Dinoflagellate Pfiesteria Research Articles

The Eukaryotic Life on Microplastics in Brackish Ecosystems

Microplastics (MP) constitute a widespread contaminant all over the globe. Rivers and wastewater treatment plants (WWTP) transport annually several million tons of MP into freshwaters, estuaries and oceans, where they provide increasing artificial surfaces for microbial colonization. As knowledge on MP-attached communities is insufficient for brackish ecosystems, we conducted exposure experiments in the coastal Baltic Sea, an in-flowing river and a WWTP within the drainage basin. While reporting on prokaryotic and fungal communities from the same set-up previously, we focus here on the entire eukaryotic communities. Using high-throughput 18S rRNA gene sequencing, we analyzed the eukaryotes colonizing on two types of MP, polyethylene and polystyrene, and compared them to the ones in the surrounding water and on a natural surface (wood). More than 500 different taxa across almost all kingdoms of the eukaryotic tree of life were identified on MP, dominated by Alveolata, Metazoa, and Chloroplastida. The eukaryotic community composition on MP was significantly distinct from wood and the surrounding water, with overall lower diversity and the potentially harmful dinoflagellate Pfiesteria being enriched on MP. Co-occurrence networks, which include prokaryotic and eukaryotic taxa, hint at possibilities for dynamic microbial interactions on MP. This first report on total eukaryotic communities on MP in brackish environments highlights the complexity of MP-associated biofilms, potentially leading to altered microbial activities and hence changes in ecosystem functions.

Still Acting Green: Continued Expression of Photosynthetic Genes in the Heterotrophic Dinoflagellate Pfiesteria piscicida (Peridiniales, Alveolata)

The loss of photosynthetic function should lead to the cessation of expression and finally loss of photosynthetic genes in the new heterotroph. Dinoflagellates are known to have lost their photosynthetic ability several times. Dinoflagellates have also acquired photosynthesis from other organisms, either on a long-term basis or as “kleptoplastids” multiple times. The fate of photosynthetic gene expression in heterotrophs can be informative into evolution of gene expression patterns after functional loss, and the dinoflagellates ability to acquire new photosynthetic function through additional endosymbiosis. To explore this we analyzed a large-scale EST database consisting of 151,091 unique sequences (29,170 contigs, 120,921 singletons) obtained from 454 pyrosequencing of the heterotrophic dinoflagellate Pfiesteria piscicida. About 597 contigs from P. piscicida showed significant homology (E-value <e−30) with proteins associated with plastid and photosynthetic function. Most of the genes involved in the Calvin-Benson cycle were found, genes of the light-dependent reaction were also identified. Also genes of associated pathways including the chorismate pathway and genes involved in starch metabolism were discovered. BLAST searches and phylogenetic analysis suggest that these plastid-associated genes originated from several different photosynthetic ancestors. The Calvin-Benson cycle genes are mostly associated with genes derived from the secondary plastids of peridinin-containing dinoflagellates, while the light-harvesting genes are derived from diatoms, or diatoms that are tertiary plastids in other dinoflagellates. The continued expression of many genes involved in photosynthetic pathways indicates that the loss of transcriptional regulation may occur well after plastid loss and could explain the organism's ability to “capture” new plastids (i.e. different secondary endosymbiosis or tertiary symbioses) to renew photosynthetic function.

Axenic Culture of the Heterotrophic Dinoflagellate Pfiesteria shumwayae in a Semi‐Defined Medium

A semi-defined, biphasic culture medium was developed that supported the axenic growth of three strains of the heterotrophic dinoflagellate Pfiesteria shumwayae. Maximum cell yields and division rates in the semi-defined medium ranged from 0.1 x 10(5) to 4.0 x 10(5) cells/ml and 0.5 to 1.7 divisions/day, respectively, and depended on the concentration of the major components in the medium as well as the P. shumwayae strain. The medium contained high concentrations of certain dissolved and particulate organic compounds, including amino acids and lipids. Pfiesteria shumwayae flagellated cells were attracted to insoluble lipids present in the medium and appeared to feed on the lipid particles, suggesting that phagocytosis may be required for growth in axenic culture. Development of a semi-defined medium represents significant progress toward a completely defined axenic culture medium and subsequent determination of the biochemical requirements of P. shumwayae, needed to advance understanding of the nutritional ecology of this species. Further, this medium provides an economical, simplified method for generating high cell densities of P. shumwayae in axenic culture that will facilitate controlled investigations on the physiology and biochemistry of this heterotrophic dinoflagellate.

