Species of the Toxic Pfiesteria Complex, and the Importance of Functional Type in Data Interpretation

Abstract

We describe the two species of the toxic Pfiesteria complex to date (Pfiesteria piscicida and Pfiesteria shumwayae), their complex life cycles, and the characteristics required for inclusion within this complex. These species resemble P. piscicida Steidinger & Burkholder and also have a) strong attraction to fresh fish tissues and excreta, b) toxic activity stimulated by live fish, and c) production of toxin that can cause fish death and disease. Amoeboid stages were verified in 1992-1997 by our laboratory (various stages from toxic cultures) and that of K. Steidinger and co-workers (filose amoebae in nontoxic cultures), and in 2000 by H. Marshall and co-workers (various stages from toxic cultures), from clonal Pfiesteria spp. cultures, using species-specific polymerase chain reaction-based molecular probes with cross-confirmation by an independent specialist. Data were provided from tests of the hypothesis that Pfiesteriastrains differ in response to fresh fish mucus and excreta, algal prey, and inorganic nutrient (N, P) enrichment, depending on functional type or toxicity status. There are three functional types: TOX-A, in actively toxic, fish-killing mode; TOX-B, temporarily nontoxic, without access to live fish for days to weeks, but capable of toxic activity if fish are added; and NON-IND, noninducible with negligible toxicity in the presence of live fish. NON-IND Pfiesteria attained highest zoospore production on algal prey without or without inorganic nitrogen or inorganic phosphorus enrichment. TOX-B Pfiesteria was intermediate and TOX-A was lowest in zoospore production on algal prey with or without nutrients. TOX-A Pfiesteria spp. showed strong behavioral attraction to fresh fish mucus and excreta in short-term trials, with intermediate attraction of TOX-B zoospores and relatively low attraction of NON-IND cultures when normalized for cell density. The data for these clones indicated a potentially common predatory behavioral response, although differing in intensity distinct from a toxicity effect, in attack of fish prey. The data also demonstrated that functional types of Pfiesteria spp. show distinct differences in response to fish, algal prey, and inorganic nutrient enrichment. Collectively, the experiments indicate that NON-IND strains should not be used in research to gain insights about environmental controls on toxic strains of Pfiesteria spp.

Demonstration of toxicity to fish and to mammalian cells by Pfiesteria species: Comparison of assay methods and strains

“…Additional PfTx is being produced (chemical structure being published elsewhere) so that standards can be developed for routine use. In the interim, various fish assays have been used in attempts to detect toxic Pfiesteria strains (5,6,(10)(11)(12)(21)(22)(23)(24)(25). Although some techniques have provided evidence of toxicity to fish (5,10,14,24), researchers using other methods have concluded that Pfiesteria is not toxigenic at the species [P. shumwayae (21,22)] or genus (23,25) levels.…”

“…Under conditions conducive to toxicity expression (9)(10)(11), actively toxic (TOX-A) strains, grown with live finfish, are capable of killing fish with toxin involvement at low to moderate cell densities (Ն4 ϫ 10 2 to 10 3 cells per ml, minutes to several hours). Impacts are exacerbated by Pfiesteria physical attack (6,7,12). The same strains separated from live fish for days or longer can sometimes produce sufficient exotoxin to cause death of sensitive larval stages without physical contact (7).…”

“…The same strains separated from live fish for days or longer can sometimes produce sufficient exotoxin to cause death of sensitive larval stages without physical contact (7). Noninducible (NON-IND) strains apparently are incapable of killing fish with toxin (1,6,8).…”

“…Previous research has established that toxicity is highly variable among strains within a given toxic algal species (4), including Pfiesteria spp., ranging from strains with negligible toxicity to highly toxic strains (1,(5)(6)(7). Pfiesteria strains can cause larval fish death by physical attack (1).…”

Emerging areas of research reported during the CDC National Conference on Pfiesteria: from biology to public health.

“…In preparation for the conference an expert peer-review panel was commissioned to review the existing literature and identify research gaps; the summary of their review is published in this monograph (17). During the meeting, primary Pfiesteria researchers presented previously unpublished results; the majority of those presentations are presented as peer-reviewed articles in this monograph (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). The discussion portion of the conference focused upon researcheridentified research gaps.…”