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|NOAA News Releases 2002
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The singled-celled organism, Pfiesteria piscicida, associated with fish kills and human health problems in the mid-1990s in North Carolina and Maryland has a very simple life cycle, say scientists from the Commerce Department's National Oceanic and Atmospheric Administration. This conclusion is based on results of a new federally funded and peer-reviewed study published in the June 20 issue of the Journal of Phycology, the leading US publication on marine and freshwater algae.
Researchers from NOAA, the University of North Carolina and North Carolina State University used highly sophisticated molecular technology adapted from medical research for closer study of Pfiesteria. With the help of this new technology, NOAA researchers were able to show that Pfiesteria has a simple life cycle like many similar marine dinoflagellates. Past research has shown Pfiesteria to have a complex 24-stage life cycle that included many toxic amoeboid stages. The new research revealed no amoeboid stages in Pfiesteria's life cycle, bringing into question the nature of the toxicity ascribed to this species.
"Our carefully controlled studies, including those where Pfiesteria had been reared under conditions reported to produce amoebae, found no evidence of an exotic life cycle involving multiple amoeboid stages," said study co-author Dr. Patricia A. Tester, of NOAA's Center for Coastal Fisheries and Habitat Research, in Beaufort, N.C. "Rather, the life cycle of Pfiesteria is similar to the life cycles of other marine dinoflagellates."
"Even though we found that Pfiesteria does not have toxic amoeboid stages, that does not mean Pfiesteria or other toxic harmful algal bloom species should not be of concern to the health of America's estuaries and coastal regions," said study co-author Dr. R. Wayne Litaker, of NOAA's Center for Coastal Fisheries and Habitat Research and University of North Carolina's Program in Molecular Biology and Biotechnology. "Our work is far from done if we are to better understand the causes of fish kills and associated human health concerns. Ongoing research will therefore seek to zero-in on the potential causes of these problems. This research is a giant step forward in understanding how Pfiesteria works, and we now know our focus must extend well beyond Pfiesteria alone."
The primary tool used in this study was a "fluorescently labeled peptide nucleic acid (PNA) probe" recently developed for use in medical research. The use of PNA probes in this study represents one of the first times this technology has been used in marine research. The probe used in this study was designed to bind specifically to a unique DNA sequence only found in Pfiesteria piscicida. To find that unique Pfiesteria DNA sequence, the researchers sequenced a region of DNA from more than 100 cell isolates of Pfiesteria and closely related species. These sequences were aligned using sophisticated computer technologies so that a sequences only found in Pfiesteria could be identified. A PNA probe that would only bind the unique Pfiesteria sequence was then synthesized. The PNA was next mixed with Pfiesteria cells taken from cultures where Pfiesteria was exposed to either fish or other algae cells. The Pfiesteria-specific PNA entered the cells in each sample, but only bound to the Pfiesteria life cycle stages carrying the unique DNA sequence.
The results of the PNA probe studies also were confirmed by carefully observing the life cycle using high-resolution microscopy. Other tests, including amoeba-specific PNA probes, showed that any amoebae in the Pfiesteria tanks were different species commonly found in estuaries and not part of the Pfiesteria life cycle. These "normal" amoebae species were contaminants introduced by the fish and were present in the fish tank even before Pfiesteria cells were added. The study underscores the need for further research to determine causes of fish kills and public health problems previously reported to be associated solely with Pfiesteria exposures.
"This public investment in Pfiesteria research is paying off. PNA technology has opened a door to better understanding of toxic phytoplankton and their risks to coastal resources and public health," said Tester. "The new scientific opportunities could help in detecting toxic algal species and could improve monitoring and early warning systems designed to protect those resources."
Joining Tester as co-authors of the research report are principal author Dr. R. Wayne Litaker, NOAA's Center for Coastal Fisheries and Habitat Research and University of North Carolina's Program in Molecular Biology and Biotechnology, Mark W. Vandersea and Steven R. Kibler, NOAA Center for Coastal Fisheries Habitat Research program; Dr.Victoria J. Madden of the University of North Carolina's Microscopy Services Laboratory, Pathology and Laboratory Medicine; and Dr. Edward J. Noga, Department Of Clinical Sciences, North Carolina State University College of Veterinary Medicine.
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