U.S. Department of Agriculture, Agricultural Research Service, Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
Department of Plant Sciences, University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA.
Mycotoxin Res. 2019 Nov;35(4):381-389. doi: 10.1007/s12550-019-00364-w. Epub 2019 Jun 3.
Application of atoxigenic strains to compete against toxigenic strains of Aspergillus flavus strains has emerged as one of the practical strategies for reducing aflatoxin contamination in corn, peanut, and tree nuts. The actual mechanism that results in aflatoxin reduction is not fully understood. Real-time RT-PCR and relative quantification of gene expression protocol were applied to elucidate the molecular mechanism. Transcriptional analyses of aflatoxin biosynthetic gene cluster in dual culture of toxigenic and atoxigenic A. flavus strains were carried out. Six targeted genes, aflR, aflJ, omtA, ordA, pksA, and vbs, were downregulated to variable levels depending on paired strains of toxigenic and atoxigenic A. flavus. Consistent with the decreased gene expression levels, the aflatoxin concentrations in dual cultures were reduced significantly in comparison with toxigenic cultures. Fluorescent images showed fungal hyphae in dual culture displayed green fluorescent, and contacts of live hyphae were seen. A coconut agar plate assay was used to show that toxigenic A. flavus colony produced blue fluorescence under long UV exposure, suggesting that aflatoxin is exported outside fungal hyphae. Furthermore, the assay was applied to demonstrate the potential role of thigmo-regulation in fungal interaction.
应用无毒素菌株来与黄曲霉毒素产生菌株竞争，已成为减少玉米、花生和坚果中黄曲霉毒素污染的实用策略之一。导致黄曲霉毒素减少的实际机制尚未完全了解。实时 RT-PCR 和基因表达谱相对定量方案被应用于阐明分子机制。对产毒和无毒素黄曲霉毒素生物合成基因簇的双培养物进行了转录分析。根据产毒和无毒素黄曲霉毒素的配对菌株，有 6 个靶向基因 aflR、aflJ、omtA、ordA、pksA 和 vbs 被不同程度地下调。与产毒培养物相比，双培养物中的黄曲霉毒素浓度显著降低，与基因表达水平的降低一致。荧光图像显示，双培养物中的真菌菌丝呈现绿色荧光，并且可以看到活菌丝的接触。椰子琼脂平板测定法用于显示在长紫外线暴露下产毒黄曲霉的菌落产生蓝色荧光，表明黄曲霉毒素被运出真菌菌丝外。此外，该测定法被用于证明接触调节在真菌相互作用中的潜在作用。
