Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2012
Publication Date: 1/12/2012
Citation: Chang, P.-K., Abbas, H.K., Weaver, M.A., Ehrlich, K., Scharfenstein, L.L., Cotty, P.J. 2012. Identification of genetic defects in the atoxigenic biocontrol strain Aspergillus flavus K49 reveals the presence of a competitive recombinant group in field populations. International Journal of Food Microbiology. 154:192-196.
Interpretive Summary: Contamination of crops by aflatoxin represents a significant global risk to human and animal health and can cause devastating economic losses due to strict regulatory limits placed on dissemination of contaminated products. Cyclopiazonic acid (CPA) is a neurotoxin that often co-contaminates crops. A strategy showing great promise in preventing preharvest mycotoxin contamination of susceptible crops is the introduction of non-aflatoxigenic A. flavus strains to competitively displace toxigenic aspergilli. In this study, we identified the genetic defects underlying the lack of production of aflatoxin and CPA by a prospective biocontrol strain, Aspergillus flavus K49 currently being tested in Mississippi corn fields. The work reveals that K49 and the proven biocontrol strain A. flavus AF36 currently being applied in Arizona, Texas and California have a shared phylogeny and that certain unique genetic polymorphisms allow for future selection of promising biocontrol strain candidates.
Technical Abstract: Contamination of corn, cotton, peanuts and tree nuts by aflatoxins is a severe economic burden for growers. A current biocontrol strategy is to use non-aflatoxigenic Aspergillus flavus strains to competitively exclude field toxigenic Aspergillus species. Aspergillus flavus K49 does not produce aflatoxins and cyclopiazonic acid (CPA) and is currently being tested in corn-growing fields in Mississippi. We found that its lack of production of aflatoxins and CPA resulted from single nucleotide mutations in the polyketide synthase gene and hybrid polyketide-nonribosomal peptide synthase gene, respectively. Furthermore, based on single nucleotide polymorphisms of the aflatoxin biosynthesis omtA gene and the CPA biosynthesis dmaT gene, we conclude that K49, AF36 and previously characterized TX9-8 form a biocontrol group. These isolates appear to be derived from recombinants of typical large and small sclerotial morphotype strains. This finding provides an easy way to select future biocontrol strains from the reservoir of non-aflatoxigenic populations in agricultural fields.