A review of: Burkholder et al (1992). New 'phantom' dinoflagellate is the causative agent of major estuarine fish kills. Nature 358, 407-410.
The work I am reviewing was first published in 1992, however there have been many papers written in response to this one up to the present day causing huge debate on the topic. This review tries to summarise the work of Burkholder and also the published responses to it. As you will see, it is quite a progressive topic and it definitely doesn’t have a simple end.
The study starts in 1988, where Tilapia (a freshwater cichlid) kept in an aquaria containing water from an estuary in North Carolina, were found to die. It was identified that the cause was a new dinoflagellate, Pfiesteria piscicida. The organism is known as the “phantom dinoflagellate” or the “ambush predator” due to studies of its behaviour; it is seen to lie dormant after causing the mortality of fish, only to reappear when new live fish are input. The estuary itself was then also found to contain links between the dinoflagellate and a great number of fish deaths. Burkholder has studied this dinoflagellate from the beginning, identifying unusual behaviour and an equally unusual life cycle, including at least 24 flagellated, amoeboid and encysted stages. This research on the organism’s life cycle has also been confirmed by researchers since, but has also raised debate and disagreement.
The species was also initially linked to serious health problems in people who came into contact with it, causing skin, respiratory and even mental defects. This is where it has earned its name – the cell from hell. However this is still much in debate since a study sponsored by the Centres for Disease Control showed no relationship between the dinoflagellate and these effects. But further studies are continuing to address the possible connection with Pfiesteria and its close relatives. It was also put into place that the dinoflagellate could only be studied using Biosafety level 3 (BSL-3) precautions which are also used for HIV.
Many researchers have set out to prove that Burkholder’s work in this area is incorrect...
Some fish biologists have suggested that other factors such as low oxygen could explain many fish kills and deep sores typically found on affected fish could have other causes too, such as a fungus.
The 24 stage life cycle which Burkholder describes has also been challenged by research such as that by Kaiser (2002) which has claimed to show a much simpler and more typical life cycle.
Another team attempted to follow Burkholder’s procedure and reported that Pfiesteria attack and kill fish without making a toxin. The same team tried to prove further that direct contact between the dinoflagellate and fish were needed by separating the Pfiesteria cells with a membrane, reporting that fish then did not die.
A paper published online for the Proceedings of the National Academy of Sciences suggested that Pfiesteria lacks the genes to make polyketide toxins (typically produced by fish-killing dinoflagellates). This paper explains that fish kills must have been caused by other factors such as a different toxic alga.
Other factors have also been suggested by more researchers who identified that there are more than 60 organisms living in fish tanks which could also possibly have produced a toxin.
Burkholder has been widely criticised for her work but also has a credible amount of support. She has challenged all criticism of her work and has often produced results to disprove the theories of her rivals. For example, she separated the fish from toxic cells by a membrane like another study had where researchers has tried to replicate her procedures, only to find complete opposite results. She found that in these conditions fish still died, proving that the conditions used in other researchers experiments must not have been the same. She believes that other researchers have ignored her protocols and therefore failed to culture toxic Pfiesteria for their experiments. This has lead to the performance of unsuccessful replication studies where the same results simply cannot be obtained.
The progression of knowledge of this organism and its toxin production is extremely slow and still holds a lot of mystery. Research has been slowed by the potential health risk, even though work has been performed showing no link to neurological changes. Burkholder is reluctant to provide other researchers with her cultures, due to cost but also lack of understanding and willingness to use what she feels is correct protocol. Although Burkholder herself may be slowing the research of the toxin, she raises an important point in saying that identifying algal toxins can be incredibly difficult and scientists shouldn’t expect such quick and obvious results. It took 25 years before the correct identification of the Brevetoxin, a neurotoxin produced by another dinoflagellate – Karenia brevis. However, it has now been more than 20 years since research began on Pfiesteria piscicida and it is still quite the mystery.
This review summarises a variety of research, not just from this 1992 paper, but from many papers since this date published by Burkholder and other researchers. If you would like to read any of these they can be found following a simple search for Burkholder or Pfiesteria piscicida. Popular researchers have been Kaiser, Litaker, Steidinger, Glasgow, Vogelbein and Bowers, to name a few.
