Spotlight on Research: Findings Cast Doubt on Pfiesteria Theory

Posted: February 17, 2005 at 1:00 am, Last Updated: November 30, -0001 at 12:00 am

By Patty Snellings

For more than a decade, Pfiesteria—a single-celled dinoflagellate—has been targeted by scientists at North Carolina State University (NCSU) and their colleagues at other research institutions as the cause of massive fish kills in estuaries off the coasts of North Carolina, Virginia, and Maryland. Widely published research asserts that two species of Pfiesteria pass through a complex multistage life cycle. As they transform from a dinozoite to an amoeboid stage, it is believed they excrete a toxin that kills fish and poses a public health threat.

But research findings from George Mason scientists challenge these claims.

In collaboration with the Center of Marine Biotechnology at the University of Maryland Biotechnology Institute, George Mason’s Patrick Gillevet, a scientist in the Department of Environmental Science and Policy, and affiliate professor Thomas Nerad began their Pfiesteria studies in 1999 with funding from the Environmental Protection Agency.

Their initial studies examined the proposed multistage life cycle of the organism and found no evidence of a transformation process. “The controversy over the life cycle of Pfiesteria most likely would not have occurred if the individuals describing these dinoflagellates had collaborated with an expert in amoeba taxonomy,” explains Nerad. “Our findings challenge the reports that Pfiesteria has an unusual dinoflagellate life cycle that includes an amoeboid stage.”

Patrick Gillevet
Patrick Gillevet
Photo by Evan Cantwell

These results were presented in December 2003 at the Second Symposium on Harmful Marine Algae in the United States, and the study was later published in the Journal of Eukaryotic Microbiology (September-October 2004).

A second study, published in Applied and Environmental Microbiology (January 2005), failed to validate the existence of a toxin. “No toxins were isolated from Pfiesteria,” Gillevet confirms. “There is no direct correlation between Pfiesteria and fish death.”

Gillevet says the popular theory about Pfiesteria is based on reports that were never properly confirmed. “Experiments to investigate the Pfiesteria toxicity were set up in fish tanks full of other contaminating organisms,” he explains. “Clearly, it was not rigorous science.”

Three techniques should have been used in the NCSU studies to investigate Pfiesteria’s life cycle, according to Nerad: transmission electron microscopy rather than scanning electron microscopy; videotape documentation; and DNA sequencing of the small subunit ribosomal RNA gene of both the dinozoite and amoeboid stages. “Why these techniques were not utilized is puzzling and inexplicable.”

Gillevet and Nerad agree that the scientific literature needs to be revised, and future editions of biology textbooks should be modified to reflect the current state of knowledge about Pfiesteria. “Scientists have an obligation to clarify the literature when what they publish is incorrect. Otherwise, a disservice is done to all of science,” Nerad says.

“Complex science is difficult,” says Gillevet. “You have to be an advocate for your own research, but you have to be self-critical, too.”

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