More controversy surrounds Pfiesteria
Thursday, 20 June 2002
The highly controversial multi-staged Pfiesteria microbe that has been blamed for large fish kills on America’s Atlantic seaboard might be innocent if new research mapping its life cycle is correct.
The research undertaken by molecular biologists at the University of North Carolina School of Medicine used molecular probes to observe Pfiesteria piscicida in tanks for two years. They did not observe the dinoflagellate microbe forming some of the previously reported toxic life-stages.
"Our study found no evidence to support the presence of the amoeba stages, many of which were originally reported to be toxic," said Dr Wayne Litaker, the principal author of the study.
The work will be published in this month's issue of Journal of Phycology.
Large fish kills during the 1980's and 1990's in the estuaries and waterways of Chesapeake Bay and North Carolina were attributed to some of the life stages of Pfiesteria piscicida by Dr JoAnn Burkholder, from the Center for Applied Aquatic Ecology at North Carolina State University.
Dr Burkholder's research, identifying 24 life cycle stages (including several that were toxic) was published in 1992, 1993 and 1997. Considerable controversy has surrounded this finding. The presence of the toxic form of Pfiesteria piscicida was attributed to nutrients running into the water from chicken and pig farms in the nearby area - causing an outcry from the swine industry.
The new research which maintained fish tanks under conditions similar to those described by the previous researcher found that the life cycle of Pfiesteria piscicida was not dissimilar to other marine dinoflagellates as previously reported.
The work was undertaken using a cloned culture of Pfiesteria piscicida. One of the clones originated from a tank inoculated with water from North Carolina's Pamlico River in 1991 that had been killing fish since that time.
To study Pfiesteria’s life cycle the researchers used nuclear stains, light microscopy, high resolution video microscopy and electron microscopy. They also used in situ hybridisation with a suite of fluorescently-labelled peptide nucleic acid (PNA) probes - one of the first times PNA technology has been used in phytoplankton research.
The study did find not amoebae in the tanks until fish were introduced, and the researchers attribute them to contaminant microorganisms harboured by all fish.
They maintain that this contamination means that it is not possible to determine life cycle stages of Pfiesteria piscicida without using molecular probes specific to particular species. The PNA probes had not yet been developed when the original life-cycle study was undertaken.
"Consequentially, any ecological role or potential toxicity ascribed to specious Pfiesteria piscicida based on the original fish tank studies should be re-examined," they write.
There are several species of Pfiesteria, including one found in Australian waters which is being monitored.