Production of inhibitory extrolites is a shared trait among non-aflatoxigenic Aspergillus flavus

Authors: Moore, Geromy; Lebar, Matthew; Sweany, Rebecca; Lohmar, Jessica; Carter Wientjes, Carol

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2025
Publication Date: 4/4/2025
Citation: Moore, G.G., Lebar, M.D., Sweany, R.R., Lohmar, J.M., Carter Wientjes, C.H. 2025. Production of inhibitory extrolites is a shared trait among non-aflatoxigenic Aspergillus flavus. Journal of Applied Microbiology. 136(5). Article lxaf084. https://doi.org/10.1093/jambio/lxaf084.
DOI: https://doi.org/10.1093/jambio/lxaf084

Interpretive Summary: In order to improve A. flavus biocontrol efficacy, we must first understand how it reduces aflatoxin production. In a previous study using four strains from Louisiana, we proved that one way A. flavus biocontrol strains reduce growth and/or aflatoxin production in competitor strains is by secreting metabolites (i.e., extrolites) with inhibitory properties. In this study, we showed production of inhibitory extrolites is a trait shared among non-aflatoxigenic [biocontrol] strains. We expanded our investigation to include four Aspergillus strains from each of three different geographic regions (Arizona, Georgia and Mississippi). Although extrolites from each region's non-aflatoxigenic strain were inhibitory, those produced by the strain from Arizona (AF36) exhibited the strongest impact by reducing growth and/or toxin production by all the examined strains. This suggests extrolite secretion likely underscores the competitive exclusion mechanism often associated with this biocontrol strains. Characterization of inhibitory extrolites would allow us to screen for better biocontrol strains. Exploitation of these extrolites could offer an effective post-harvest treatment to help mitigate aflatoxin production.

Technical Abstract: Using one non-aflatoxigenic [biocontrol] and three aflatoxigenic strains, from each of three geographic regions (Arizona, Georgia and Mississippi), we devised experiments whereby each aflatoxigenic strain was grown on two types of YES medium (solid and liquid) that had first been colonized by the biocontrol strain. In this way, secreted extrolites from the biocontrol strain infiltrated the substrate. For each location, we observed noticeable reduction in growth and production of mycotoxins by the respective aflatoxigenic strains. AZ1 (AF36 from Arizona) exhibited the greatest negative impact, effectively reducing growth and toxin production in strains from all examined regions, including Louisiana. However, a linear correlation between growth reduction and toxin reduction was only observed with the GA strains. We provide additional support that A. flavus biocontrol strains share the ability to produce highly inhibitory extrolites, although they were not all equally as impactful. Use of these extrolites may improve biocontrol efficacy, especially at the post-harvest stage.