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United States Department of Agriculture

Agricultural Research Service

Research Project: DISCOVERY OF ANTIFUNGAL COMPOUNDS FROM LOW VALUE/UNDERUTILIZED CROPS AND CROP CO-PRODUCTS
2010 Annual Report


1a.Objectives (from AD-416)
Enhance value and utilization of low value/underutilized crops and crop co-products through discovery and purification of novel, constituent antifungal compounds and determine commercial potential of discovered antifungals.


1b.Approach (from AD-416)
Barley and cotton 3-day old cotyledons will be extracted aqueously, as will okra fruit, and peanut and rice hulls. Filtered, freeze-dried extracts will be tested for fungicidal properties. Active compounds will be purified by HPLC/MS and activity monitored with bioassays using Aspergillus flavus and Fusarium oxysporum. NMR will determine chemical structure of antifungal compounds. Novel compounds will be patented and all active compounds will be tested for their antifungal spectra of activity. Commercial potential of compounds as agricultural fungicides and medical antifungals will be determined by collaborators. Discovered protein antifungals will be cloned. Construct genes will be incorporated into gene expression systems to obtain a protective effect against fungal pathogens.


3.Progress Report
This report documents progress for the parent Project 6435-41000-101-00D Discovery of Antifungal Compounds from Low Value/Underutilized Crops And Crop Co-Products that started in October 2009 and continues research from Project 6345-41000-097-OOD of the same title.

Research on the fungicidal properties of certain soybean volatile compounds, e.g., trans-2-hexenal and trans-2-heptenal, was expanded. Our data showed that, in the volatile state, trans-2-hexenal was superior to trans-2-heptenal volatiles, in preventing Aspergillus flavus growth and aflatoxin (a potent fungally produced carcinogen on crops) production. Even after the pumped trans-2-hexenal ceases to flow, the corn displayed no Aspergillus flavus growth, suggesting that the fungus was killed, not simply inhibited from growing.

Under a Confidentiality Agreement with our stakeholder, Symrise (producer of bisabolol and dragosantol), we expanded our studies of the antimicrobial spectrum of activity of these two compounds known as terpenes. Bisabolol is found in plant oils (e.g., chamomile oil), while dragosantol is the synthetic version of bisabolol. Both are antimicrobial, but are safe for human use. Our attempts to volatilize both compounds for studies in our wet corn/Aspergillus flavus assays (see above) were only partially successful. In future work, we need to develop a better protocol for volatilizing these compounds.

We continued our non-funded research, begun in FY-2009, on the antimicrobial properties of wheat histones (proteins associated with deoxyribonucleic acid) provided to us by our collaborator (University of Lund, Sweden). We found that these histones are highly active against many, but not all fungi. The collaborator’s data suggests that the membrane composition of different species is most likely due to the different sensitivity we see for different microbial genera.

In recent years, the scientific literature has described the use of visible light to kill microorganisms. We began exploratory experiments to determine whether blue light (470nm) could kill several different harmful bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus atrophaeus, Leuconostoc mesenteroides) and fungi (Aspergillus flavus, Fusarium verticillioides). The light, alone, kills all the bacteria, but not the fungi. However, blue light in combination with photosensitizing compounds kill fungi.

Our research on determining the secondary metabolic volatiles produced only by toxigenic strains of Aspergillus flavus continues. During FY2010, we reported to our stakeholder, Sensor Development Corporation, the identities of such compounds. Based on our data, the company has developed a “second generation” prototype real-time electronic sensor that will soon undergo Beta testing in grain silos.


4.Accomplishments
1. Identification of Secondary Metabolic Volatile Compounds Unique for Toxigenic Aspergillus flavus Grown on Corn. Stored corn can be contaminated by aflatoxin, a cancer-causing compound produced by Aspergillus flavus, when corn becomes wet. Aflatoxin is dangerous to humans and animals and, each year, costs United States Agriculture many millions of dollars in contaminated corn and other oilseeds. Current detection of this toxin requires extensive, time-consuming testing of corn in a laboratory. A real-time sensor, dedicated to detect Aspergillus flavus growth, would immediately warn grain handlers of contaminated grain and reduce the need for aflatoxin testing in laboratories. Agricultural Research Service researchers (Food and Feed Safety Research Unit, Southern Regional Research Center, New Orleans, LA) successfully determined the identity of secondary metabolic volatiles specific for aflatoxin-producing strains of Aspergillus flavus when grown on sterile, wet cracked corn. Our stakeholder, Sensor Development Corporation, has used our data to develop a “second-generation” prototype sensor using proprietary electronic chips and mathematical algorithm soon to undergo Beta testing in grain silos. The impact is improved prototype sensor for the detection of aflatoxigenic Aspergillus flavus growing in corn.


Review Publications
Le Blanc, B.W., Davis, O.K., Boue, S., Delucca, A., Deeby, T.A. 2009. Antioxidant Activity of Sonoran Desert Bee Pollen. Journal of Agricultural and Food Chemistry. 115, 1299-1305.

Rajasekaran, K., De Lucca II, A.J., Cary, J.W. 2009. Aflatoxin control through transgenic approaches. Toxin Reviews. 28(2):89-101.

Cornelius, M.L., Lyn, M.E., Williams, K.R., Lovisa, M.P., De Lucca II, A.J., Lax, A.R. 2009. The efficacy of bait supplements for improving the rate of discovery of bait stations in the field by the formosan subterranean termite (Isoptera: Rhinotermitidae). Journal of Economic Entomology. 102(3):1175-1181.

Last Modified: 10/20/2014
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