Effects of temperature and medium composition on inhibitory activities of gossypol-related compounds against aflatoxigenic fungi

Authors: Mellon, Jay; Dowd, Michael; Beltz, Shannon

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2013
Publication Date: 6/13/2013
Citation: Mellon, J.E., Dowd, M.K., Beltz, S.B. 2013. Effects of temperature and medium composition on inhibitory activities of gossypol-related compounds against aflatoxigenic fungi. Journal of Applied Microbiology. 115:179-186.

Interpretive Summary: Aflatoxin is a very potent carcinogen and toxin that is produced by the fungi Aspergillus flavus and A. parasiticus. When these fungi infect oilseed crops, the developing seed can become contaminated with this toxin, rendering the product unusable for food or feed. Cotton plants contain high levels of gossypol that provides protection against insect predation and possibly additional defense functions. Gossypolone is an oxidative derivative of gossypol formed in animal systems (e.g. liver detoxification); apogossypolone is another oxidative derivative of gossypol. An investigation was undertaken to determine effects of temperature and media composition on the inhibitory activities displayed by these gossypol-related compounds against aflatoxigenic fungi. Increased incubation temperature marginally increased growth inhibition expressed by these compounds, but reduced the aflatoxin inhibition of gossypol. Gossypolone and apogossypolone retained good aflatoxin inhibitory activity at higher temperatures. Fungal growth in rich media greatly reduced growth inhibition of these compounds compared to minimal medium. Apogossypolone expressed strong aflatoxin inhibition in minimal medium, but this activity was significantly reduced in rich media. Incubation temperature and medium composition do affect the potency of growth and aflatoxin inhibition displayed by these compounds against aflatoxigenic fungi. This research will benefit oilseed breeders, producers and pathologists, and will aid in the formulation of methods to prevent aflatoxin contamination of food and feedstuffs.

Technical Abstract: Effects of temperature and medium composition on growth/aflatoxin inhibitory activities of gossypol, gossypolone and apogossypolone against Aspergillus flavus and A. parasiticus were investigated. The compounds were tested in a Czapek agar medium at 25 C, 31 C and 37 C at a concentration of 100 µg per mL. These same terpenoids were compared in Czapek Dox, Czapek with a protein/amino acid addendum and yeast extract-sucrose (YES) media at 100 µg per mL for growth and aflatoxin inhibitory activities against the above aflatoxigenic fungi. Increased incubation temperature marginally increased growth inhibitory activity of these compounds, but reduced the aflatoxin inhibitory activity of gossypol. Gossypolone and apogossypolone retained good aflatoxin inhibitory activity against A. flavus and A. parasiticus at the higher incubation temperatures. However, increased temperatures significantly reduced aflatoxin production in control cultures. Growth of these fungi in a minimal medium (Czapek Dox) containing a protein addendum or in a comparatively rich medium (YES) greatly reduced growth inhibitory activities of these terpenoids. Apogossypolone displayed strong anti-aflatoxigenic activity in the minimal medium, but this activity was significantly reduced in the protein-amended or rich medium. Interestingly, gossypol, which displayed little to no aflatoxin inhibitory activity in the minimal medium, did yield significant anti-aflatoxigenic activity in the YES medium. Incubation temperature and media composition appear to be important parameters involved in the regulation of aflatoxin production in A. flavus and A. parasiticus. In addition, these parameters also affect the potency of growth and aflatoxin inhibitory activities of these gossypol-related compounds against aflatoxigenic fungi.