Amino acid supplementation reveals differential regulation of aflatoxin biosynthesis in Aspergillus flavus NRRL 3357 and Aspergillus parasiticus SRRC 143

Abstract

Aflatoxins are toxic and carcinogenic secondary metabolites produced by the fungi Aspergillus flavus and Aspergillus parasiticus. To better understand the molecular mechanisms that regulate aflatoxin production, the biosynthesis of the toxin in A. flavus and A. parasticus grown in yeast extract sucrose media supplemented with 50 mM tryptophan (Trp) were examined. Aspergillus flavus grown in the presence of 50 mM tryptophan was found to have significantly reduced aflatoxin B(1) and B(2) biosynthesis, while A. parasiticus cultures had significantly increased B(1) and G(1) biosynthesis. Microarray analysis of RNA extracted from fungi grown under these conditions revealed 77 genes that are expressed significantly different between A. flavus and A. parasiticus, including the aflatoxin biosynthetic genes aflD (nor-1), aflE (norA), and aflO (omtB). It is clear that the regulatory mechanisms of aflatoxin biosynthesis in response to Trp in A. flavus and A. parasiticus are different. These candidate genes may serve as regulatory factors of aflatoxin biosynthesis.

<i>Aspergillus flavus</i> Secondary Metabolites: More than Just Aflatoxins

“…Inactivation of nsdC resulted in decreased aflatrem production, as well as decreased expression of genes encoding the backbone enzymes for penicillin, asparasone, ustiloxin B, and AF biosynthesis 26) . Clusters 5,20,41,44, and others also showed altered transcriptional profiles in the nsdC knockout strain. Metabolites produced by these clusters remain to be identified.…”

“…Microarray technology was among early approaches characterizing A. flavus gene function 42) , natural antisense transcripts 43) , and secondary metabolism, with an initial focus on AF regulation [44][45][46][47][48] . Subsequent to this, the examination of other SM gene clusters using customized microarrays were reported 8,29,49,50) .…”

Aflatoxin Biosynthetic Pathway and Pathway Genes

“…These results demonstrate that AflR is specifically involved in the regulation of aflatoxin biosynthesis. Indeed, all 23 upregulated genes, identified by transcription profiling using DNA microarray assays comparing wild-type and aflR-deleted A. parasiticus strains, have the consensus AflR binding motif in their promoter regions (Meyers et al, 1998;Price et al, 2006;Wilkinson et al, 2007a;Wilkinson et al, 2007b).…”

Strategies in Prevention of Preharvest Aflatoxin Contamination in Peanuts: Aflatoxin Biosynthesis, Genetics and Genomics

“…Certain amino acids also can have opposing effects on aflatoxin production (Payne and Hagler, 1983). Recent studies using A. flavus show that tryptophan inhibits aflatoxin formation while tyrosine spikes aflatoxin production (Wilkinson et al, 2007). Micronutrients (metal ions) were also reported to affect aflatoxin pathway gene expression (Bennett et al, 1979;Cuero et al, 2003).…”