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theses

Mycotoxins are fungal secondary metabolites that contaminate global food supplies by infecting pre- and post-harvest crops. Contaminated foods are highly hazardous to human health and cause economic losses to agricultural and food industries. Control of mycotoxin accumulation generally involves prevention such as use of chemical and biological agents to inhibit growth of toxigenic fungal strains. Two well-known toxins, patulin and aflatoxin, are among the most harmful compounds produced respectively by the fungi Penicillium expansum and Aspergillus flavus. Using molecular and computational methods, I investigated the biological mechanisms by which volatile 1-octen-3-ol affects patulin production by P. expansum and how genetic differences among non-aflatoxigenic A. flavus strains affect biocontrol effectiveness. My results demonstrate that exogenous volatile 1-octen-3-ol increases patulin production on a medium that normally suppresses biosynthesis of the mycotoxin. This increase correlates with an increased expression of a glucose oxidase gene and differential expression of thirty other genes involved in membrane transport, oxidation-reduction and carbohydrate metabolism. I compared the genomes and transcriptomes of two non-aflatoxigenic strains that are good or poor at biocontrol against aflatoxins to other sequenced A. flavus strains. The former contains an enriched number of genes predicted to be involved in oxidation-reduction processes that were not found in other inspected A. flavus strains. The non-aflatoxigenic strain that is a poor biocontrol agent has increased relative expression of six genes involved in stress response, which may help explain why the strain grows more slowly than other tested strains. A common theme that emerged from my studies on the genomes and transcriptomes of P. expansum and A. flavus was the identification of putative oxidation-reduction genes, indicating an important role of redox reactions in mycotoxin production. Overall, I obtained evidence for how 1-octen-3-ol induces patulin production and how high expression of stress response genes might impede competitive growth for aflatoxin biocontrol. It is my hope that this research will contribute to our general understanding of how volatile signaling and gene expression influence mycotoxin production and accumulation.

ETD_9711

Ph.D.

Includes bibliographical references

doi:10.7282/t3-xrgn-d904

ETD doctoral

The author owns the copyright to this work.