Literature Review of the Microalga Prymnesium parvum and its Associated Toxicity
Sean Watson, Texas Parks and Wildlife Department, August 2001
Conclusion and Areas of Further Research
The biological and ecological significance of the synthesis and release of the Prymnesium parvum toxin is not clear. However, it is now known that this microalga produces two glycosidic toxins, prymnesin-1 and prymnesin-2, collectively called prymnesin, and that the two similar toxins have both hemolytic and ichthyotoxic activity (Igarashi et al. 1999). Does prymnesin have negative effects on the competitors of P. parvum that would lend an advantage to the growth and success of this flagellate? It has been proposed that a critical concentration of a “growth-initiating factor” is required to start division in this species and yield blooms, but this factor (if it exists) has not been described and is an area of additional research (Glass et al. 1991). If a “growth-initiating factor” is discovered, it could lead to an effective means of controlling P. parvum. The targeting of alkaline phosphates for the control of this microalga is another area that will require additional research if it is indeed possible. The synthesis of DMSP and the unknown polyol believed to aid in the osmoregulation of P. parvum needs to be studied further. This, too, may lead to an effective control of this microalga.
Additional research is needed to determine which types of bacteria cause a decrease in P. parvum toxicity (Nygaard and Tobiesen 1993). These bacteria could be potential biological control agents, and prove to be more practical in the control of P. parvum blooms that cover large areas in sensitive aquatic environments.
It seems that the most important factor governing the toxicity of P. parvum blooms is the relative amounts of nitrogen and phosphorous found in the water, and that limitation of both of these nutrients seems to cause an increase in toxicity (Johansson and Graneli 1999). Additional research must be conducted in this area to determine if an unbalanced N:P ratio indeed leads to increased toxicity. If the N:P ratio proves to be the most important factor, research must be conducted to determine how the optimum N:P ratio for P. parvum can be restored. The sources for the imbalance must also be studied since it seems that nitrogen and phosphorous inputs from agriculture, aquaculture and other sources may be involved. P. parvum has been found to graze bacteria as a source of phosphate (Nygaard and Tobiesen 1993). More research in this area may lead to ways of treating P. parvum blooms in phosphate-limited environments by supplying this microalga with bacteria it is known to utilize as a source of phosphate.
Glycerol has been found to enhance the growth of P. parvum (Cheng and Antia1970). Are there any sources of glycerol pollution in the areas where fish kills occurred in Texas? The investigation of future fish kills should include the detection of glycerol in the aquatic environment since this may cause P. parvum blooms.
The importance of the microscopic algae Prymnesium parvum can be seen in the millions of fish killed across the globe, and the ensuing economic losses it creates. The recent appearance of P. parvum in Texas, and the recurring fish kills caused by the toxins released, is a cause for concern. This problem is one that must be addressed soon for history has shown us that P. parvum is ever present once the organism first appears. Steps must be taken to further understand the ecology of this organism, its toxin and causes of toxic blooms in an attempt to decrease the number of occurrences we see in the future.
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