News of the Week

Is Sugary Toxin the Smoking Gun?

Science  01 Nov 2002:
Vol. 298, Issue 5595, pp. 945b-946b
DOI: 10.1126/science.298.5595.945b

A team of researchers claims to have found more support for the controversial assertion that a toxic microbe called Pfiesteria is responsible for massive fish die-offs along the eastern United States. But the new studies, which include the first rough sketch of the toxin, have failed to convince skeptics.

For 10 years, aquatic ecologist JoAnn Burkholder of North Carolina State University in Raleigh has argued that a potent neurotoxin from the dinoflagellate Pfiesteria has killed more than a billion fish in East Coast estuaries and sickened lab workers and fishers. However, the toxin has not been identified. This past summer, doubts escalated when researchers at the Virginia Institute of Marine Science (VIMS) in Gloucester Point and other universities reported in two top journals that they could not find a toxin, and that Pfiesteria can kill larval fish by feeding on them (Science, 11 October, p. 346).

Toxic or just hungry?

Scientists disagree on how deadly a sugarlike molecule reportedly made by the Pfiesteria microbe (above) is to fish.


Last week, at the 10th International Conference on Harmful Algae in St. Petersburg, Florida, Burkholder said that her critics had not established the right conditions for making Pfiesteria produce toxin. Her lab coaxed the strain of Pfiesteria shumwayae used in the VIMS experiments to kill juvenile tilapia in less than 4 hours, which meets her criteria for toxicity. Collaborating chemist Peter Mueller of the National Oceanic and Atmospheric Administration in Charleston, South Carolina, described a toxic chemical isolated from Burkholder's fish-killing Pfiesteria strains. Burkholder says the NOAA lab also detected this chemical in water and cells from the VIMS strain. It appears to be a glycoside, a molecule that's half sugar, half some other chemical group that hasn't been identified.

Other algal toxin researchers remain skeptical. Wayne Carmichael of Wright State University in Dayton, Ohio, says that, although he knows of one other algal toxin that's a glycoside, this kind is unlikely to cause the neurotoxic effects reported in fish and humans. “It would not explain the range” of observations, he says. VIMS fish pathologist Wolfgang Vogelbein points out that nobody has yet shown that this purified toxin produces the lesions he sees on fish physically attacked by Pfiesteria.

Burkholder's critics want the chance to test her toxic strains. Burkholder, who has long been criticized for not sharing her strains, says that “there were discussions” at the meeting of organizing blind testing of her cultures by other labs, but it's “still in the planning stages.” The key issue, she says, is for other scientists to follow her protocols.

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