Detection of Heterotrophic Dinoflagellate Pfiesteria piscicida (Dinophyceae) in Surface Water Samples Using Real-time PCR

Heterotrophic dinoflagellate Pfiesteria piscicida (Dinophyceae) has been claimed to produce potent ichthyotoxins that cause disorientation and eventually death of fish and other marine animals. A real-time PCR probe targeting for SSU rRNA gene was used for detection of P. piscicida in Chinhae Bay, Korea. PCR inhibitors were successfully removed by dilution of template DNA. Positive detections were shown from surface water samples indicating the presence of P. piscicida in Chinhae Bay.

Use of molecular markers for early warning detection of harmful algal blooms

Harmful Algal Blooms (HABs) are a biological hazard for, and can also result from, aquaculture. To minimise economic and environmental impacts, an early warning detection system is needed. In this paper, two most commonly used molecular techniques are introduced with applications and examples involving work on the putatively toxic dinoflagellate Pfiesteria piscicida. Unlike previous reviews giving comprehensive accounts of the detection of HABs, this paper focuses on the technical aspects of the methods in an attempt to provide information potentially helpful for those who have little or no prior experience in molecular techniques but wish to apply these techniques to species of their interest.

Detection of a novel ecotype of Pfiesteria piscicida (Dinophyceae) in an Antarctic saline lake by real-time PCR

The heterotrophic dinoflagellate Pfiesteria piscicida was detected in Ace Lake in the Vestfold Hills, eastern Antarctica by using real-time PCR based on 18S rDNA sequences. Antarctic water samples collected in 2004 were tested by species-specific real-time PCR assays for the identification of P. piscicida and P. shumwayae. Positive results were shown with P. piscicida-specific real-time PCR, and PCR products were examined by sequence analysis for confirmation. A phylogenetic tree made from partial 18S rDNA sequences showed that the Antarctic clone clustered with P. piscicida. This result suggests that P. piscicida is present in the extreme conditions of an Antarctic saline lake which has not contained fish for thousands of years.

Distribution of the heterotrophic dinoflagellate Pfiesteria piscicida in Korean waters and its consumption of mixotrophic dinoflagellates, raphidophytes and fish blood cells

To explore the distribution of Pfiesteria piscicida in Korean coastal waters, we analyzed the morphology and DNA sequence of several isolates collected from 6 locations along the southern and western Korean coasts. We also investigated the prey species consumed by a Korean isolate and determined the growth and ingestion rates of P. piscicida when it fed on the dinoflagellate Amphidinium carterae, an unidentified cryptophyte species, and the raphidophyte Heterosigma akashiwo. Additionally, these parameters were measured when the isolate was fed perch blood cells and the cryptophyte Rhodomonas salina. Furthermore, we calculated grazing coefficients by combining field data on abundance of P. piscicida (and Pfiesteria-like dinoflagellates) with laboratory data on ingestion rates. The DNA sequence of a P. piscicida isolate from Masan Bay was identical to USA isolates, whereas DNA sequences of isolates from Busan, Incheon, Kunsan, Kwangyang, and Yeosu differed by 1 bp from USA isolates. Among the prey offered, P. piscicida was able to feed on all naked mixotrophic dinoflagellates, the smallest thecate mixotrophic dinoflagellates Heterocapsa rotundata, and all raphidophytes, but not on large thecate dinoflagellates. Perch blood cells were the optimal prey. Maximum growth rates of P. piscicida fed on perch blood cells, R. salina, A. carterae, the cryptophyte, and H. akashiwo were 1.74, 1.41, 1.22, 1.15, and 1.10 d -1 , respectively. The maximum ingestion rate of P. piscicida when fed perch blood cells (4.3 ng C predator -1 d -1 ) was much higher than those when fed R. salina, H. akashiwo, A. carterae, or the cryptophyte (0.4 to 1.7 ng C predator -1 d -1 ). Calculated grazing coefficients on co-occurring Amphidinium spp., H. akashiwo, and cryptophytes were up to 1.07, 0.45, and 0.22 h -1 , respectively. Our results suggest that grazing by P. piscicida potentially has a considerable effect on algal populations.