The study starts in 1988, where Tilapia (a freshwater cichlid) kept in an aquaria containing water from an estuary in North Carolina, were found to die. It was identified that the cause was a new dinoflagellate, Pfiesteria piscicida. The organism is known as the “phantom dinoflagellate” or the “ambush predator” due to studies of its behaviour; it is seen to lie dormant after causing the mortality of fish, only to reappear when new live fish are input. The estuary itself was then also found to contain links between the dinoflagellate and a great number of fish deaths. Burkholder has studied this dinoflagellate from the beginning, identifying unusual behaviour and an equally unusual life cycle, including at least 24 flagellated, amoeboid and encysted stages. This research on the organism’s life cycle has also been confirmed by researchers since, but has also raised debate and disagreement.
The species was also initially linked to serious health problems in people who came into contact with it, causing skin, respiratory and even mental defects. This is where it has earned its name – the cell from hell. However this is still much in debate since a study sponsored by the Centres for Disease Control showed no relationship between the dinoflagellate and these effects. But further studies are continuing to address the possible connection with Pfiesteria and its close relatives. It was also put into place that the dinoflagellate could only be studied using Biosafety level 3 (BSL-3) precautions which are also used for HIV.
Many researchers have set out to prove that Burkholder’s work in this area is incorrect...
Some fish biologists have suggested that other factors such as low oxygen could explain many fish kills and deep sores typically found on affected fish could have other causes too, such as a fungus.
The 24 stage life cycle which Burkholder describes has also been challenged by research such as that by Kaiser (2002) which has claimed to show a much simpler and more typical life cycle.
Another team attempted to follow Burkholder’s procedure and reported that Pfiesteria attack and kill fish without making a toxin. The same team tried to prove further that direct contact between the dinoflagellate and fish were needed by separating the Pfiesteria cells with a membrane, reporting that fish then did not die.
A paper published online for the Proceedings of the National Academy of Sciences suggested that Pfiesteria lacks the genes to make polyketide toxins (typically produced by fish-killing dinoflagellates). This paper explains that fish kills must have been caused by other factors such as a different toxic alga.
Other factors have also been suggested by more researchers who identified that there are more than 60 organisms living in fish tanks which could also possibly have produced a toxin.
Burkholder has been widely criticised for her work but also has a credible amount of support. She has challenged all criticism of her work and has often produced results to disprove the theories of her rivals. For example, she separated the fish from toxic cells by a membrane like another study had where researchers has tried to replicate her procedures, only to find complete opposite results. She found that in these conditions fish still died, proving that the conditions used in other researchers experiments must not have been the same. She believes that other researchers have ignored her protocols and therefore failed to culture toxic Pfiesteria for their experiments. This has lead to the performance of unsuccessful replication studies where the same results simply cannot be obtained.
The progression of knowledge of this organism and its toxin production is extremely slow and still holds a lot of mystery. Research has been slowed by the potential health risk, even though work has been performed showing no link to neurological changes. Burkholder is reluctant to provide other researchers with her cultures, due to cost but also lack of understanding and willingness to use what she feels is correct protocol. Although Burkholder herself may be slowing the research of the toxin, she raises an important point in saying that identifying algal toxins can be incredibly difficult and scientists shouldn’t expect such quick and obvious results. It took 25 years before the correct identification of the Brevetoxin, a neurotoxin produced by another dinoflagellate – Karenia brevis. However, it has now been more than 20 years since research began on Pfiesteria piscicida and it is still quite the mystery.
This review summarises a variety of research, not just from this 1992 paper, but from many papers since this date published by Burkholder and other researchers. If you would like to read any of these they can be found following a simple search for Burkholder or Pfiesteria piscicida. Popular researchers have been Kaiser, Litaker, Steidinger, Glasgow, Vogelbein and Bowers, to name a few.
2 comments:
Wow sounds like quite a heated ongoing debate. Who are you backing?
If all of Burkholder's research is correct it sounds like this dinoflagellate could become rather infamous through more research.
You mentioned that Burkholder said "identifying algal toxins can be incredibly difficult" Do you know what makes it so difficult to indentify toxins like the Brevetoxin? Found in very low concentrations prehaps? Or possibly hard to isolate among many other marine chemicals?
It is hard to imagine the excitement and controversy that this aroused in the 1990s, especially in the US. It had huge political implications, now it is largely forgotten. There's a great popular book 'And the Rivers turned to Blood' by Rodney Barker. I always thought it would make a great movie, with Julia Roberts in the lead role. now, it is largely forgotten now and it's hard to find objective recent reviews about it.As far as the human health aspects go, it definitely does look like a case of Pfiesteria hysteria. There's a bit more about the story in Chapter 12 of the book, but when updating it, I found it hard to get clear views. everyone seems to want to forget about the episode, very strange.
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