The Cell From Hell - 1 Billion
Dead Fish To Date
By E.J. Gong Jr. <>
Pfiesteria pisicida Has Multiple Personalities...
Some Of Them Deadly.
For millions of years, Pfiesteria piscicida lived in obscurity on the bottom of rivers and estuaries. No one noticed the microscopic organism and no one cared. All that changed when fish began dying in Maryland and North Carolina. Pfiesteria piscicida can assume 24 different forms, including this fish-killing ameboid stage (North Carolina State University)
Today, the once-obscure single-celled aquatic organism is the topic of congressional hearings, the subject of books and newspaper articles, and the cause of a major decline in the lucrative fishing industries of those two states.
In the past six years, Pfiesteria has killed more than 1 billion fish. But the organism whose name means "fish-killer" in Latin is also dangerous to humans. Scientists and fishermen have developed sores, headaches and other neurological problems from exposure to it.
Scientists are just beginning to understand what makes Pfiesteria so dangerous, and the initial insights are quite fascinating.
Loves Fresh Fish
Pfiesteria is a dinoflagellate, a group of largely saltwater microorganisms, some of whose members are responsible for Red Tide, the phenomenon that makes shellfish dangerous for humans to eat.
Some dinoflagellates behave like plants, getting their energy from photosynthesis. Others, like Pfiesteria, behave like animals, drawing nourishment from fish and microscopic plants and bacteria. In fact, fresh fish appears to be the food of choice when Pfiesteria is in its killer mode. It is the only dinoflagellate that causes massive fish-kills and then disappears within 24 hours. Scientists have found Pfiesteria in rivers and estuaries all along the southeast coast. But the fish-kills have only occurred in Maryland and North Carolina.
The organism has what amounts to multiple personalities, taking on at least 24 different forms as it hunts, feeds, swims and lies dormant. In just a few hours, Pfiesteria can go from rock-hard cyst to fast-swimming hunter to gluttonous amoeba devouring anything in sight.
This shape-shifting ability has made Pfiesteria hard to figure out. JoAnn Burkholder, the foremost expert on the organism, first discovered it about nine years ago while analyzing a fish-kill in North Carolina. Her research team at North Carolina State University in Raleigh has studied it ever since. Their work has provided much of the information and insight into the organism.
From Non-Toxic To Toxic
One of Pfiesteria's harmless forms is as a dormant cyst, minding its own business at the bottom of warm, slow-moving bodies of brackish water (mixtures of fresh and salt). But when the cyst detects the presence of fish nearby, either through the oils or feces they release, it kicks into action.
Pfiesteria transforms itself, leaving its hard shell and swimming up to the fish. Once nearby, it shoots out a powerful toxin that seems to have two effects. First, it makes the fish groggy, so it can't swim away. Then the poison begins to dissolve the fish's skin, creating sores and bleeding.
Then, before dinner time, Pfiesteria undergoes yet another change, this time into an amoebic, jellylike creature that eats flesh and blood. It's a slow, painful death for the fish.
After the meal, the Pfiesteria will revert back to its hard cyst phase and sink back down into the mud. The entire episode all happens in a matter of hours.
Scientists don't understand completely how the Pfiesteria toxins work, but they think there are two distinct types, which Pfiesteria releases in a kind of deadly cocktail. One type is water-soluble and creates the neurological problems for fish.
The second type is fat-soluble, which allows it to penetrate the skin and slowly dissolve the tissue. This second toxin is what produces the characteristic skin ulcerations and sores. Pfiesteria, in its ameboid phase, then slurps up the syrupy mix of flesh and blood.
The Greatest Mystery
Perhaps the greatest mystery of all is what made this ancient cell turn into a mass fish murderer in the past few years. Burkholder and other scientists theorize that environmental changes are to blame. In particular, they say that run-off from nearby farms, especially pig farms in North Carolina, have dumped high levels of animal waste and fertilizer into rivers and lakes. These high levels give rise to blooms of algae and bacteria, which in turn spur a population explosion of Pfiesteria. In cyst form, Pfiesteria feeds on the algae and bacteria.
Burkholder and company will continue to study Pfiesteria, characterizing its potent toxins and determining what exactly causes its population to reach deadly levels. At congressional hearings next week, scientists, federal officials and members of the fishing industry will testify about the threat to humans, and about how to devise better measures to insure public safety.
Scientists are looking for the attention from the media and the government to provide the boost - and the money - needed to fully understand the tiny cell that presents big problems.
When Pfiesteria sits on the river bottom in its non-toxic cyst form, it eats bacteria and algae to survive. But when the tiny creature detects the presence of fish nearby, the cyst turns into a flagellate and swims toward its prey. Once there, it releases a toxin that stuns the fish. Pfiesteria then changes form again, into an amoeba. In this stage, it begins to eat the wounded fish.