Environmental Science and Technology Online:
January 1, 2007
Vol. 41, Iss. 1
Science News –
January 10, 2007
Pfiesteria toxin identified
After nearly a decade of work, researchers have discovered a toxin produced by the dinoflagellate Pfiesteria piscicida.
Something in the water killed billions of fish in eastern U.S. estuaries throughout the 1990s. When a group of scientists blamed the kills on blooms of the dinoflagellate Pfiesteria piscicida, they wrote the beginning to a detective story that would spawn bitter debate over the next 15 years
Major kill of juvenile menhaden –
the fish most commonly affected
by Pfiesteria – in North Carolina's
Neuse River estuary.
Now, a key piece of evidence has emerged that could help bring an end to the controversy. In research published today on ES&T’s Research ASAP website (DOI: 10.1021/es0612605), a team of chemists and toxicologists led by Peter Moeller of the National Oceanographic and Atmospheric Administration (NOAA) describe a newly identified ephemeral toxin produced by Pfiesteria. The key to its elusiveness over the past decade, they say, is that the toxin is produced rapidly and then vanishes quickly upon exposure to sunlight and other environmental cues.
“We would observe toxic activity, and then it would disappear,” says Moeller, who spent more than 7 years characterizing the toxin using advanced analytical techniques. In the end, he resorted to working under red lights in the lab to keep the purified toxin stable long enough to study it.
During the peak of the crisis, a group of scientists led by JoAnn Burkholder of North Carolina State University described several species of the genus Pfiesteria. Burkholder published numerous papers on the high toxicity of Pfiesteria. State agencies scrambled to fund Pfiesteria monitoring projects, and the horrified public looked at fish covered in bloody lesions and wondered what the so-called “cell from hell” would do to swimmers and fishers. The scare cost the seafood industry about $43 million in revenues after one episode in Maryland alone, according to estimates by Doug Lipton of the University of Maryland. Burkholder’s work, and her conflicts with industry and other scientists even spawned a popular book, And the Waters Turned to Blood.
Over the years, other groups published papers saying that Pfiesteria wasn’t toxic at all. It was a parasitic fungus, or even just plain-Jane hypoxia, they said, that killed the fish. Or if it was Pfiesteria, it wasn’t toxic; it was the animal-like algae’s proclivity for feeding on fish skin. The oft-cited missing link was the lack of an identified toxin.
Meanwhile, the fish kills stopped after 1999. Burkholder attributes this change to the algae’s sensitivity to sediment disturbance from hurricanes such as that year’s Hurricane Fran. The uproar that had been dubbed “Pfiesteria hysteria” started to look more like “Pfiesteria fizzle”. But debate continued within the scientific community even as the mainstream news media lost interest.
Now, Burkholder says the identification of the toxin will allow research to move forward. “It’s like having a smoking gun,” she says.
The key to identifying the toxin lay in knowing what to look for. David Newman, chief of the natural products branch at the National Cancer Institute, provided an insight based on his 40 years of experience working with natural compounds. Moeller described to Newman the ephemeral nature of the toxin, noting that “it was only stable for a short time and relatively water soluble,” says Newman. “And I asked him if he had ever thought about a metallated [metal-containing] toxin.” In the end, Moeller’s group identified congeners of the toxin that contain iron and copper. The molecules produce free radicals, which act “like a molecular welding torch” to wreak cellular havoc, Newman says.
However, Moeller is careful regarding direct links between the toxin and fish kills. He purified the toxin for toxicological studies with Burkholder before it was fully characterized. “The confirmation of a toxin found as reported in this paper is that we have wild samples that are identical to our culture, so there’s good evidence that it’s the same toxin that killed fish. Now we have to go out into a wild bloom and identify it,” Moeller says.
Others go further. “It may be toxic, but in order to kill billions of fish, there’s got to be an awful lot of it and it’s got to stick around long enough to kill the fish,” says Robert Gawley of the University of Arkansas. Moeller acknowledges the short lifetime but says that free radicals are produced in large quantities and can act rapidly on cells.
“It’s what everyone has been waiting for—the characterization of a toxin. It could open up new avenues of research and resolve many of the issues that remain, and many of the controversies,” says Wolfgang Vogelbein of the Virginia Institute of Marine Science. In 2002, Vogelbein published research on Pfiesteria’s toxicity in feeding behavior in Nature and on its Proceedings of the National Academy of Sciences. Both papers questioned the existence of toxigenic Pfiesteria species. The environmental relevance of the newly described toxin will need to be tested next, he says.
Moeller hopes that others will work to understand how the toxin behaves in the environment. He notes that the toxic strain he used is available to other researchers in a culture collection.
This is probably not the last time Pfiesteria will make the news. Toxicologist Andrew Gordon of Old Dominion University sums it up nicely. “I don’t think the controversy is solved by this publication, but it gives us a paper tiger to test,” he says.—ERIKA ENGELHAUPT