Does Pfiesteria Produce Toxins? New Research Suggests Not

Robert E. Gawley - University of Miami
Daniel G. Baden - University of North Carolina at Wilmington
T32ES07320 and P30ES005705

Background: The heterotrophic dinoflagellate Pfiesteria piscicida has received a lot of attention since it was first reported to be responsible for fish kills and human illnesses along the Atlantic coast in 1992. The dinoflagellate was reported to produce one or more toxins in certain strains and at certain periods in a proposed intricate life cycle which is said to contain "amoeba-like" stages. Other researchers in this field have been unable to reproduce these results and thus a major controversy has grown. Defenders of the original hypothesis say that these researchers are using the wrong strain of dinoflagellate. The detractors say that the toxins are produced by another microbe that has contaminated the Pfiesteria cultures and thus, Pfiesteria is not the culprit.

Advance: A team led by researchers at the University of Miami has found that a close relative to P. piscicida, Pfiesteria shumwayae, does not produce the ichthyotoxins postulated to kill fish and harm humans. Simple removal of the dinoflagellate from contaminated water by centrifugation resulted in water that was non-toxic to healthy fish. When the dinoflagellate itself is applied to the fish, sores similar to those reported as evidence of toxin exposure are seen. The researchers speculate that similar infections may make fish more susceptible to other microbes such as a highly pathogenic fungus.

Implication: While not definitively proving that Pfiesteria species are or are not responsible for large fish kills along the east coast, this work suggests that the original hypothesis of the Pfiesteria producing ichthyotoxins responsible for the kills may not be the actual pathogenic mechanism. Additional research soon to be published documenting the chemical structure and potency of a Pfiesteria toxin will provide additional information surrounding this controversy.

Citation: Berry JP, Reece KS, Rein KS, Baden DG, Haas LW, Ribeiro WL, Shields JD, Snyder RV, Vogelbein WK, Gawley RE. Are Pfiesteria species toxicogenic? Evidence against production of ichthyotoxins by Pfiesteria shumwayae. PNAS, U.S.A. Early Addition. 2002 Aug 5.