Genetic responses and aflatoxin inhibition during co-culture of aflatoxigenic and non-aflatoxigenic Aspergillus flavus
Sweany, Rebecca R. | Mack, Brian M. | Moore, Geromy G. | Gilbert, Matthew K. | Cary, Jeffrey W. | Lebar, Matthew D. | Rajasekaran, Kanniah | Damann, Kenneth E. Jr
Aflatoxin is a carcinogenic mycotoxin produced by Aspergillus flavus. Non-aflatoxigenic (Non-tox) A. flavus isolates are deployed in corn fields as biocontrol because they substantially reduce af-latoxin contamination via direct replacement and additionally via direct contact or touch with toxigenic (Tox) isolates and secretion of inhibitory/degradative chemicals. To understand touch inhibition, aflatoxin analysis and RNA-seq examined gene expression of Non-tox isolate 17 and Tox isolate 53 monocultures and during their interaction in co-culture. Fewer than expected unique reads were assigned to Tox 53 during co-culture, indicating its growth and/or gene ex-pression was inhibited in response to Non-tox 17. Aflatoxin production was reduced by 99.7% in 72 h co-cultures. Hundreds of predicted secreted proteins and genes involved in oxida-tion/reduction were enriched in Non-tox 17 and co-cultures compared to Tox 53. Five secondary metabolite (SM) gene clusters and kojic acid synthesis genes were upregulated in Non-tox 17 compared to Tox 53 and a few were further upregulated in co-cultures in response to touch. These results suggest Non-tox strains can inhibit growth and aflatoxin gene cluster expression in Tox strains through touch. Additionally, upregulation of other SM genes and redox genes during the biocontrol interaction demonstrates a potential role of inhibitory SMs and antioxidants as addi-tional biocontrol mechanisms and deserves further exploration to improve biocontrol formula-tions.
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