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Fitness of Aspergillus flavus in soil is affected by temperature and soil microbial community

Milton Drott: Cornell University

<div>Aflatoxin, produced by <em>Aspergillus flavus</em>, commonly contaminates corn and other crops causing acute toxicosis, cancer, immune suppression, and stunted growth in children. Biocontrol strategies have recently been utilized in attempts to decrease aflatoxin contamination by applying large numbers propagules from of non-aflatogenic <em>A. flavus</em> strains to agricultural soils. Despite the increasing use of this method, the relationships between <em>A. flavus</em>, the soil community, and aflatoxin have remained unexplored. We hypothesized that aflatoxin production of the fungus mediates its ability to interact with soil microbial communities. To test this hypothesis we compared the fitness of naturally occurring aflatoxigenic and non-aflatoxigenic fungal isolates in autoclaved and natural field soils at suboptimal, optimal and stressful temperatures for <em>A. flavus</em> growth (25, 37, 42 °C). Fitness was measured using qPCR estimates of fungal DNA. In natural soils at 37 °C, the addition of aflatoxins to soil, as well as the ability of the fungus to produce aflatoxin, decreased the fitness of <em>A. flavus</em>. At 25 °C we observed a suppressive effect of the natural soils against both chemotypes of <em>A. flavus</em>. We did not observe any differences in fungal fitness in sterile soils. We further investigated the potential for aflatoxin to impact microbial communities using amplicon sequencing at optimal growth temperatures. We observed significant changes in alpha and beta diversity of soil bacterial communities with the addition of aflatoxin and in the presence of aflatoxigenic isolates. We did not, however, observe any specific organisms responsible for the decreased growth we observed in the presence of aflatoxin. Our results provide evidence that aflatoxin production by <em>A. flavus</em> affects the fungus's growth when interacting with soil microbial communities.</div>

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