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Pfiesteria shumwayae kills fish by micropredation not exotoxin secretion

Abstract

Pfiesteria piscicida and P. shumwayae reportedly secrete potent exotoxins thought to cause fish lesion events, acute fish kills and human disease in mid-Atlantic USA estuaries1,2,3,4,5,6,7. However, Pfiesteria toxins have never been isolated or characterized8. We investigated mechanisms by which P. shumwayae kills fish using three different approaches. Here we show that larval fish bioassays conducted in tissue culture plates fitted with polycarbonate membrane inserts exhibited mortality (100%) only in treatments where fish and dinospores were in physical contact. No mortalities occurred in treatments where the membrane prevented contact between dinospores and fish. Using differential centrifugation and filtration of water from a fish-killing culture, we produced ‘dinoflagellate’, ‘bacteria’ and ‘cell-free’ fractions. Larval fish bioassays of these fractions resulted in mortalities (60–100% in less than 24 h) only in fractions containing live dinospores (‘whole water’, ‘dinoflagellate’), with no mortalities in ‘cell-free’ or ‘bacteria’-enriched fractions. Videomicrography and electron microscopy show dinospores swarming toward and attaching to skin, actively feeding, and rapidly denuding fish of epidermis. We show here that our cultures of actively fish-killing P. shumwayae do not secrete potent exotoxins; rather, fish mortality results from micropredatory feeding.

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Figure 1
Figure 2: Results from bioassays using larval Cyprinodon variegatus exposed in six-well tissue culture plates fitted with polycarbonate membrane inserts.
Figure 3: Fractionation assay with larval Fundulus heteroclitus using a Pfiesteria shumwayae culture that actively killed tilapia in a 38-l assay.
Figure 4: Myzocytosis by Pfiesteria shumwayae on the epidermis of larval Cyprinodon variegatus.

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Acknowledgements

C. Squyars, A. Miller, P. Blake, D. Zwerner, E. Westcott, V. Foster, L. Ott, E. Walker, J. Watts, W. Ribeiro and K. Hudson contributed significantly to this investigation. E. M. Burreson provided support and critical review. This work was funded in part by ECOHAB (Ecology and Oceanography of Harmful Algal Blooms) grants from the EPA, the EPA with the National Oceanic and Atmospheric Administration (NOAA), and from the NOAA; the Commonwealth of Virginia's Pfiesteria Initiative; and the Centers for Disease Control and Prevention. We thank T. Shedd and the US Army Center for Environmental Health Research for the lease of the BSL3 laboratory.

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Correspondence to Wolfgang K. Vogelbein.

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Vogelbein, W., Lovko, V., Shields, J. et al. Pfiesteria shumwayae kills fish by micropredation not exotoxin secretion. Nature 418, 967–970 (2002). https://doi.org/10.1038/nature01008

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