The potential role of fungal volatile organic compounds in Aspergillus flavus biocontrol efficacy

Authors: Moore, Geromy; Lebar, Matthew; Carter-Wientjes, Carol; Gilbert, Matthew

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2021
Publication Date: 6/9/2021
Citation: Moore, G.G., Lebar, M.D., Carter-Wientjes, C.H., Gilbert, M.K. 2021. The potential role of fungal volatile organic compounds in Aspergillus flavus biocontrol efficacy. Biological Control. 160:104686. https://doi.org/10.1016/j.biocontrol.2021.104686.
DOI: https://doi.org/10.1016/j.biocontrol.2021.104686

Interpretive Summary: Pre-harvest application of inherently non-aflatoxigenic Aspergillus flavus strains is an effective biocontrol strategy to minimize aflatoxin contamination of agricultural commodities, but researchers still do not fully understand how A. flavus biocontrol strains effect control over toxigenic strains/species. Competitive exclusion is a prominent theory cited as a mechanism of biocontrol that results in loss of aflatoxin production. In this study, we tested the potential for A. flavus volatile organic compounds (VOCs) to serve as regulators of mycotoxin production. Four of the five VOCs tested (reportedly unique to non-aflatoxigenic A. flavus) reduced production of both mycotoxins of interest, and each of two of those VOCs significantly reduced aflatoxin B1 levels while also completely inhibiting CPA production in one strain. Our findings offer evidence that the mechanism of control may involve production of one or more VOCs and offer potential to improve pre-harvest biocontrol strain selection (selecting for enhanced production of these compounds) or to supplement current biocontrol efforts through post-harvest exposure to non-aflatoxigenic A. flavus VOC-related chemicals. Additionally, in this study we report findings from a genomic investigation for one of the Louisiana strains (given to us as an A. parasiticus strain) that produced a mycotoxin uncharacteristic of A. parasiticus.

Technical Abstract: Using four Aspergillus strains (one non-aflatoxigenic and three aflatoxigenic) from the same geographic region (Louisiana), we devised experiments whereby we exposed the strains to three different volumes of each of five VOCs unique to non-Louisiana strains of aflatoxigenic A. flavus (benzaldehyde, benzyl alcohol, eucalyptol, hexane, isoamyl acetate), and non-aflatoxigenic A. flavus (2-methyl-1-butanol, 2,3-dihydrofuran, 3-octanone, decane, and trans-2-methyl-2-butenal), to study their impacts on growth as well as production of two mycotoxins: aflatoxin B1 and cyclopiazonic acid (CPA). Growth was assessed through daily measurements of colony diameter (in mm) on Yeast Extract Sucrose (YES) medium, which is a good substrate for in vitro mycotoxin analysis. We found that overall growth of the fungi was minimally impacted by exposure to our chosen VOCs. Toxin production was assessed through Ultra-High Performance Liquid Chromatography (UPLC). Contrary to growth, toxin production was greatly affected and highly variable between strains and VOCs. A reduction in aflatoxin production did not always guarantee a reduction in CPA production. Unexpected morphological variations were observed for two of the toxigenic strains after exposure to the VOC, benzyl alcohol. We also conducted multi-locus sequence typing of several conserved loci for strain LA4 (likely not an A. parasiticus strain) to elucidate its true species identity. Based on our findings, LA4 may be a strain of A. novoparasiticus, but it could also be an interspecific hybrid due to its ability to produce CPA, a compound not capable of being produced by A. parasiticus or the Type strain of A. novoparasiticus.