Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2011
Publication Date: 8/15/2011
Citation: Baidyal, S., Cary, J.W., Grayburn, S., Calvo, A.M. 2011. Role of nitric oxide and flavohemoglobin homolog genes in Aspergillus nidulans sexual development and mycotoxin production. Applied and Environmental Microbiology. 77(15):5524-5528. Interpretive Summary: This work describes experiments that have been conducted in an effort to better understand the mechanisms by which aflatoxins are produced by fungi. Aflatoxins are toxic and carcinogenic compounds often produced by the fungi, Aspergillus flavus and Aspergillus parasiticus, during growth on crops such as corn, peanuts, cottonseed, and treenuts. Because of the potential health risks, aflatoxin contamination of food and feed crops is also of great economic importance to farmers who cannot sell their crops due to strict domestic and international regulatory guidelines with regards to aflatoxin contamination. Studies have shown that just about all organisms produce a small gaseous molecule, nitric oxide (NO) that is involved in many biological processes including development and response to stress. To study the effect of NO on growth of the model fungus, Aspergillus nidulans, we developed a strain that no longer makes an enzyme termed flavohaemoglobin that is used by the fungus to breakdown NO that it generates during growth. These strains showed reduced production of sterigmatocystin, a precursor to aflatoxin, as well as a propensity to develop sexually. This strain will allow us to continue to unravel the mechanisms responsible for production of aflatoxin and development in Aspergillus which in turn will help in development of strategies for eliminating aflatoxin contamination of food and feed crops.
Technical Abstract: Flavohemoglobins are widely distributed proteins in both prokaryotic and eukaryotic organisms, conferring resistance against nitrosative stress. In the present study we investigated the role of two flavohemoglobin homologous genes, fhbA and fhbB, in morphogenesis and in the production of the mycotoxin sterigmatocystin in Aspergillus nidulans. Deletion of fhbA induced sexual development and decreased sterigmatocystin production. Supplementation of A. nidulans cultures with a nitric oxide-releasing compound increased cleistothecial formation. This coincided with higher expression of the sexual development regulatory genes nsdD and steA, indicating that nitric oxide is an inducer of fungal sexual development. This is the first study on the effect of nitric oxide on morphogenesis and secondary metabolism in fungi.