Transcriptional Regulation of Aflatoxin Biosynthesis and Conidiation in Aspergillus flavus by Wickerhamomyces anomalus WRL-076 for Reduction of Aflatoxin Contamination.

Sui Hua,Siov Sarreal,Jiujiang Yu,Perng-Kuang Chang

doi:10.3390/toxins11020081

Abstract

Aspergillus flavus is a ubiquitous saprophytic fungus found in soils across the world. The fungus is the major producer of aflatoxin (AF) B1, which is toxic and a potent carcinogen to humans. Aflatoxin B1 (AFB1) is often detected in agricultural crops such as corn, peanut, almond, and pistachio. It is a serious and recurrent problem and causes substantial economic losses. Wickerhamomyces anomalus WRL-076 was identified as an effective biocontrol yeast against A. flavus. In this study, the associated molecular mechanisms of biocontrol were investigated. We found that the expression levels of eight genes, aflR, aflJ, norA, omtA, omtB, pksA, vbs, and ver-1 in the aflatoxin biosynthetic pathway cluster were suppressed. The decreases ranged from several to 10,000 fold in fungal samples co-cultured with W. anomalus. Expression levels of conidiation regulatory genes brlA, abaA, and wetA as well as sclerotial regulatory gene (sclR) were all down regulated. Consistent with the decreased gene expression levels, aflatoxin concentrations in cultural medium were reduced to barely detectable. Furthermore, fungal biomass and conidial number were significantly reduced by 60% and more than 95%, respectively. The results validate the biocontrol efficacy of W. anomalus WRL-076 observed in the field experiments.

Highlights

Aspergillus flavus is a saprophytic and pathogenic fungus
We examined the influence of W. anomalus on Aflatoxin B1 (AFB1) production on the four toxigenic A. flavus
Consistent with the decreased gene expression levels, the aflatoxin concentrations medium were medium greatly reduced to non-detectable levels

Summary

Introduction

Aspergillus flavus is a saprophytic and pathogenic fungus. Many isolates of A. flavus produce the hepatocarcinogenic aflatoxin (AF) B1 , which is often detected in agricultural crops including corn, cotton, peanuts, and tree nuts, and in many dried fruits and spices. AFB1 contamination in food results in substantial economic losses worldwide [1,2,3,4,5,6,7]. More than 100 countries have established specific regulation guidelines limiting allowable amounts of AFB1 in foodstuffs [8,9]. Major importers of agricultural commodities have imposed threshold levels for AFB1 below 10 μg/kg, and these restrictions have had a major negative impact on the exportability of a number of crops [10].

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