Motility is involved in Silicibacter sp. TM1040 interaction with dinoflagellates

Silicibacter sp. TM1040, originally isolated from a culture of the dinoflagellate Pfiesteria piscicida, senses and responds to the dinoflagellate secondary metabolite dimethylsulfoniopropionate (DMSP) by flagella-mediated chemotaxis behaviour. In this report we show that swimming motility is important for initiating the interaction between the bacterium and dinoflagellate. Following transposon mutagenesis, three mutants defective in wild-type swimming motility (Mot-) were identified. The defects in motility were found to be in homologues of cckA and ctrA, encoding a two-component regulatory circuit, and in a novel gene, flaA, likely to function in flagellar export or biogenesis. Mutation of flaA or cckA results in the loss of flagella and non-motile cells (Fla-), while CtrA- cells possess flagella, but have reduced motility due to increased cell length. All three Mot- mutants were defective in attaching to the dinoflagellate, particularly to regions that colocalized with intracellular organelles. The growth rate of the dinoflagellates was reduced in the presence of the Fla- mutants compared with Fla+ cells. These results indicate that bacterial motility is important for the Silicibacter sp. TM1040-P. piscicida interaction.

Remember Pfiesteria ?: Occupational Exposure Unlikely to Cause Cognitive Effects

Vol. 114, No. 7 EnvironewsOpen AccessRemember Pfiesteria?: Occupational Exposure Unlikely to Cause Cognitive Effectsis accompanied byOccupational Exposure to Pfiesteria Species in Estuarine Waters Is Not a Risk Factor for Illness Tanya Tillett Tanya Tillett Search for more papers by this author Published:1 July 2006https://doi.org/10.1289/ehp.114-a429bAboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Case reports have suggested that exposure to the dinoflagellate Pfiesteria may contribute to deficits in human learning and memory. Until now, however, there has been no clear, objective documentation of health effects associated with regular occupational exposure to this organism. The results of the first systematic, multiyear study of Pfiesteria’s human health effects now demonstrate that commercial fishermen (“watermen”) likely do not face significant health risks from routine occupational exposure to the organism [EHP 114:1038–1043; Morris et al.].Pfiesteria is a common inhabitant of estuarine waters in the U.S. mid-Atlantic region in the summer and fall. In 1997, watermen working along the Pocomoke River, an estuary off Chesapeake Bay, experienced a pattern of neuropsychological deficits in association with fish kills linked to Pfiesteria outbreaks. Researchers studying Pfiesteria in a lab environment had reported similar memory and learning deficits.Using a cohort of 88 healthy watermen with regular occupational exposure to Chesapeake Bay waters and 19 controls with minimal contact to the waters (matched to the watermen by zip code, age, and educational level), a team of Maryland researchers collected data over four summers, from 1999 through 2002. They questioned the subjects biweekly about symptoms like those reported in the 1997 episode and about their exposure to the waters and to known chemical toxicants. Subjects were tested at the beginning and end of each summer season on sensory and motor functions, attention and concentration, memory, visual functions, and verbal functions. In addition, the research team analyzed more than 3,500 water samples taken from Chesapeake Bay to monitor the presence of Pfiesteria and other harmful species.P. piscicida was found in water samples drawn from a number of locations in all four years of the study, and P. shumwayae (recently renamed Pseudopfiesteria shumwayae) was found in the last two years. However, the investigators found no decline in neurological function among the watermen in any year of the study.The scientists note that unique, isolated instances of Pfiesteria outbreaks or unusually toxic strains of the dinoflagellate may have been associated with the marked, reversible health effects documented in the past. They point out that the present study is congruent with similar studies in North Carolina and Virginia in providing reassurance that in the absence of these conditions, watermen do not appear to face significant health risks from routine occupational exposure to estuarine waters that contain Pfiesteria.Safe from PfiesteriaNew data suggest commercial fishermen need not fear routine exposure to the organism.FiguresReferencesRelatedDetailsRelated articlesOccupational Exposure to Pfiesteria Species in Estuarine Waters Is Not a Risk Factor for Illness18 April 2006Environmental Health Perspectives Vol. 114, No. 7 July 2006Metrics About Article Metrics Publication History Originally published1 July 2006Published in print1 July 2006 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Effects of the estuarine dinoflagellate Pfiesteria shumwayae (Dinophyceae) on survival and grazing activity of several shellfish species

