Abstract
Aflatoxins are potent Aspergillus mycotoxins that contaminate food and feed, thereby impacting health and trade. Biopesticides with atoxigenic Aspergillus flavus isolates as active ingredients are used to reduce aflatoxin contamination in crops. The mechanism of aflatoxin biocontrol is primarily attributed to competitive exclusion but, sometimes, aflatoxin is reduced by greater amounts than can be explained by displacement of aflatoxin-producing fungi on the crop. Objectives of this study were to (i) evaluate the ability of atoxigenic A. flavus genotypes to degrade aflatoxin B1 (AFB1) and (ii) characterize impacts of temperature, time, and nutrient availability on AFB1 degradation by atoxigenic A. flavus. Aflatoxin-contaminated maize was inoculated with atoxigenic isolates in three separate experiments that included different atoxigenic genotypes, temperature, and time as variables. Atoxigenic genotypes varied in aflatoxin degradation but all degraded AFB1 >44% after 7 days at 30°C. The optimum temperature for AFB1 degradation was 25 to 30°C, which is similar to the optimum range for AFB1 production. In a time-course experiment, atoxigenics degraded 40% of AFB1 within 3 days, and 80% of aflatoxin was degraded by day 21. Atoxigenic isolates were able to degrade and utilize AFB1 as a sole carbon source in a chemically defined medium but quantities of AFB1 degraded declined as glucose concentrations increased. Degradation may be an additional mechanism through which atoxigenic A. flavus biocontrol products reduce aflatoxin contamination pre- or postharvest. Thus, selection of optimal atoxigenic active ingredients can include assessment of both competitive ability in agricultural fields and their ability to degrade aflatoxins.
Highlights
Aflatoxins are potent Aspergillus mycotoxins that contaminate food and feed, thereby impacting health and trade
Ten atoxigenic genotypes of A. flavus that are active ingredients in five commercially available aflatoxin biocontrol products were evaluated for ability to degrade aflatoxins
Previous research has shown that some atoxigenic A. flavus biocontrol strains reduce aflatoxin contamination more than can be explained by competitive exclusion alone (Cotty and Bayman 1993; Mehl and Cotty 2010), suggesting that additional mechanisms of aflatoxin biocontrol may be in play
Summary
Aflatoxins are potent Aspergillus mycotoxins that contaminate food and feed, thereby impacting health and trade. Aflatoxins are naturally occurring carcinogenic secondary metabolites produced by several species in Aspergillus section Flavi, including Aspergillus flavus Link (Cotty et al 1994). Aflatoxins contaminate crops such as maize, peanut, cassava, sorghum, cottonseed, rice, wheat, chilies, and tree nuts (Essono et al 2009; Kachapulula et al.2017; Picot et al 2017; Probst et al 2007; Singh and Cotty 2019). Reduction in crop aflatoxin content by application of these atoxigenic A. flavus biocontrol products has been primarily attributed to competitive exclusion (Cotty and Bayman 1993, Mauro et al.2018, Senghor et al 2020). Community structure changes are driven by founder effects, competitive superiority of atoxigenic strains, advantages instilled by nutrients in the biopesticide formulation, and delivery of the product to the soil surface without incorporation into a trapping soil matrix
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