Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2019
Publication Date: 2/1/2019
Citation: Hua, S.T., Sarreal, S.L., Chang, P., Yu, J. 2019. Transcriptional regulation of aflatoxin biosynthesis and conidiation in Aspergillus flavus by Wickerhamomyces anomalus WRL-076 for reduction of aflatoxin contamination. Toxins. 11(2):81. https://doi.org/10.3390/toxins11020081.
Interpretive Summary: Aspergillus flavus is a saprophytic and pathogenic fungus. Many isolates of A. flavus are producers of the hepatocarcinogenic aflatoxin (AF) B1, which is often detected in agricultural crops including corn, cotton, peanuts, and tree nuts, and also in many dried fruits and spices. AFB1 contamination is a serious and recurrent problem and causes substantial economic losses worldwide. As part of the arsenal against aflatoxin contamination, biological control agents are touted as environmentally-friendly methods. The yeast Wickerhamomyces anomalus WRL-076 was discovered as an effective antagonist against A. flavus. Real-time Reverse Transcrition –polymerase chain reaction (RT-PCR) has the specificity, sensitivity, and speed to quantify targeted gene fragments. The objective of this study was to apply this technology to eluciadate the biocontrol mechanism of W. anomalus WRL-076 against A. flavus. We analyzed transcription levels of AF biosynthetic gene cluster and conidia regulatory genes in A.flavus. Both the regulatory genes and structures genes were inhibited. Thus the aflaoxin concentration in culture medium was non-dectable and a few spores was produced by the fungal strains when controlled by W. anomalus. The results suggest that the yeast, W. anomalus has the potential to control of aflatoxin and population of A. flavus in food chain to improve food safety.
Technical Abstract: Wickerhamomyces anomalus WRL-076 was screened and identified as an effective biocontrol yeast antagonistic against A. flavus. The molecular mechanism of biocontrol was investigated by transcriptional analysis of aflatoxin biosynthestic gene cluster, conidiation and sclerotial formation in A. flavus. Eight genes, aflR, aflJ, norA, omtA, omtB, ordB, pksA, vbs and ver-1in the aflatoxin biosynthetic pathway cluster were shown to be suppressed ranging from several to 10,000 fold in fungal samples co-cultured with yeast after incubating for 48 hrs. The expression levels of conidiation regulatory genes brlA, abaA and wetA and fluG were decreased in comparison to the control without yeast. SclR, a transcription factor, regulates hyphal morphology and sclerotial formation was also shown to be down-regulated. Consistent with the decreased gene expression levels, the aflatoxin concentrations in cultural medium were greatly reduced to non-detectable; fungal biomass and the number of conidia were significantly reduced by 60% and 99.9% respectively. The VeA gene positively regulates the production of aflatoxins and sclerotial formation was analyzed. Transcriptional levels of S and L strains of A flavus indicated that VeA gene was down-regulated, which in turn would influence AFB1 biosynthesis and sclerotia morphogenesis and conidia formation.