A series of experiments was conducted to examine effects of four strains of the estuarine dinoflagellate, Pfiesteria shumwayae, on the behavior and survival of larval and adult shellfish (bay scallop, Argopecten irradians; eastern oyster, Crassostrea virginica; northern quahogs, Mercenaria mercenaria; green mussels, Perna viridis [adults only]). In separate trials with larvae of A. irradians, C. virginica, and M. mercenaria, an aggressive predatory response of three strains of algal- and fish-fed P. shumwayae was observed (exception, algal-fed strain 1024C). Larval mortality resulted primarily from damage inflicted by physical attack of the flagellated cells, and secondarily from Pfiesteria toxin, as demonstrated in larval C. virginica exposed to P. shumwayae with versus without direct physical contact. Survival of adult shellfish and grazing activity depended upon the species and the cell density, strain, and nutritional history of P. shumwayae. No mortality of the four shellfish species was noted after 24 h of exposure to algal- or fish-fed P. shumwayae (strains 1024C, 1048C, and CCMP2089) in separate trials at ≤5 × 10 3 cells ml −1, whereas higher densities of fish-fed, but not algal-fed, populations (>7–8 × 10 3 cells ml −1) induced low (≤15%) but significant mortality. Adults of all four shellfish species sustained >90% mortality when exposed to fish-fed strain 270A1 (8 × 10 3 cells ml −1). In contrast, adult M. mercenaria and P. viridis exposed to a similar density of fish-fed strain 2172C sustained <15% mortality, and there was no mortality of A. irradians and C. virginica exposed to that strain. In mouse bioassays with tissue homogenates (adductor muscle, mantle, and whole animals) of A. irradians and M. mercenaria that had been exposed to P. shumwayae (three strains, separate trials), mice experienced several minutes of disorientation followed by recovery. Mice injected with tissue extracts from control animals fed cryptomonads showed no response. Grazing rates of adult shellfish on P. shumwayae (mean cell length ±1 standard error [S.E.], 9 ± 1 μm) generally were significantly lower when fed fish-fed (toxic) populations than when fed populations that previously had been maintained on algal prey, and grazing rates were highest with the nontoxic cryptomonad, Storeatula major (cell length 7 ± 1 μm). Abundant cysts of P. shumwayae were found in fecal strands of all shellfish species tested, and ≤45% of the feces produced viable flagellated cells when placed into favorable culture conditions. These findings were supported by a field study wherein fecal strands collected from field-collected adult shellfish ( C. virginica, M. mercenaria, and ribbed mussels, Geukensia demissa) were confirmed to contain cysts of P. shumwayae, and these cysts produced fish-killing flagellated populations in standardized fish bioassays. Thus, predatory feeding by flagellated cells of P. shumwayae can adversely affect survival of larval bivalve molluscs, and grazing can be depressed when adult shellfish are fed P. shumwayae. The data suggest that P. shumwayae could affect recruitment of larval shellfish in estuaries and aquaculture facilities; shellfish can be adversely affected via reduced filtration rates; and adult shellfish may be vectors of toxic P. shumwayae when shellfish are transported from one geographic location to another.

