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Fungal diseases, beware!

Two yeasts have been pinpointed that produce killer toxins that block the growth of other yeasts.

The toxins, more properly known as antifungal cytotoxic proteins, could be good news for agriculture and food industries looking for new weapons to fight pests, diseases, and dangerous microorganisms.

ARS geneticists G. Thomas Hayman, Paul L. Bolen, and colleagues identified the yeasts as strains of Pichia inositovora and P. acaciae. Hayman is with ARS' National Center for Agricultural Utilization Research in Peoria, Illinois. Bolen is now with International Flavors and Fragrances, Union Beach, New Jersey.

The toxin from P. acaciae tackles a large number of yeasts while that from P. inositovora seems more specific, singling out just a few to attack.

"We call them killer toxins," Bolen says, "though that may be somewhat of a misnomer. We know that they prevent sensitive yeasts from growing, but we've yet to determine how this inhibition occurs. It may be that the toxins aren't actively involved in the killing process."

Patent applications are under way for both toxins. P. inositovora and P. acaciae have been deposited as NRRL Y-18709 and NRRL Y-18665, respectively, in the ARS Patent Culture Collection. Commercial use of the technology will be available for licensing from USDA.

The concept of using yeast toxins against unwanted yeasts isn't new. A toxin from another yeast, Kluyveromyces lactis, has already been put to work in fermenting sake, or rice wine. That yeast's toxin--harmless to humans and animals--keeps out unwanted yeasts that may contaminate the process.

Researchers think that the antifungal toxins from P. acaciae and P. inositovora are the products of genes carried on their linear plasmids--double-stranded pieces of DNA that are separate from the chromosome. Other genes appear to give each yeast immunity to its own toxin.

Linear plasmids occur also in molds and higher plants where they reside in mitochondria, the

cells' power plants. But in these yeast strains, the plasmids are found in the inner portion of the yeast cell known as the cytoplasm.

Bolen and several colleagues at Peoria earlier discovered linear plasmids in four strains of another yeast species. They were searching for plasmids that would aid the fermentation of xylose, a type of sugar.

Killer toxins from still other yeasts have been successful in treating fungal skin infections of experimental animals. The toxin from the P. acaciae strain might help fight mastitis, a fungal disease in cows; the most prevalent types of yeasts involved in this disease are sensitive to its toxin. However, the toxin's effect on mammals has yet to be determined.

In addition to producing toxins, these yeast strains and their linear plasmids promise to be important genetic engineering tools.

Scientists commonly use circular plasmids as vectors to move or shuttle genetic information from one organism to another. Pieces of linear plasmids can be inserted into a circular plasmid, enabling the circular plasmids to replicate more efficiently or in different host cells. Such plasmids would allow genes to be efficiently shuttled between different yeasts.

"Linear plasmids may themselves also work as vectors, though it may be more difficult to move them into other organisms," says Bolen.

"However, linear plasmids have a lot going for them. Unlike many circular plasmids, a single cell contains numerous copies of each linear plasmid, and they're extremely stable," Hayman says. "These two properties, high copy number and stability, may make them valuable genetic engineering tools."-- By Marcie Gerrietts, ARS.

G. Thomas Harman is in the USDA-ARS Biopolvmer Research Unit, National Center for Agricultural Utilization Research, 1815 N. University, Peoria, IL 61604. Phone (309)685-4011.

For patent licensing information, contact the ARS Patent Coordinator, Room 403, Bldg. 005, BARC-West, 10300 Baltimore Ave., Beltsville, MD 20705-2350. Phone (301) 504-6786.

World's Largest Collection of Molds, Yeasts, and Bacteria

Some of science's most valuable tools are tucked away in a dark room on the third floor of the National Center for Agricultural Utilization Research (NCAUR) at Peoria, Illinois.

One of the world's largest microbial culture collections, the ARS Culture Collection contains more than 80,000 specimens of yeasts, molds, and bacteria of agricultural and industrial importance. Specific cultures related to microbiological inventions are deposited in conjunction with U.S. patent

applications into the ARS Patent Culture Collection.

Since its establishment, the ARS Culture Collection has played a major role in the research on penicillin and other antibiotics, riboflavin, organic acids, xanthan and dextran gums, mycotoxins, and food fermentations.

Although the culture collection formally began when the Northern Regional Research Laboratory (now NCAUR) opened in 1940, Cletus Kurtzman, head of the collection, says that its origin can be traced back to 1904.

That's when Charles Thom joined USDA and began investigating Roquefort and Camembert cheeses. Thom and his assistant Margaret B. Church eventually acquired hundreds of mold cultures that became known as the Thom and Church collection.

The collection was deposited at the USDA facility at Peoria when Kenneth B. Raper, a colleague of Thom' s, became head of the culture collection-Additional molds, bacteria, and yeasts were also deposited in the collection when it was formally established.

"Other cultures have been added to the collection as they've been acquired by scientists in USDA and the private sector," says Kurtzman. "In some cases, entire collections that might otherwise have been lost to science because of retirements or changes in research programs have been accessioned."

Most of the specimens in the collection are freeze-dried and stored in glass ampules. Specimens are stored at about 40*F and can be revived even after half a century. Some, though, are damaged by freeze-drying and are instead frozen in liquid nitrogen to keep them viable.

In the last decade, efforts have concentrated on finding microorganisms to use in the conversion of biomass to ethanol. Current and future work will be closely aligned with biotechnology.

"Scientists are using microorganisms from the collection in research to fmd natural ways to combat weeds, insects, and fungal infections," says Kurtzman. "We're also looking for ways to use microorganisms for the production of specialized organic compounds from low-cost agricultural products."

Cultures from the general collection are provided free of charge to anyone involved with research and development. More than 4,000 specimens are requested annually, says Kurtzman.

Culture strains deposited in the ARS Patent Culture Collection are maintained for at least the 17-year life of a U.S. patent and for 30 or more years when deposited under an international agreement such as the Budapest Treaty. The depositor may make the microorganism freely available on deposit or opt to wait until the patent has been issued.--By Marcie Gerrietts, ARS.

Cletus P. Kurtzman is at the USDA-ARS Natianal Center for Agricultural Utilization Research, 1815 North University, Peoria, IL 61604. Phone (309) 685-4011, ext. 385.
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Title Annotation:includes related article on the Agricultural Research Service's microbial culture collection; antifungal cytotoxic protein research by geneticists G. Thomas Hayman, Paul L. Bolen and colleagues
Author:Gerrietts, Marcie
Publication:Agricultural Research
Date:Jun 1, 1992
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