees C or to 28 degrees C. We anticipated that once aflatoxin production was induced at 28 degrees C, it would continue to be produced when cultures were transferred to 37 degrees C. However, we found no additional aflatoxin produced when the cultures were transferred to 37 degrees C. In contrast, cultures grown first at 37 degrees C and transferred to 28 degrees C produced aflatoxin. Because AflR is the transcriptional regulator of the aflatoxin pathway, it is likely involved in the temperature response. However, evidence suggests that AflR may not be the only factor; 1) the shift from 28 degrees C to 37 degrees C that negated additional aflatoxin formation would tend to argue against this since aflatoxin biosynthetic gene transcripts are already present before the shift. 2) AflR is present in cultures grown at 37 degrees C (Liu et al. 1998. Food Agric. Immunol. 9:289-298). An analysis of gene transcription profiles over a range of temperatures are planned to better characterize the factors involved in the regulation of aflatoxin by temperature.