Effect of small-scale shear on grazing and growth of the dinoflagellate Pfiesteria piscicida

Low turbulence environments have been hypothesized to be necessary for toxic outbreaks of the heterotrophic/mixotrophic dinoflagellate Pfiesteria piscicida. A toxic Pfiesteria outbreak occurred in the shallow waters (the flats) of the lower Pocomoke River, MD, USA, in 1997. During August 1999 and May and August 2000, data were collected with a Shallow Water ADV Turbulence Tripod (SWATT) to estimate turbulent shear at a location monitored for Pfiesteria on the flats. Approximately 78% of the observed shears were ≤1 s −1 and 98% were ≤2 s −1. Densities of Pfiesteria-like dinoflagellates were low in the Pocomoke River during 1999 and 2000 and no toxic outbreaks occurred. In the laboratory, Couette cylinders were used to determine the effect of small-scale shear on feeding and growth of cultured P. piscicida growing on cryptophyte prey. Shear of 1 s −1 had little or no effect on feeding or growth but 3 s −1 reduced feeding and survival/growth of Pfiesteria zoospores. Small, rapidly dividing Pfiesteria cells were most susceptible to negative effects of shear. Pfiesteria appears to be more sensitive to small-scale shear than are most autotrophic dinoflagellates. However, in the lower Pocomoke River, turbulent shear is rarely high enough to inhibit the growth of non-toxic Pfiesteria zoospores. Toxic functional types (TOX-A and TOX-B) may be more sensitive to small-scale shear; it will be important to determine the responses of these types of Pfiesteria in order to predict the affects of wind and tidal mixing on toxic outbreaks.

Cholestyramine Improves Tropical-Related Diarrhea

Patients exposed to the toxic dinoflagellate Pfiesteria develop an illness characterized by secretory diarrhea, conjunctival irritation, skin lesions, and varying degrees of neurologic manifestations. The anion-exchange resin, cholestyramine has been reported in one small case series to be an effective treatment of severe diarrhea associated with Pfiesteria intoxication. A 54-year-old man traveled to the Dominican Republic where he went swimming in what he describes as "dirty ocean water". Within an hour, he noted a generalized burning and itching of his skin. Later on, he noted pruritic vesicular skin lesions, intense frontal headache, and conjunctivitis. A few days later, he complained of abdominal cramping, nausea, and hourly episodes of watery, non-bloody diarrhea. Due to the constellation of symptoms, Pfiesteria intoxication was suspected. On arrival in the United States, he sought medical care for continued symptoms. Physical examination was remarkable for conjunctival injection, linear vesicular lesions (5 cm in length) over his right ankle and left orbit as well as erythema over foreskin of his penis. Mental status and memory were normal. Laboratory studies revealed an elevated serum creatinine, which eventually normalized, and stool studies were negative for leukocytes, blood, and enteric pathogens. Intense diarrhea persisted until he was started on cholestyramine (4 g PO tid). The diarrhea resolved within 2 hours of starting treatment. The headache was initially treated with narcotic agents but only resolved with IV diphenhydramine (25 mg q 4 h). Cholestyramine and diphenhydramine appear to be effective therapeutic agents for tropical-related diarrhea and headache, respectively.

Occupational Exposure to Pfiesteria Species in Estuarine Waters Is Not a Risk Factor for Illness

BackgroundExposure to the dinoflagellate Pfiesteria has, under certain circumstances, been associated with deficits in human learning and memory. However, uncertainties remain about the health risk of chronic, low-level exposures (as seen among occupationally exposed commercial fishermen), particularly in light of studies suggesting that Pfiesteria strains are widespread in the estuarine environment in the U.S. mid-Atlantic region.MethodsWe selected an initial cohort of 152 persons, including 123 persons with regular, occupational exposure to the Chesapeake Bay; 107 of the cohort members were followed for the full four summer “seasons” of the study. Cohort members were questioned biweekly about symptoms, and data were collected about the areas of the bay in which they worked. These latter data were matched with data on the presence or absence of Pfiesteria in each area, based on polymerase chain reaction analysis of > 3,500 water samples. Cohort members underwent neuropsychological testing at the beginning and end of each summer season.ResultsNo correlation was found between work in an area where Pfiesteria was identified and specific symptomatology or changes on neuropsychological tests.ConclusionsAlthough high-level or outbreak-associated exposure to Pfiesteria species (or specific strains within a species) may have an effect on health, routine occupational exposure to estuarine environments in which these organisms are present does not appear to pose a significant health risk.

