Scientists Successfully Isolate Fish-Killing Organism Pfiesteria Toxin In Lab Tests

In a series of experiments completed earlier this month, researchers at North Carolina State University, working in collaboration with the National Institute of Environmental Health Sciences (NIEHS) and the Marine Biotoxins Center at the National Marine Fisheries Service (NMFS), have for the first time successfully isolated and purified a water-soluble toxin component from Pfiesteria.

Isolating the toxin component makes it possible for scientists to complete the task of identifying its chemical structure, so they can develop accurate tests to detect its presence in fish, humans or other mammals who may have been affected.

"We expect to have the chemical identity of the toxin very shortly," says lead researcher Dr. JoAnn Burkholder, associate professor of aqautic botany at NC State.

The toxin component isolated by the researchers is unlike any other known dinoflagellate toxin, Burkholder says. "It has a different mode of action and acts more rapidly than any we have previously seen. It also appears to be heat stable. In repeated tests conducted during one phase of the isolation procedure, we heated the toxin to 170 degrees Fahrenheit for two hours and it remained potent," she says. "And it's highly lethal to fish. When exposed to its purified form, fish became moribund in two to three seconds and died within three minutes."

Tests also showed the toxin can damage mammalian neurological and pituitary cells. More testing is now under way to better understand the severity and duration of that damage.

Burkholder presented the findings of the collaborative research in an invited talk this morning (Tuesday, Aug. 26) at the NIEHS Workshop on Hazardous Marine/Freshwater Microbes and Toxins, in Research Triangle Park. Leading environmental scientists from the United States and Canada are taking part in the two-day workshop.

Burkholder and her colleagues at NIEHS and NMFS also have developed a promising new method for testing the toxicity of water collected at the scene of fish kills and related disease events. The method is called a reporter gene assay. It can quickly and reliably detect the presence of toxins -- even very low levels of them -- in water samples. The assay has been successfully tested in the lab. Months of field testing will now begin. "This assay will give researchers a much more concrete and accurate measurement method," Burkholder says.

Pfiesteria piscicida and other Pfiesteria-like species are predatory, single-celled aquatic dinoflagellates found in coastal estuaries from Delaware to Alabama. At least four Pfiesteria-like dinoflagellates are currently known; Burkholder has found at least two of them in North Carolina's estuaries. Of the four, only P. piscicida has yet been given a formal scientific name.

P. piscicida was first characterized and identified at the site of a fish kill in 1991 by Burkholder. (Burkholder's identification of the species was confirmed in independent tests by Dr. Karen Steidinger of the Florida Marine Research Institute in St. Petersburg, Fla.) Since 1991, P. piscicida has killed tens of millions of fish in North Carolina's shallow, nutrient-rich coastal waters. This year, Pfiesteria-like species also have been implicated in a fish kill on the Pocomoke River in Maryland. In some cases, Pfiesteria's toxins have been linked to human illnesses.

Widely acknowledged as the world's leading expert on Pfiesteria-like dinoflagellates, Burkholder has published 17 peer-reviewed scientific studies on Pfiesteria-like species. Earlier this year, she received a prestigious Pew Fellowship in Conservation and the Environment in recognition of her research and educational outreach.

The tests to isolate the Pfiesteria toxin were first conducted earlier this month by NC State and NIEHS researchers at NIEHS laboratories in Research Triangle Park. As a safeguard against error, the tests were repeated at NMFS, in Charleston, S.C. Results from the two sets of tests were consistent.

Researchers collaborating on the experiments included: Burkholder, Howard Glasgow and Nora Deemer from NC State; Dr. Frank Johnson and Dr. Michael Snell from NIEHS; and Dr. John Ramsdell, Dr. Peter Moeller, Stewart Edmunds and Elizabeth Fairey from NMFS.

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This release also is available on the NC State News Services Website at http://www2.ncsu.edu/ncsu/univ_relations/releases/current.html. For more information on Pfiesteria piscicida, or an on-line version of the research abstract (available later this week), check out Dr. JoAnn Burkholder's Website at http://www2.ncsu.edu/unity/lockers/project/aquatic_botany.