Insight into the development of biocontrol strategy through molecular mechanisms of yeast and Aspergillus flavus interactions

Aflatoxins are extremely potent natural carcinogens and a major food safety concern because of contamination of food commodities. The European Union (EU) and Japan have set threshold levels at less than 4 ppb. These low tolerance levels increase potential rejection of agricultural commodities from exporting countries. The major aflatoxin-producing fungus, Aspergillus flavus is ubiquitous in agricultural soils and has a broad ecological niche. Saprophytic yeasts have been studied as promising approach to manage aflatoxin contamination. Advancement in the use of molecular techniques including genomics, transcriptomics are providing a powerful tool to dissect the complex interactions between the yeast and the fungus. A bioassay has been developed to screen for effective yeasts inhibiting both the growth of A. flavus and aflatoxin production. Pichia anomala WRL-076 was identified as biocontrol agent. The molecular mechanisms were characterized by the temporal transcriptome response of P. anomala to A. flavus in a liquid growth medium. Comparison of yeast gene expression with and without A. flavus, a large number of genes were differentially expressed. Specifically, genes involved in protein phosphorylation, protein kinase, DNA-templated regulation of transcription, and microtubule-based movement. The major volatile compound produced by P. anomala WRL-076 is 2-phenylethanol (2-PE). It inhibited spore germination and aflatoxin production of A. flavus. The inhibition was correlated with significant down regulation of clustering AF biosynthesis genes as evidenced by several to greater than 10,000-fold decrease in gene expression.