Contaminant-free cultivation of Pfiesteria shumwayae (Dinophyceae) on a fish cell line

Geographically distinct strains of the heterotrophic dinoflagellate Pfiesteria shumwayae were cultivated on a fish cell line in the apparent absence of bacteria and other microbial conta- minants. Cultures were established with a high rate of success by inoculating single purified P. shumwayae cells into fish cell cultures containing a simple saltwater medium suitable for both cell types, and resulting isolates were serially cultivated on fish cells for months without visible signs of abnormality or reduced viability. P. shumwayae fed phagocytically on the fish cells and exhibited higher cell production than reported using other culturing methods. Compared to previous methods of studying the interaction between Pfiesteria spp. and fishes, this system enabled closer and more direct observation of the dinoflagellates and was also more economical and sustainable as a culturing method. The absence of bacteria and other contaminating microorganisms should facilitate important physiological and biochemical investigations. The methods used were inadequate for cultivating strains of P. piscicida, suggesting a possible difference in nutritional requirements between the 2 Pfiesteria species.

Predator–prey interactions between a planktonic ciliate Strombidium sp. (Ciliophora, Oligotrichida) and the dinoflagellate Pfiesteria piscicida (Dinamoebiales, Pyrrophyta)

The functional response of a planktonic ciliate, Strombidium sp. feeding on the dinoflagellate Pfiesteria piscicida non-toxic zoospores (NTZ) was experimentally studied with four different prey concentrations (43–3153 cells ml −1). Data from direct observations (NTZ inside individual Strombidium sp.) was used to calculate predator–prey specific ingestion and clearance rates. The ingestion rates varied between 0.68 and 14.26 NTZ ind −1 h −1, and with the predator–prey specific handling time of 2.83 min the U max was 21.18 NTZ ind −1 h −1. The increase in the prey concentration between approximately 700 and 3000 NTZ ml −1 did not increase the uptake of prey, and at the lowest Pfiesteria NTZ concentrations the feeding efficiency of Strombidium sp. was lowered, possibly indicating a situation of threshold feeding. When data from direct observations of ingested Pfiesteria NTZ were compared with values of total NTZ loss from the experimental water during the experiment, ingestion was found to represent only a fraction of the total NTZ loss in the presence of ciliates. This discrepancy was concluded to be due to other grazer related factors than actual ciliate grazing. The control of the initial growth of Pfiesteria community, in a pre-bloom situation, would require only a small ciliate abundance (less than 5 ml −1), but when the Pfiesteria NTZ are scarce, relatively more ciliates are needed to limit the population growth of the dinoflagellate community because of the apparent feeding threshold. It is concluded that the formation of non-toxic P. piscicida blooms require periods of low grazing pressure or a means to escape grazing.

Development of an immunofluorescence technique for detecting Pfiesteria piscicida

While several DNA-based methods have been developed for the putatively toxic dinoflagellate Pfiesteria piscicida Burkholder et Steidinger, an independent detection method such as immunofluorescence can be a useful alternative. In this study, P. piscicida-specific antisera were developed, and an immunofluorescence (IF) procedure was optimized. A total of six antisera were raised using whole cells (WCA) and the insoluble cellular fraction (ICF) as antigens, respectively, and their titer and specificity were examined using dot blot analysis and whole cell IF. Results showed that the two antisera produced from the ICF antigen had a markedly higher titer (1500) than the other four yielded from the WCA (200). In addition, the two ICF-derived antisera exhibited much higher species specificity, showing no cross-reaction with P. shumwayae, Cryptoperidiniopsis sp., Karlodinium micrum, and other more distant algae tested, and very low background for field collected samples. In evaluation of the IF technique using a P. piscicida-specific polymerase chain reaction (PCR) technique, results from both methods generally agreed well for both field samples (from eastern Long Island Sound) spiked with cultured P. piscicida and those containing naturally occurring P. piscicida (from Chesapeake Bay tributaries).

