Cumulative effects of non-aflatoxigenic Aspergillus flavus volatile organic compounds to abate toxin production by mycotoxigenic aspergilli

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

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2022
Publication Date: 5/13/2022
Citation: Moore, G.G., Lebar, M.D., Carter-Wientjes, C.H. 2022. Cumulative effects of non-aflatoxigenic Aspergillus flavus volatile organic compounds to abate toxin production by mycotoxigenic aspergilli. Toxins. 14:340. https://doi.org/10.3390/toxins14050340.
DOI: https://doi.org/10.3390/toxins14050340

Interpretive Summary: We have demonstrated previously that growing each of three aflatoxin producing A. flavus strains in the presence of specific gases, produced by non-aflatoxin-producing A. flavus strains (biocontrol), could greatly reduce production of this potent toxin. This finding suggested that the effectiveness of A. flavus biocontrol strains may involve production of specific gases. In this study, we tested various combinations of the three most impactful gases to see if they would impact fungal growth, and/or offer complete inhibition of aflatoxin. We exposed the same three toxin producing strains to combinations of two (and all three) gases, and we expanded our toxin analysis to include additional fungal toxins. Like our previous observations involving individual gases, fungal growth remained minimally impacted. Aflatoxin production was again significantly reduced in all strains; however, no single combination was able to completely prevent production of any of the toxins we examined. Our findings show that combining one or more gases can still inhibit production of several agriculturally important fungal toxins. Therefore, other gases (individually or in combination) are worth testing as post-harvest biocontrol treatments to ensure the prolonged effectiveness of pre-harvest biocontrol efforts.

Technical Abstract: Using the same four Aspergillus strains from Louisiana (LA1-LA4), we exposed each of the strains to three different volumes of combined VOCs. Various combinations were created involving two or three of the most effective compounds from our previous study (2,3-dihydrofuran, 3-octanone and decane), considered unique to strains of non-aflatoxigenic A. flavus, to study their impacts on growth as well as production of eight mycotoxins: aflatoxins B1, B2, G1, G2, cyclopiazonic acid (CPA), aflatrem, aflavazole and aflavinine. Growth was again assessed through daily measurements of colony diameter (in mm) on Yeast Extract Sucrose (YES) medium. We found that combining VOCs still offered minimal reductive impact, and in more cases increased growth. Toxin production was assessed through Ultra-High Performance Liquid Chromatography (UPLC) and Liquid Chromatography-Mass Spectrometry (LC-MS). Unexpectedly, LA1 (a non-aflatoxigenic and CPA-negative strain) was found to produce the toxic secondary metabolites aflatrem, aflavazole and aflavinine. Reductions in these compounds were observed during this study, but their presence in LA1 may prevent its use as a biocontrol strain. As observed with individual VOCs, aflatoxin production was greatly reduced in our three aflatoxigenic strains (LA2-LA4). Although not completely inhibited as observed in our previous study involving individual VOCs, there were substantial reductions in CPA production. In most cases, reductions in production of aflatrem, aflavazole and aflavinine were observed. Our findings continue to support that production of VOCs by non-aflatoxigenic A. flavus strains could contribute to the effectiveness of A. flavus biocontrol.