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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR AND GENETIC APPROACHES TO SUPPRESSING FUNGAL PATHOGENS AND MYCOTOXIN CONTAMINATION

Location: Foodborne Toxin Detection and Prevention

2010 Annual Report


1a.Objectives (from AD-416)
Objectives of the research .
1)Release a promising insect resistant, premium quality almond variety, and evaluate other advanced breeding selections..
2)Characterize almond seed coat tannins at the genetic and biochemical levels and examine associaion of specific antioxidants with seed coat ink staining..
3)Identify and integrate multiple resistances into regionally adapted, high commercial quality breeding selections. Reduce mycotoxin contamination of agricultural commodities focusing on tree nuts (almonds, pistachios and walnuts) by identifying natural constituents or biocompetitive organisms that inhibit growth of fungi and aflatoxin production. Identify target genes in fungi that trigger mycotoxin biosynthesis focusing on stress response pathways.


1b.Approach (from AD-416)
Identify the natural constituents responsible for resistance of certain varieties of tree nuts to growth of aflatoxigenic strains of aspergillus. Isolate and identify novel metabolites in sclerotia of Aspergillus and develop analytical methods for such compounds in order to assess exposure levels of tree nut orchards to the fungus. Identify genes involved in triggering mycotoxin biosynthesis using high-through put bioassays. Assays involve use of deletion mutants, gene knockouts and complementation analysis. Discover natural compounds that disrupt functionality of gene targets identified. Develop biosensors for detecting toxic fungi in pre- and post harvest environments. Combining 5325-32000-006-00D (1/09).


3.Progress Report
PMR researchers have made significant progress on resolving the problem of mycotoxin contamination. This has come about mainly by the discovery of natural products affecting mycotoxigenesis and elucidation of the functional genomics behind toxin production and fungal development. The highlight of our research was the discovery that antioxidants inhibit aflatoxin biosynthesis. We found that antioxidants "tricked" the fungus into producing enzymes that are usually induced by oxidative stress, switching off the aflatoxin biosynthetic pathway. We found that regulation of aflatoxin biosynthesis had to be either directly or indirectly affected by genetic signaling pathways involving oxidative stress. So, we targeted these pathways as a means to control fungal development. We screened >60 compounds and found a number that are good agents against oxidative or osmotic stress pathways. We next discovered that these compounds could be used in combination with commercial antifungal agents to boost their effectiveness, so-called "chemosensitization." Treatment by these safe natural compounds disrupts the ability of the fungus to respond to stresses, such as treatment with fungicides or antifungal drugs. We expanded our research to include medically important, animal and human pathogenic fungi. We were able to show that we could make fungi that are resistant to antifungal agents, susceptible to them through chemosensitization. Both field and animal model experiments are underway using chemosensitization against plant pathogenic animal pathogenic fungi, respectively. Because of this progress, there is great promise that the efforts over the past few years can translate into implementation of control methodology.


4.Accomplishments
1. Safe natural products augment effectiveness of a commercial fungicides. One of the major fungal pests to the apple industry is a fungus called "blue mold" which causes apple rot in both the orchard and in storage and contamination by the toxin, patulin. The commercial fungicide, fludioxonil is commonly used to control this fungus, but strains of this fungus are beginning to show resistance to this fungicide. Researchers at the Plant Mycotoxin Research Unit in Albany, California discovered some safe, natural compounds that can be used to make these resistant strains of blue mold susceptible to this fungicide. This finding provides a method to improve effectiveness of commercial fungicides for controlling this fungus and helps the apple industry to improve apple quality for those who enjoy apples and apple products.

2. Effectiveness of antifungal drugs is improved by natural products. Fungi causing very serious invasive diseases of animals and humans are on the rise because of resistance to available antifungal drugs. In addition, these drugs are quite toxic and expensive. Researchers at the Plant Mycotoxin Research Unit in Albany, California have found a method whereby safe natural compounds can be used to augment activity of antifungal drugs and overcome resistance. If this method is found to be clinically effective it would be quite beneficial to both human medical and veterinarian medicine by overcoming resistance, reducing drug dosages, costs of treatment and dangerous side-effects of drug treatment.


5.Significant Activities that Support Special Target Populations
There are many fungal diseases that are mainly a problem with people who live in agrarian environments. The discovery of safe natural products that improve effectiveness of antifungal drugs can be quite helpful in the chemotherapeutic treatment of these diseases. This discovery by PMR scientists could have an impact on people who live in rural environments.


Review Publications
Mcgarvey, J.A., Miller, W.G., Lathrop, J.R., Silva, C.J., Bullard, G. 2009. Induction of Purple Sulfur Bacterial Growth in Dairy Wastewater Lagoons by Circulation. Letters in Applied Microbiology. 49:427-433.

Janagama, H.K., Senthilkumar, T., Bannantine, J.P., Rodriquez, M.G., Smith, I., Paustian, M.L., Mcgarvey, J.A., Sreevatsan, S. 2009. Identification and Functional Characterization of the Iron Dependent Regulator (IdeR) of Mycobacterium avium subspecies paratuberculosis. Microbiology. 155:3683-3690.

Mcgarvey, J.A., Hamilton, S., Depeters, E., Mitloehner, F. 2010. Effect of dietary monensin on the bacterial population structure of dairy cattle colonic contents. Applied Microbiology and Biotechnology. 85:1947-1952.

Mahoney, N.E., Molyneux, R., Kim, J.H., Campbell, B.C., Waiss, A.C., Hagerman, A.E. 2010. Aflatoxigenesis induced in Aspergillus flavus by oxidative stress and reduction by phenolic antioxidants from tree nuts. World Mycotoxin Journal. 3(1):49-57.

Kim, J.H., Campbell, B.C., Mahoney, N.E., Chan, K.L., Molyneux, R.J., Xiao, C. 2010. Use of chemosensitization to overcome fludioxonil-resistance in Penicillium expansum. Letters Appl. Microbiol. DOI: 10.1111/j.1472-765X

Last Modified: 8/22/2014
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