Enhancing Causal Assessment of Estuarine Fishkills Using Graphical Models

It is not possible to determine the causal relationship between fishkills and the toxic dinoflagellate Pfiesteria piscicida in the Neuse River Estuary, North Carolina, using observational data on these two variables alone. However, consideration of a third variable, indicating the presence of a broader class of more easily measured Pfiesteria-like organisms (PLOs), leads to causal model structures from which the nature of this relationship can be distinguished. We use reported field data to evaluate alternative models and find that the suggestion that toxic Pfiesteria cause fishkills is inconsistent with observation. The data are more indicative of a model in which PLOs (including potentially toxic Pfiesteria) are stimulated to become actively toxic by the presence of already dead or dying fish. Laboratory experiments performed to date do not provide evidence contradictory to this finding. However, neither can the existence of a common cause of both Pfiesteria toxicity and fishkills be ruled out. The differing implications for ecosystem management suggest that these causal associations should be further investigated through additional modeling and data collection efforts. Graphical methods of model construction and evaluation can assist in this process.

Is Sugary Toxin the Smoking Gun?

PFIESTERIA DEBATE A team of researchers claims to have found more support for the controversial assertion that a toxic microbe called Pfiesteria is responsible for massive fish die-offs along the eastern United States. But the new studies, which include the first rough sketch of the toxin, have failed to convince skeptics. For 10 years, aquatic ecologist JoAnn Burkholder of North Carolina State University in Raleigh has argued that a potent neurotoxin from the dinoflagellate Pfiesteria has killed more than a billion fish in East Coast estuaries and sickened lab workers and fishers. However, the toxin has not been identified. This past summer, doubts escalated when researchers at the Virginia Institute of Marine Science (VIMS) in Gloucester Point and other universities reported in two top journals that they could not find a toxin, and that Pfiesteria can kill larval fish by feeding on them ( Science , 11 October, p. [346][1]). ![Figure][2] Toxic or just hungry? Scientists disagree on how deadly a sugarlike molecule reportedly made by the Pfiesteria microbe (above) is to fish. CREDIT: VIRGINIA INSTITUTE OF MARINE SCIENCE Last week, at the 10th International Conference on Harmful Algae in St. Petersburg, Florida, Burkholder said that her critics had not established the right conditions for making Pfiesteria produce toxin. Her lab coaxed the strain of Pfiesteria shumwayae used in the VIMS experiments to kill juvenile tilapia in less than 4 hours, which meets her criteria for toxicity. Collaborating chemist Peter Mueller of the National Oceanic and Atmospheric Administration in Charleston, South Carolina, described a toxic chemical isolated from Burkholder's fish-killing Pfiesteria strains. Burkholder says the NOAA lab also detected this chemical in water and cells from the VIMS strain. It appears to be a glycoside, a molecule that's half sugar, half some other chemical group that hasn't been identified. Other algal toxin researchers remain skeptical. Wayne Carmichael of Wright State University in Dayton, Ohio, says that, although he knows of one other algal toxin that's a glycoside, this kind is unlikely to cause the neurotoxic effects reported in fish and humans. “It would not explain the range” of observations, he says. VIMS fish pathologist Wolfgang Vogelbein points out that nobody has yet shown that this purified toxin produces the lesions he sees on fish physically attacked by Pfiesteria. Burkholder's critics want the chance to test her toxic strains. Burkholder, who has long been criticized for not sharing her strains, says that “there were discussions” at the meeting of organizing blind testing of her cultures by other labs, but it's “still in the planning stages.” The key issue, she says, is for other scientists to follow her protocols. [1]: /lookup/doi/10.1126/science.298.5592.346 [2]: pending:yes

