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United States Department of Agriculture

Agricultural Research Service


Location: Food and Feed Safety Research

2009 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
Several new investigations have begun with plant compounds that are commercially available that might control or inhibit microbial pests. These include trans-2-hexenal and trans-2-heptenal, which are produced by soybeans. Also studied was bisabolol (from chamomile oil) and dragosantol, the synthetic form of bisabolol. These compounds were tested in laboratory assays against a panel of species from the fungal genera of Aspergillus, Fusarium, Cladosporium, Trichoderma, and Colletrotrichum. For comparison, we also tested these compounds against the bacteria Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus antrophaeus. The soybean compound showed adequate fungicidal and bactericidal activity. However, bisabolol and dragosantol displayed excellent activity against these microbes.

Under an arrangement with Symrise, a producer of plant compounds for the cosmetics industry, bisabolol and dragosantol were obtained. We have begun initial studies using a bench top “model grain silo” to study the ability of soybean derived compounds, bisabolol, and dragosantol to stop Aspergillus flavus from growing on wetted corn. To date, we have shown that trans-2-hexenal kills A. flavus growth in this model. Future work will study the remaining compounds in this model.

Collaborative work with Utah State University was completed showing that rhamnolipid, a detergent, enhances the fungicidal properties of the bacterial peptide, syringomycin-E, against primary and secondary pathogens of grapes that were isolated from diseased grapes in a local vineyard.

Four Small Business Innovative Research (SBIR) grants were co-authored with Sensor Development Corporation, which is developing real-time electronic sensors for Aspergillus flavus growth in contaminated corn. This is a long-term project to identify and quantitate the volatile compounds produced by this fungus on wetted corn under conditions which approximates those in silos where corn gets wet, thereby allowing fungi to grow. We have identified the five volatile compounds that are most prevalent when these fungi are growing on corn. The company is developing a sensor based on these identifications.

1. In vitro fungicidal properties of trans-2-hexenal and trans-2-heptenal: Earlier studies in our group identified these compounds as produced by soybeans and that they had fungistatic properties when A. flavus was grown on corn. During FY 2009, we showed that, in laboratory assays, these compounds have a moderate level of fungicidal property against several species of Aspergillus and Fusarium, as well as species of Collectotrichum and Curvularia. They also had moderate bactericidal properties against Pseudomonas aeruginosa and Staphylococcus aureus. The data shows that these soybean-produced compounds have fungicidal and bactericidal properties.

2. Fungicidal properties of bisabolol and dragosantol: Bisabolol is a chemical (alcohol) that is made-up of 15 carbon chain present in chamomile oil, while dragosantol is the synthetic version of bisabolol. Both are inexpensive, commercially available, used in cosmetics, and are considered Generally Considered as Safe (GRAS). Our assays show both to be potent fungicides against species of Aspergillus, Fusarium, Colletotrichum, and Cladosporium. We also observed bactericidal activity against Pseudomonas aeruginosa and Staphylococcus aureus. Future plans are to test these volatiles compounds in our model grain silo to determine efficacy against A. flavus and F. graminearum.

3. Enhanced fungicidal properties of syringomycin-E and rhamnolipid: Syringomycin-E, a peptide produced by the bacterium, Pseudomonas syringae, was determined in our lab in the past to be a potent fungicide against species of Aspergillus and Fusarium in earlier experiments. In FY 2009, we determined that this peptide, supplied by Utah State University, when combined with rhamnolipid, a microbially-produced detergent, was superior as a fungicide to syringomcin-E alone against Greeneria uvicola, a primary pathogen of grapes, and a number of fungi known to be opportunistic grape pathogens.

4. Identification of volatile compounds produced by Aspergillus flavus on corn: Extensive testing determined the predominant volatile compounds produced by toxigenic and non-toxigenic isolates of Aspergillus flavus. This work is being performed with the Cooperator. Based on our data, SDC is developing a real-time electronic sensor to detect A. flavus growth, and subsequent aflatoxin production, in stored corn. SDC will patent this instrument and sell it to companies concerned with aflatoxin contamination of stored grains. We plan similar work in future years to detect Fusarium growth on stored grain. We also believe that this data could lead to the development by SDC of an instrument for the detection of fungal pulmonary infections, which have a high mortality (80% or greater). If successful, these instruments installed in grain storage facilities and hospitals will save many millions of dollars of stored grains, help insure the safety of the grain supply from fungal rot and toxins formation, as well as millions of dollars for treatment of patients with pulmonary mycoses and the saving of many lives.

6.Technology Transfer

Number of Active CRADAs1
Number of Invention Disclosures Submitted1
Number of Other Technology Transfer4

Review Publications
Cleveland, T.E., Carter Wientjes, C.H., De Lucca II, A.J., Boue, S.M. 2009. Effect of soybean volatile compounds on Aspergillus flavus growth and aflatoxin production. Journal of Food Science. 74(2):H83-H87.

Last Modified: 9/10/2014
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