The role of extrolites secreted by nonaflatoxigenic Aspergillus flavus in biocontrol efficacy.

Abstract

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.