LIFE CYCLE OF THE HETEROTROPHIC DINOFLAGELLATE PFIESTERIA PISCICIDA (DINOPHYCEAE)1

The putatively toxic dinoflagellate Pfiesteria piscicida (Steidinger et Burkholder) has been reported to have an unusual life cycle for a free-living marine dinoflagellate. As many as 24 life cycle stages were originally described for this species. During a recent phylogenetic study in which we used clonal cultures of P. piscicida, we were unable to confirm many reported life cycle stages. To resolve this discrepancy, we undertook a rigorous examination of the life cycle of P. piscicida using nuclear staining techniques combined with traditional light microscopy, high-resolution video microscopy, EM, and in situ hybridization with a suite of fluorescently labeled peptide nucleic acid (PNA) probes. The results showed that P. piscicida had a typical haplontic dinoflagellate life cycle. Asexual division occurred within a division cyst and not by binary fission of motile cells. Sexual reproduction of this homothallic species occurred via the fusion of isogamous gametes. Examination of tanks where P. piscicida was actively feeding on fish showed that amoebae were present; however, they were contaminants introduced with the fish. Whole cell probing using in situ hybridization techniques confirmed that these amoebae were hybridization negative for a P. piscicida-specific PNA probe. Direct observations of clonal P. piscicida cultures revealed no unusual life cycle stages. Furthermore, the results of this study provided no evidence for transformations to amoebae. We therefore conclude that P. piscicida has a life cycle typical of free-living marine dinoflagellates and lacks any amoeboid or other specious stages.

Interactions between the toxic estuarine dinoflagellate Pfiesteria piscicida and two species of bivalve molluscs

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 245:1-10 (2002) - doi:10.3354/meps245001 Interactions between the toxic estuarine dinoflagellate Pfiesteria piscicida and two species of bivalve molluscs Jeffrey J. Springer1,*, Sandra E. Shumway2, JoAnn M. Burkholder1, Howard B. Glasgow1 1Center for Applied Aquatic Ecology, North Carolina State University, 620 Hutton Street, Suite 104, Raleigh, North Carolina 27606, USA 2Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, Connecticut 06340, USA *Email: jeff_springer@ncsu.edu ABSTRACT: Toxic strains of Pfiesteria spp. produce toxin(s) that can cause finfish death, but much less is known about impacts of Pfiesteria on shellfish. Here we conducted 4 experiments to examine interactions between shellfish and toxic (actively toxic or TOX-A from finfish-killing cultures and potentially toxic or TOX-B from cultures without finfish) and non-inducible (NON-IND, apparently incapable of killing fish via a toxic effect) strains of P. piscicida. First (Expt 1), we documented direct physical attack by P. piscicida TOX-A, TOX-B, and NON-IND zoospores on larvae of the bay scallop Argopecten irradians (Lamarck, 1819) and the eastern oyster Crassostrea virginica (Gmelin, 1791). Within 5 min zoospores swarmed around larvae that had discarded their vela, and attached with their peduncles. Within 15 min they had penetrated into the shellfish visceral cavity and had begun to feed aggressively; after 30 min all shellfish tissues except the adductor muscle had been consumed. Second, we tested the response of scallop larvae to P. piscicida (TOX-A or TOX-B) or cryptomonads (as controls) that were held in dialysis tubing (0.22 µm porosity) to prevent direct contact. After 60 min larval survival was 0% in the TOX-A treatment, 100% in the cryptomonad control, and intermediate in TOX-B and TOX-B + cryptomonad treatments. The data indicate a toxic effect of P. piscicida zoospores on the larvae, separate from the physical effect shown in Expt 1. Third, we compared grazing by juvenile and adult oysters on TOX-A, TOX-B, and NON-IND P. piscicida zoospores from the medium. After 60 min, grazing by juvenile oysters significantly differed as NON-IND >> TOX-B >> TOX-A. In contrast, adult oysters grazed significantly fewer TOX-A zoospores and maintained comparable grazing on TOX-B and NON-IND zoospores. Thus juvenile oysters, but not adults, were sensitive to residual toxicity of TOX-B zoospores, and both life-history stages were sensitive to TOX-A zoospores. The adverse effects of toxic strains on larval survival and juvenile grazing indicate that P. piscicida could potentially affect shellfish recruitment. Fourth, we assessed zoospore survival after passage through the digestive tract of adult oysters. The feces contained many temporary cysts from zoospores, and within 24 h >75% of the cysts produced motile cells. The data indicate that adult oysters would be poor biocontrol agents of P. piscicida, given the high survival of ingested zoospores following gut passage and fecal elimination; and that oysters could act as vectors of toxic P. piscicida strains if transported from affected estuaries to other waters. KEY WORDS: Argopecten irradians · Crassostrea virginica · Oyster · Pfiesteria · Scallop · Shellfish · Temporary cyst · Toxic dinoflagellate Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 245. Online publication date: December 18, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.