Submitted to: Journal of Food Additives & Contaminants
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/17/2007
Publication Date: 10/1/2007
Citation: Wilkinson, J.R., Yu, J., Abbas, H.K., Scheffler, B.E., Kim, H.S., Nierman, W.C., Bhatnagar, D., Cleveland, T.E. 2007. Aflatoxin formation and gene expression in response to carbon source media shift in Aspergillus parasiticus. Journal of Food Additives & Contaminants. 24(10):1051-1060. Interpretive Summary: Aflatoxins are toxic and carcinogenic compounds produced by fungal molds. It contaminates agricultural food and feed commodities. Health risk to human and animal as well as economic losses due to aflatoxin contamination are significant. In order to devise strategies to control aflatoxin contamination, A. parasiticus was evaluated during a shift from a medium with low concentration of simple sugars, Yeast Extract (YE), to a similar medium with sucrose, Yeast Extract Sucrose (YES). Functional genomic studies by microarray analysis identified 56 genes that have the potential to function in the regulation of aflatoxin biosynthesis.
Technical Abstract: Aflatoxins are toxic and carcinogenic polyketide metabolites produced by fungal species, including Aspergillus flavus and A. parasiticus. The biosynthesis of aflatoxins is modulated by many environmental factors, including the availability of a carbon source. The gene profile of A. parasiticus was evaluated during a shift from a medium with low concentration of simple sugars, Yeast Extract (YE), to a similar medium with sucrose, Yeast Extract Sucrose (YES). Total RNA and aflatoxins (B1, B2, G1 and G2) were quantified from fungal mycelia harvested pre- and post-shifting. When compared to YE media, YES caused reduction of the aflatoxin levels by 3 hours post-shifting and they remained low well past 12 hours post-shift. By 18 hours, post-shift aflatoxin levels had returned to half of the levels in YE. Aflatoxin levels did not exceed the levels in YE until 24 hours post shift, at which time point a 10-fold increase was observed. Microarray analysis comparing the RNA samples from the 48 hour YE culture to the YES samples identified a total of 2120 genes that were expressed across all experiments, including most of the aflatoxin biosynthesis genes. One-way analysis of variance (ANOVA) identified 56 genes that were expressed with significant variation across all time points. Three genes responsible for converting norsolorinic acid to averantin were identified among these significantly expressed genes. The potential role of these genes involvement in the regulation of aflatoxin biosynthesis is discussed.