Dual culture of atoxigenic and toxigenic strains of Aspergillus flavus to gain insight into repression of aflatoxin biosynthesis and fungal interaction

Authors: Hua, Sui Sheng; PARFITT, DAN - University Of California, Davis; Sarreal, Siov; Sidhu, Gaganjot

Submitted to: Mycotoxin Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2019
Publication Date: 6/3/2019
Citation: Hua, S.T., Parfitt, D., Sarreal, S.L., Sidhu, G.K. 2019. Dual culture of atoxigenic and toxigenic strains of Aspergillus flavus to gain insight into repression of aflatoxin biosynthesis and fungal interaction. Mycotoxin Research. https://doi.org/10.1007/s12550-019-00364-w.
DOI: https://doi.org/10.1007/s12550-019-00364-w

Interpretive Summary: Many strains of Aspergillus flavus are producers of a potent hepatocarcinogenic aflatoxin (AF) B1, which is often detected in agricultural crops. 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. Application of atoxigenic strains to compete against aflatoxigenic strains of A. flavus strains has emerged as one of the practical strategies for reducing aflatoxins contamination in corn, peanut and tree nuts. The actual mechanism that results in this reduction is not fully understood. 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 illuminate the biocontrol mechanism. This is the first report to demonstrate that several positive regulatory genes in aflatoxigenic A. flavus strains were repressed resulting in prevention of aflatoxin biosynyhesis. Aflatoxin concentrations were reduced in all experimental samples.

Technical Abstract: Application of atoxigenic strains to compete against aflatoxigenic A. flavus strains has emerged as one of the practical strategies for reducing aflatoxins contamination in corn, peanut and tree nuts. The actual mechanism that results in this reduction is not fully understood. Three atoxigenic A. flavus strains were each paired with a aflatoxigenic strain to start a dual culture in potato dextrose broth. RNA was extracted from each sample and used for Real-Time qRT-PCR assay. The molecular mechanism of biocontrol was investigated by transcriptional analysis of aflatoxin biosynthestic gene cluster. Eight genes, aflR, aflJ, norA, omtA, omtB, ordB, pksA, vbs and ver-1in the aflatoxin biosynthetic pathway cluster, were suppressed to variable levels depending on paired strains. Transcriptional levels of the global regulatory VeA gene was down-regulated in all dual cultures including both S and L strains of afltoxigenic A. flavus. The decreased expression of VeA would reduce AFB1 biosynthesis. A coconut agar plate assay was developed to demonstrate touch inhibition and visual aflatoxin reduction.