Submitted to: International Journal of Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2006
Publication Date: 2/15/2007
Citation: Chang, P.-K., Hua, S.S.T. 2007. Nonaflatoxigenic Aspergillus flavus TX9-8 Competitively Prevents Aflatoxin Accumulation by A. flavus Isolates of Large and Small Sclerotial Morphotypes. International Journal of Food Microbiology. 114:275-279. Interpretive Summary: Aflatoxins are toxic and carcinogenic contaminants of foods and feeds. Several aflatoxin non-producing strains of Aspergillus flavus are currently being tested as biological control agents to manage aflatoxin contamination of cotton, corn, and tree nuts in the field. The A. flavus population is diverse. In this study, the ability of nonaflatoxigenic A. flavus isolates from three previously categorized subgroups to interfere with aflatoxin production of toxigenic A. flavus isolates was examined. From one subgroup, a good competitor, A. flavus TX9-8, which has a defect in the polyketide synthase gene was identified. Simultaneous co-inoculation of TX9-8 with large sclerotial A. flavus isolates prevented aflatoxin accumulation. TX9-8 also decreased aflatoxin accumulation of small sclerotial A. flavus isolate significantly. TX9-8 may be used together with other nonaflatoxigenic A. flavus strains to represent a range of “stacked” competitors to outgrow toxigenic A. flavus isolates and prevent aflatoxin contamination of agricultural commodities.
Technical Abstract: Aflatoxins are a family of highly toxic and carcinogenic toxins produced by several Aspergillus species. Aflatoxin contamination of agricultural commodities, both pre- and post-harvest, is a serious food safety issue and a significant economic concern. Using aflatoxin non-producing A. flavus isolates to competitively exclude toxigenic A. flavus isolates in agricultural fields has become an adopted approach to reduce aflatoxin contamination. From screening subgroups of nonaflatoxigenic A. flavus, we identified an A. flavus isolate, TX9-8, which competed well with three A. flavus isolates producing low, intermediate, and high levels of aflatoxins, respectively. TX9-8 has a defective polyketide synthase gene (pksA), which is necessary for aflatoxin biosynthesis. Co-inoculating TX9-8 at the same time with large sclerotial (L strain) A. flavus isolates at a ratio of 1:1 or 1:10 (TX9-8:toxigenic) prevented aflatoxin accumulation. The intervention of TX9-8 on small sclerotial (S strain) A. flavus isolates varied and depended on isolate and ratio of coinoculation. At a ratio of 1:1, TX9-8 prevented aflatoxin accumulation by A. flavus CA28 and reduced aflatoxin accumulation 10-fold by A. flavus CA43. No decrease in aflatoxin accumulation was apparent when TX9-8 was inoculated 24 hours after toxigenic L- or S strain A. flavus isolates started growing. The competitive effect likely is due to TX9-8 outgrowing toxigenic A. flavus isolates.