US Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, New Orleans, LA, USA.
J Appl Microbiol. 2019 Apr;126(4):1257-1264. doi: 10.1111/jam.14175. Epub 2019 Feb 7.
Field control of aflatoxin contamination is thought to occur through competitive exclusion of native aflatoxigenic fungi by introduced nonaflatoxigenic Aspergillus flavus biocontrol strains. In this study, we explored another possible mechanism that could increase the efficacy of biocontrol strains-the production of secreted compounds termed extrolites.
Using four Aspergillus strains (one nonaflatoxigenic and three aflatoxigenic) from the same geographic region (Louisiana), we devised experiments whereby each aflatoxigenic strain was grown on media that had first been colonized by the nonaflatoxigenic strain. We observed noticeable reduction in growth and reduced production of aflatoxin and cyclopiazonic acid for all three aflatoxigenic strains when grown in the presence of extrolite secretions from the nonaflatoxigenic strain.
We provide evidence that biocontrol strain extrolites may improve the efficacy of pre and postharvest aflatoxin reduction.
Our finding, that extrolites secreted by nonaflatoxigenic A. flavus strains potentially abate growth and toxin levels of aflatoxin-producing strains, should allow for us to elucidate the mechanism of how the reduction in toxigenic strains occurs, and potentially identify better biocontrol strains. Identification and isolation of the active extrolites may afford a supplemental method to mitigate aflatoxin production.
人们认为通过引入非产黄曲霉毒素的 Aspergillus flavus 生物防治菌株对本地产黄曲霉毒素真菌进行竞争性排斥，可实现田间黄曲霉毒素污染的控制。在这项研究中，我们探索了另一种可能提高生物防治菌株功效的机制，即产生分泌化合物，称为代谢产物。
我们使用来自同一地理区域（路易斯安那州）的四个曲霉属菌株（一个非产黄曲霉毒素和三个产黄曲霉毒素），设计了这样的实验，即每个产黄曲霉毒素的菌株都在最初被非产黄曲霉毒素菌株定植的培养基上生长。当在非产黄曲霉毒素菌株的代谢产物存在的情况下生长时，我们观察到所有三个产黄曲霉毒素的菌株的生长明显减少，并且黄曲霉毒素和环匹阿尼酸的产量降低。
我们提供了证据表明生物防治菌株的代谢产物可能提高了收获前和收获后降低黄曲霉毒素的功效。
我们的发现，即非产黄曲霉毒素 A. flavus 菌株分泌的代谢产物可能会抑制产黄曲霉毒素菌株的生长和毒素水平，这应该使我们能够阐明减少产毒菌株的发生机制，并可能确定更好的生物防治菌株。鉴定和分离活性代谢产物可能为减轻黄曲霉毒素生产提供一种补充方法。
