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Researchers identify fungal inhibitor

A key bacterial compound that inhibits the growth of the plant pathogen Fusarium verticillioides has been identified by Agricultural Research Service (ARS) scientists. The compound could help protect plants, livestock and poultry from fusarium infection.

The compound is produced by Bacillus mojavensis strain RRC101. Finding better controls for F. verticillioides is important because fumonisin mycotoxins — especially fumonisin B1 — are toxic to livestock and poultry.

Microbiologist and research leader Charles Bacon and his team at the ARS Toxicology and Mycotoxin Research Unit in Athens, Ga., identified Leu7-surfactin as the inhibiting compound that controls F. verticillioides. The research team includes microbiologist Dorothy Hinton, chemist Maurice Snook and technician Trevor Mitchell. Their study was published in the April 2009 issue of the Journal of Agricultural and Food Chemistry.

B. mojavensis is a plant-residing bacterium that can be used to control fungal diseases in corn and other plants. Though B. mojavensis is known to work as a biocontrol agent, the specific substance responsible for inhibition of Fusarium was not identified until recently.

The Leu7-surfactin was isolated from growing the bacterium in liquid cultures. In lab tests, the compound proved effective in inhibiting growth of the fungus. Surfactin has a detergent-like activity that dissolves the lipid membranes inside the fungus, eventually killing it.

In Bacon's tests, Leu7-surfactin was effective at controlling F. verticillioides at very low concentrations of 20 micrograms per liter of liquid, making it more efficient to use. In addition to its antibiotic effects, surfactin can be used in textile manufacturing, environmental remediation, and fossil fuel recovery. This compound's properties create great potential for biotechnological and biopharmaceutical applications.

Bacon and his colleagues examined all currently available strains of B. mojavensis and found that all of the strains are endophytic-living within the plant-and all were active against F. verticillioides and other fungi in lab tests. The genus Bacillus is known for the production of more than 24 antibiotics, several of which are fungicidal with the potential to control plant diseases.

ARS is the principal intramural scientific research agency of the U.S. Department of Agriculture.

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