Researchers have discovered other Pfiesteria "lookalike" organisms, but P. shumwayae is the first truly Pfiesteria-like organism - besides P. piscicida - to be found harmful to fish.
Burkholder said that the life cycle and behavior of P. shumwayae are identical to those of P. piscicida. Like P. piscicida, the newly described species has a complex series of life stages, most of which are nontoxic. "So far, we've confirmed that 19 of its stages are similar to those of piscicida, and we believe that it's only a matter of time before we verify that the other stages are also the same," she said.
Most of those stages are nontoxic in both species. In the presence of live fish, however, several stages of both species generate toxins that stun the fish and cause open sores on their skin; the microbes then feed on the fish tissue and blood. Both also prefer to prey on the same kinds of algae when fish are not available, and can "steal" plant-like organelles from algae to masquerade as microscopic plants.
NC State researchers, however, found dissimilarities in the structure and the genetic makeup of the two species. Molecular probes identified a 3 percent difference between the two species' DNA. Glasgow spent 200 hours over two years mapping the surface of hundreds of Pfiesteria zoospores using a scanning electron microscope. In so doing, he found that many specimens had a different "fingerprint" - they had a four-sided structural plate on the outside of the cells where P. piscicida had a three-sided plate.
"The difference between these species is the difference between a diamond and a triangle," Burkholder explained.
Thus far, P. shumwayae has been found to overlap the geographic distribution of P. piscicida: The single-celled organisms inhab
Contact: Kevin Potter
North Carolina State University