NC State Scientists Confirm Second Toxic Pfiesteria Species

Dr. JoAnn M. Burkholder, NC State professor of aquatic botany and marine sciences, says P. shumwayae is the second species identified from "the toxic Pfiesteria complex," a group of closely related dinoflagellate marine organisms believed responsible for killing millions of fish from the Chesapeake Bay to the Gulf of Mexico.

"As our knowledge of these organisms grows and improved techniques become available to detect them, we’ll probably identify a dozen separate species," said Burkholder, the world’s leading Pfiesteria expert. "We’re still just knocking on the door with this discovery."

Burkholder co-discovered the first Pfiesteria species, Pfiesteria piscicida, in 1989. "Piscicida" in Latin means "fish killer."

Research under Burkholder’s direction at the NC State Aquatic Botany Lab found that P. shumwayae -- pronounced "shum-way-eye" -- is genetically and structurally different from its better-known cousin, P. piscicida. Additionally, the two species appear to respond somewhat differently to the enrichment of nutrients that are often overabundant in coastal waters: P. shumwayae appears to thrive best in waters with high levels of nitrogen, while P. piscicida seems to prefer increased phosphorus levels, although both nitrogen and phosphorus can stimulate it to grow.

Scientists first detected P. shumwayae -- which they suspected to be a new species -- during a 1995 fish kill in North Carolina’s New River estuary, following a major spill of effluent from a hog waste lagoon. During two years of testing by Burkholder and associate Howard Glasgow Jr.’s lab, as well as by an independent lab for careful corroboration, all the tests confirmed that the organism is toxic.

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 inhabit the brackish waters of estuaries from the Chesapeake Bay and Pamlico Sound south to the Gulf Coast of Florida and Alabama.

Burkholder named the new species in honor of Dr. Sandra E. Shumway, professor of biology and marine science at Southampton College in New York. "Dr. Shumway is a premier scientist studying harmful algal blooms," she said. "She’s done some of the most significant pioneering research on how toxic algal blooms impact wild and cultured shellfish populations."